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- Forouzanfar, Mohammad H, et al.
(författare)
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Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks in 188 countries, 1990-2013 : a systematic analysis for the Global Burden of Disease Study 2013.
- 2015
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 386:10010, s. 2287-2323
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The Global Burden of Disease, Injuries, and Risk Factor study 2013 (GBD 2013) is the first of a series of annual updates of the GBD. Risk factor quantification, particularly of modifiable risk factors, can help to identify emerging threats to population health and opportunities for prevention. The GBD 2013 provides a timely opportunity to update the comparative risk assessment with new data for exposure, relative risks, and evidence on the appropriate counterfactual risk distribution.METHODS: Attributable deaths, years of life lost, years lived with disability, and disability-adjusted life-years (DALYs) have been estimated for 79 risks or clusters of risks using the GBD 2010 methods. Risk-outcome pairs meeting explicit evidence criteria were assessed for 188 countries for the period 1990-2013 by age and sex using three inputs: risk exposure, relative risks, and the theoretical minimum risk exposure level (TMREL). Risks are organised into a hierarchy with blocks of behavioural, environmental and occupational, and metabolic risks at the first level of the hierarchy. The next level in the hierarchy includes nine clusters of related risks and two individual risks, with more detail provided at levels 3 and 4 of the hierarchy. Compared with GBD 2010, six new risk factors have been added: handwashing practices, occupational exposure to trichloroethylene, childhood wasting, childhood stunting, unsafe sex, and low glomerular filtration rate. For most risks, data for exposure were synthesised with a Bayesian meta-regression method, DisMod-MR 2.0, or spatial-temporal Gaussian process regression. Relative risks were based on meta-regressions of published cohort and intervention studies. Attributable burden for clusters of risks and all risks combined took into account evidence on the mediation of some risks such as high body-mass index (BMI) through other risks such as high systolic blood pressure and high cholesterol.FINDINGS: All risks combined account for 57·2% (95% uncertainty interval [UI] 55·8-58·5) of deaths and 41·6% (40·1-43·0) of DALYs. Risks quantified account for 87·9% (86·5-89·3) of cardiovascular disease DALYs, ranging to a low of 0% for neonatal disorders and neglected tropical diseases and malaria. In terms of global DALYs in 2013, six risks or clusters of risks each caused more than 5% of DALYs: dietary risks accounting for 11·3 million deaths and 241·4 million DALYs, high systolic blood pressure for 10·4 million deaths and 208·1 million DALYs, child and maternal malnutrition for 1·7 million deaths and 176·9 million DALYs, tobacco smoke for 6·1 million deaths and 143·5 million DALYs, air pollution for 5·5 million deaths and 141·5 million DALYs, and high BMI for 4·4 million deaths and 134·0 million DALYs. Risk factor patterns vary across regions and countries and with time. In sub-Saharan Africa, the leading risk factors are child and maternal malnutrition, unsafe sex, and unsafe water, sanitation, and handwashing. In women, in nearly all countries in the Americas, north Africa, and the Middle East, and in many other high-income countries, high BMI is the leading risk factor, with high systolic blood pressure as the leading risk in most of Central and Eastern Europe and south and east Asia. For men, high systolic blood pressure or tobacco use are the leading risks in nearly all high-income countries, in north Africa and the Middle East, Europe, and Asia. For men and women, unsafe sex is the leading risk in a corridor from Kenya to South Africa.INTERPRETATION: Behavioural, environmental and occupational, and metabolic risks can explain half of global mortality and more than one-third of global DALYs providing many opportunities for prevention. Of the larger risks, the attributable burden of high BMI has increased in the past 23 years. In view of the prominence of behavioural risk factors, behavioural and social science research on interventions for these risks should be strengthened. Many prevention and primary care policy options are available now to act on key risks.FUNDING: Bill & Melinda Gates Foundation.
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2. |
- Vos, Theo, et al.
(författare)
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Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013
- 2015
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Ingår i: The Lancet. - 1474-547X .- 0140-6736. ; 386:9995, s. 743-800
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Tidskriftsartikel (refereegranskat)abstract
- Background Up-to-date evidence about levels and trends in disease and injury incidence, prevalence, and years lived with disability (YLDs) is an essential input into global, regional, and national health policies. In the Global Burden of Disease Study 2013 (GBD 2013), we estimated these quantities for acute and chronic diseases and injuries for 188 countries between 1990 and 2013. Methods Estimates were calculated for disease and injury incidence, prevalence, and YLDs using GBD 2010 methods with some important refinements. Results for incidence of acute disorders and prevalence of chronic disorders are new additions to the analysis. Key improvements include expansion to the cause and sequelae list, updated systematic reviews, use of detailed injury codes, improvements to the Bayesian meta-regression method (DisMod-MR), and use of severity splits for various causes. An index of data representativeness, showing data availability, was calculated for each cause and impairment during three periods globally and at the country level for 2013. In total, 35 620 distinct sources of data were used and documented to calculated estimates for 301 diseases and injuries and 2337 sequelae. The comorbidity simulation provides estimates for the number of sequelae, concurrently, by individuals by country, year, age, and sex. Disability weights were updated with the addition of new population-based survey data from four countries. Findings Disease and injury were highly prevalent; only a small fraction of individuals had no sequelae. Comorbidity rose substantially with age and in absolute terms from 1990 to 2013. Incidence of acute sequelae were predominantly infectious diseases and short-term injuries, with over 2 billion cases of upper respiratory infections and diarrhoeal disease episodes in 2013, with the notable exception of tooth pain due to permanent caries with more than 200 million incident cases in 2013. Conversely, leading chronic sequelae were largely attributable to non-communicable diseases, with prevalence estimates for asymptomatic permanent caries and tension-type headache of 2.4 billion and 1.6 billion, respectively. The distribution of the number of sequelae in populations varied widely across regions, with an expected relation between age and disease prevalence. YLDs for both sexes increased from 537.6 million in 1990 to 764.8 million in 2013 due to population growth and ageing, whereas the age-standardised rate decreased little from 114.87 per 1000 people to 110.31 per 1000 people between 1990 and 2013. Leading causes of YLDs included low back pain and major depressive disorder among the top ten causes of YLDs in every country. YLD rates per person, by major cause groups, indicated the main drivers of increases were due to musculoskeletal, mental, and substance use disorders, neurological disorders, and chronic respiratory diseases; however HIV/AIDS was a notable driver of increasing YLDs in sub-Saharan Africa. Also, the proportion of disability-adjusted life years due to YLDs increased globally from 21.1% in 1990 to 31.2% in 2013. Interpretation Ageing of the world's population is leading to a substantial increase in the numbers of individuals with sequelae of diseases and injuries. Rates of YLDs are declining much more slowly than mortality rates. The non-fatal dimensions of disease and injury will require more and more attention from health systems. The transition to non-fatal outcomes as the dominant source of burden of disease is occurring rapidly outside of sub-Saharan Africa. Our results can guide future health initiatives through examination of epidemiological trends and a better understanding of variation across countries.
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3. |
- Naghavi, Mohsen, et al.
(författare)
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Global, regional, and national age-sex specific all-cause and cause-specific mortality for 240 causes of death, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013
- 2015
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Ingår i: The Lancet. - 1474-547X .- 0140-6736. ; 385:9963, s. 117-171
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Tidskriftsartikel (refereegranskat)abstract
- Background Up-to-date evidence on levels and trends for age-sex-specifi c all-cause and cause-specifi c mortality is essential for the formation of global, regional, and national health policies. In the Global Burden of Disease Study 2013 (GBD 2013) we estimated yearly deaths for 188 countries between 1990, and 2013. We used the results to assess whether there is epidemiological convergence across countries. Methods We estimated age-sex-specifi c all-cause mortality using the GBD 2010 methods with some refinements to improve accuracy applied to an updated database of vital registration, survey, and census data. We generally estimated cause of death as in the GBD 2010. Key improvements included the addition of more recent vital registration data for 72 countries, an updated verbal autopsy literature review, two new and detailed data systems for China, and more detail for Mexico, UK, Turkey, and Russia. We improved statistical models for garbage code redistribution. We used six different modelling strategies across the 240 causes; cause of death ensemble modelling (CODEm) was the dominant strategy for causes with sufficient information. Trends for Alzheimer's disease and other dementias were informed by meta-regression of prevalence studies. For pathogen-specifi c causes of diarrhoea and lower respiratory infections we used a counterfactual approach. We computed two measures of convergence (inequality) across countries: the average relative difference across all pairs of countries (Gini coefficient) and the average absolute difference across countries. To summarise broad findings, we used multiple decrement life-tables to decompose probabilities of death from birth to exact age 15 years, from exact age 15 years to exact age 50 years, and from exact age 50 years to exact age 75 years, and life expectancy at birth into major causes. For all quantities reported, we computed 95% uncertainty intervals (UIs). We constrained cause-specific fractions within each age-sex-country-year group to sum to all-cause mortality based on draws from the uncertainty distributions. Findings Global life expectancy for both sexes increased from 65.3 years (UI 65.0-65.6) in 1990, to 71.5 years (UI 71.0-71.9) in 2013, while the number of deaths increased from 47.5 million (UI 46.8-48.2) to 54.9 million (UI 53.6-56.3) over the same interval. Global progress masked variation by age and sex: for children, average absolute diff erences between countries decreased but relative diff erences increased. For women aged 25-39 years and older than 75 years and for men aged 20-49 years and 65 years and older, both absolute and relative diff erences increased. Decomposition of global and regional life expectancy showed the prominent role of reductions in age-standardised death rates for cardiovascular diseases and cancers in high-income regions, and reductions in child deaths from diarrhoea, lower respiratory infections, and neonatal causes in low-income regions. HIV/AIDS reduced life expectancy in southern sub-Saharan Africa. For most communicable causes of death both numbers of deaths and age-standardised death rates fell whereas for most non-communicable causes, demographic shifts have increased numbers of deaths but decreased age-standardised death rates. Global deaths from injury increased by 10.7%, from 4.3 million deaths in 1990 to 4.8 million in 2013; but age-standardised rates declined over the same period by 21%. For some causes of more than 100 000 deaths per year in 2013, age-standardised death rates increased between 1990 and 2013, including HIV/AIDS, pancreatic cancer, atrial fibrillation and flutter, drug use disorders, diabetes, chronic kidney disease, and sickle-cell anaemias. Diarrhoeal diseases, lower respiratory infections, neonatal causes, and malaria are still in the top five causes of death in children younger than 5 years. The most important pathogens are rotavirus for diarrhoea and pneumococcus for lower respiratory infections. Country-specific probabilities of death over three phases of life were substantially varied between and within regions. Interpretation For most countries, the general pattern of reductions in age-sex specifi c mortality has been associated with a progressive shift towards a larger share of the remaining deaths caused by non-communicable disease and injuries. Assessing epidemiological convergence across countries depends on whether an absolute or relative measure of inequality is used. Nevertheless, age-standardised death rates for seven substantial causes are increasing, suggesting the potential for reversals in some countries. Important gaps exist in the empirical data for cause of death estimates for some countries; for example, no national data for India are available for the past decade.
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7. |
- Wang, Haidong, et al.
(författare)
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Estimates of global, regional, and national incidence, prevalence, and mortality of HIV, 1980-2015 : the Global Burden of Disease Study 2015.
- 2016
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Ingår i: The lancet. HIV. - : Elsevier. - 2352-3018. ; 3:8, s. e361-e387
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Timely assessment of the burden of HIV/AIDS is essential for policy setting and programme evaluation. In this report from the Global Burden of Disease Study 2015 (GBD 2015), we provide national estimates of levels and trends of HIV/AIDS incidence, prevalence, coverage of antiretroviral therapy (ART), and mortality for 195 countries and territories from 1980 to 2015.METHODS: For countries without high-quality vital registration data, we estimated prevalence and incidence with data from antenatal care clinics and population-based seroprevalence surveys, and with assumptions by age and sex on initial CD4 distribution at infection, CD4 progression rates (probability of progression from higher to lower CD4 cell-count category), on and off antiretroviral therapy (ART) mortality, and mortality from all other causes. Our estimation strategy links the GBD 2015 assessment of all-cause mortality and estimation of incidence and prevalence so that for each draw from the uncertainty distribution all assumptions used in each step are internally consistent. We estimated incidence, prevalence, and death with GBD versions of the Estimation and Projection Package (EPP) and Spectrum software originally developed by the Joint United Nations Programme on HIV/AIDS (UNAIDS). We used an open-source version of EPP and recoded Spectrum for speed, and used updated assumptions from systematic reviews of the literature and GBD demographic data. For countries with high-quality vital registration data, we developed the cohort incidence bias adjustment model to estimate HIV incidence and prevalence largely from the number of deaths caused by HIV recorded in cause-of-death statistics. We corrected these statistics for garbage coding and HIV misclassification.FINDINGS: Global HIV incidence reached its peak in 1997, at 3·3 million new infections (95% uncertainty interval [UI] 3·1-3·4 million). Annual incidence has stayed relatively constant at about 2·6 million per year (range 2·5-2·8 million) since 2005, after a period of fast decline between 1997 and 2005. The number of people living with HIV/AIDS has been steadily increasing and reached 38·8 million (95% UI 37·6-40·4 million) in 2015. At the same time, HIV/AIDS mortality has been declining at a steady pace, from a peak of 1·8 million deaths (95% UI 1·7-1·9 million) in 2005, to 1·2 million deaths (1·1-1·3 million) in 2015. We recorded substantial heterogeneity in the levels and trends of HIV/AIDS across countries. Although many countries have experienced decreases in HIV/AIDS mortality and in annual new infections, other countries have had slowdowns or increases in rates of change in annual new infections.INTERPRETATION: Scale-up of ART and prevention of mother-to-child transmission has been one of the great successes of global health in the past two decades. However, in the past decade, progress in reducing new infections has been slow, development assistance for health devoted to HIV has stagnated, and resources for health in low-income countries have grown slowly. Achievement of the new ambitious goals for HIV enshrined in Sustainable Development Goal 3 and the 90-90-90 UNAIDS targets will be challenging, and will need continued efforts from governments and international agencies in the next 15 years to end AIDS by 2030.
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8. |
- Catapano, Filomena, et al.
(författare)
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In Situ Evidence of Ion Acceleration between Consecutive Reconnection Jet Fronts
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 908:1
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Tidskriftsartikel (refereegranskat)abstract
- Processes driven by unsteady reconnection can efficiently accelerate particles in many astrophysical plasmas. An example is the reconnection jet fronts in an outflow region. We present evidence of suprathermal ion acceleration between two consecutive reconnection jet fronts observed by the Magnetospheric Multiscale mission in the terrestrial magnetotail. An earthward propagating jet is approached by a second faster jet. Between the jets, the thermal ions are mostly perpendicular to magnetic field, are trapped, and are gradually accelerated in the parallel direction up to 150 keV. Observations suggest that ions are predominantly accelerated by a Fermi-like mechanism in the contracting magnetic bottle formed between the two jet fronts. The ion acceleration mechanism is presumably efficient in other environments where jet fronts produced by variable rates of reconnection are common and where the interaction of multiple jet fronts can also develop a turbulent environment, e.g., in stellar and solar eruptions.
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9. |
- Lee, Justin H., et al.
(författare)
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MMS Measurements and Modeling of Peculiar Electromagnetic Ion Cyclotron Waves
- 2019
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007.
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Tidskriftsartikel (refereegranskat)abstract
- Orbiting Earth's dayside outer magnetosphere on 29 September 2015, the Magnetospheric Multiscale (MMS) satellites measured plasma composition, simultaneous electromagnetic ion cyclotron waves, and intermittent fast plasma flows consistent with ultralow frequency waves or convection. Such flows can accelerate typically unobservable low-energy plasma into a measurable energy range of spacecraft plasma instrumentation. We exploit the flow occurrence to ensure measurement of cold ion species alongside the hot particles-consisting of ionospheric heavy ions and solar wind He++-during a subinterval of wave emissions with spectral properties previously described as peculiar. Through application of the composition and multisatellite wave vector data to linear theory, we demonstrate the emissions are in fact consistent with theory, growing naturally in the He++ band with sufficient free energy.
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10. |
- Nakamura, Rumi, et al.
(författare)
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Multiscale Currents Observed by MMS in the Flow Braking Region
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:2, s. 1260-1278
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Tidskriftsartikel (refereegranskat)abstract
- We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold ExB drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.
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11. |
- Zhang, L. Q., et al.
(författare)
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BBF Deceleration Down-Tail of X <-15 RE From MMS Observation
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 125:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the direct observation on bursty bulk flow (BBF) deceleration down-tail of X < -15 R-E by MMS satellite. Two typical events are presented in the paper. In the first event on 05 June 2018, MMS1 is located at X similar to -16.1 R-E and records four individual bursty flows (BFs). Each burst flow has distinctly lower velocity than the preceding one. Accompanying with the decelerated BFs, the Bz/Bx continuously increases/decreases. Simultaneous Vx-decrease and Bz-increase are in coincidence with the scenario of the local BBF deceleration and formation of the magnetic pileup region. In the second event on 03 July 2017, MMS stays in the neutral sheet of X similar to -24.5 R-E, and encounters similar BBF deceleration process. For both events, the decelerated BF series exhibit prominent medium-energy ion component (2-10 KeV). Analyses show enhanced parallel current (J(//)) and Kinetic Alfvenic wave (KAW) emitting during the BF intervals. The strength of the emitted KAW has a clear tendency to decay with the BBF decreasing. Power spectra density analysis confirms the substantial Joule dissipation during the BBF deceleration, both J(//) and J(perpendicular to). Combined analyses support BBF dissipation via Joule heating as well as KAW emitting. Finally, we propose a possible mechanism on the BBF deceleration, i.e., "collision" with the tailward flow.
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12. |
- Zhang, L. Q., et al.
(författare)
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MMS Observation on the Cross-Tail Current Sheet Roll-up at the Dipolarization Front
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:4
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Tidskriftsartikel (refereegranskat)abstract
- We perform a case study on the evolution of the current sheet in different regions around the dipolarization front (DF), including magnetic-dip preceding the DF, front at the DF, and magnetic pileup region (MPR) behind the DF based on magnetospheric multiscale (MMS) observation on July 31, 2017. In this event, MMS1 stays inside the current sheet during the whole bursty bulk flow (BBF) interval. Our analysis reveals that the cross-tail current sheet at the DF is rolled up, signified by the depression (-V-z/-B-z) at the dip and elevation (+V-z/+B-z) at the front. The minimum variance analysis on the magnetic field method is applied to obtain the normal direction of the current sheet. The result confirms the roll-up, that is, downward at the depressed current sheet and upward at the elevated current sheet. The current sheet roll-up at the DF is asymmetric, with steeper elevation than depression. The elevation angle of the elevated current sheet is evaluated to be similar to 30 degrees. Strong duskward and predominantly perpendicular J spike (similar to 90 nA/m(2)) concentrate at the interface between the dip and the front. The strength of the current of the J-spike is about nine/three times the current at the dip/front. The front is characterized by positive E center dot J. In the dip/MPR, no such preference is seen. Ion/Electron pitch angle distributions exhibit significant and different evolutions in the roll-up current sheet from dip to front, including their energy-dependence and distributions. Finally, the roll-up current sheet could decelerate BBF and change the flow structure. The potential significance of the roll-up current sheet on BBF evolution is emphasized.
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13. |
- Zhang, L. Q., et al.
(författare)
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Turbulent current sheet frozen in bursty bulk flow : observation and model
- 2022
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing four-point joint observations by Magnetospheric Multiscale Spacecraft (MMS), we investigate the main features of the current sheet frozen in (CSFI) the bursty bulk flow. Typical event on the steady long-lasting BBF on July 23, 2017 shows the enhanced dawn-dusk current (Jy(0)) in the CSFI (beta similar to 10). The magnitude of the Jy(0) in the CSFI is about 5.5 nA/m(2). The CSFI is highly turbulent, with the ratio of Delta J/J(0) of similar to 2 (where Delta J is perturbed J). The turbulent CSFI is characterized by intermittent current coherent structures. The magnitude of the spiky-J at coherent structures is typically above 30 nA/m(2). Spectrum analysis exhibits that BBF turbulence follows distinct dissipation laws inside and outside the CSFI. Based on MMS observations, we propose a new model of the BBF in the framework of magnetohydrodynamics. In this model, the BBF is depicted as a closed plasma system with the localized current sheet frozen at the center of the flow (Taylor's hypothesis). In the light of principle of Helmholtz-decomposition, the BBF motion in the tail plasma sheet is explained. The model also predicts the thermal expansion of the BBF after leaving the reconnection source region.
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14. |
- Zhang, L. Q., et al.
(författare)
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Vorticity Within Bursty Bulk Flows : Convective Versus Kinetic
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:3
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Tidskriftsartikel (refereegranskat)abstract
- Based on four-point Magnetospheric Multiscale observation, we carefully analyze the vorticity field in the course of a reconnection jet on 27 June 2017. In this event, the convective electric field (E-c) is overwhelmed by the kinetic electric field (E-k). Accordingly, the omega-field in the course of the BBF is dominated by kinetic vorticity (omega(k)). The omega-field in the E-k-dominated bursty bulk flow (BBF) is characterized by perpendicular anisotropy. Comparison of velocity-curl vorticity (omega= backward difference xV $\mathbf{\omega }=\nabla \times \mathbf{V}$) with E/B induced vorticity confirms a greater contribution to the BBF vorticity by E (omega E=(B. backward difference )E/B2 ${\mathbf{\omega }}_{\mathbf{E}}=(\mathbf{B}\cdot \nabla )\boldsymbol{E}/{\boldsymbol{B}}<^>{2}$) than by B (omega B=(E. backward difference )B/B2 ${\mathbf{\omega }}_{\mathbf{B}}=(\mathbf{E}\cdot \nabla )\mathbf{B}/{\boldsymbol{B}}<^>{2}$). Power spectrum density reveals that in the E-k-dominated BBF, the E-c and E-k spectra have different power laws. E-c dominates the B-spectrum while E-k dominates the E-spectrum. The E-c(B) spectrum has a -5/3-like slope below 0.25 Hz but a -3-like above 0.25 Hz. The E-k(E) spectrum is -5/3-like at the low-frequency end (below 0.1 Hz) but -2-like at the high-frequency end (above 2 Hz). Within its medium frequency range, the spectrum is flat. Particularly, the E-k(E) spectrum exhibits the bump at 1-2 Hz in the frequency domain. The solitary/bipolar E-spikes, with typical temporal scale of 0.3-1 s, are likely responsible for the E-bump. Finally, we statistically analyze and compare the vorticity field in E-k-dominated and E-c -dominated BBFs. The result demonstrates that the E-k-dominated BBF tends to have stronger vorticity than the E-c -dominated BBF.
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15. |
- Carroll, Harriet A., et al.
(författare)
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Effect of acute hypohydration on glycemic regulation in healthy adults : A randomized crossover trial
- 2019
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Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 126:2, s. 422-430
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Tidskriftsartikel (refereegranskat)abstract
- he aim of this study was to investigate the acute effect of hydration status on glycemic regulation in healthy adults and explore underlying mechanisms. In this randomized crossover trial, 16 healthy adults (8 men, 8 women) underwent an oral glucose tolerance test (OGTT) when hypohydrated and rehydrated after 4 days of pretrial standardization. One day before OGTT, participants were dehydrated for 1 h in a heat tent with subsequent fluid restriction (HYPO) or replacement (RE). The following day, an OGTT was performed with metabolic rate measurements and pre- and post-OGTT muscle biopsies. Peripheral quantitative computer tomography thigh scans were taken before and after intervention to infer changes in cell volume. HYPO (but not RE) induced 1.9% (SD 1.2) body mass loss, 2.9% (SD 2.7) cell volume reduction, and increased urinary hydration markers, serum osmolality, and plasma copeptin concentration (all P 0.007). Fasted serum glucose [HYPO 5.10 mmol/l (SD 0.42), RE 5.02 mmol/l (SD 0.40); P 0.327] and insulin [HYPO 27.1 pmol/l (SD 9.7), RE 27.6 pmol/l (SD 9.2); P 0.809] concentrations were similar between HYPO and RE. Hydration status did not alter the serum glucose (P 0.627) or insulin (P 0.200) responses during the OGTT. Muscle water content was lower before OGTT after HYPO compared with RE [761 g/kg wet wt (SD 13) vs. 772 g/kg wet wt (SD 18) RE] but similar after OGTT [HYPO 779 g/kg wet wt (SD 15) vs. RE 780 g/kg wet wt (SD 20); time P 0.011; trial time P 0.055]. Resting energy expenditure was similar between hydration states (stable between 1.21 and 5.94 kJ·kg 1 ·day 1 ; trial P 0.904). Overall, despite acute mild hypohydration increasing plasma copeptin concentrations and decreasing fasted cell volume and muscle water, we found no effect on glycemic regulation.
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16. |
- Carroll, Harriet A., et al.
(författare)
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Hydration status affects thirst and salt preference but not energy intake or postprandial ghrelin in healthy adults : A randomised crossover trial
- 2019
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Ingår i: Physiology and Behavior. - : Elsevier BV. - 0031-9384. ; 212
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Tidskriftsartikel (refereegranskat)abstract
- Background: Few studies have investigated the effect of hydration status on appetite for food in healthy adults. Prior work suggests hydration status does not alter appetite or energy intake, with mixed findings regarding appetite hormone secretion. However, an extensive investigation into both the psychological and physiological appetitive responses to hydration status has never been conducted. Objective: To investigate the effect of hydration status on multiple facets of appetite. Design: After 3 days pre-trial standardization, a range of appetite tasks were conducted when hypohydrated (HYPO) and euhydrated (EUHY) in 16 healthy participants (8 men). Hydration status was manipulated via dehydration in a heat tent for 60 min and subsequent fluid restriction (HYPO) or replacement (EUHY). The next day, a food reward computer task was completed followed by an ad libitum pasta meal. Pre- and post-prandial visual analogue scales assessing hunger, fullness, and flavour desires (sweet, salty, savoury and fatty) were additionally completed. Blood samples were taken the previous day before the hydration interventions in a euhydrated state, and in the fasted and post-prandial state during HYPO and EUHY. Results: HYPO induced -1.9 ± 1.2% body mass change, compared to -0.2 ± 0.6%, with accompanying changes in markers of hypohydration which were not seen during EUHY. A higher desire for foods was associated with a higher water content but the association was weaker in EUHY compared to HYPO, (β= -0.33 mm/g of food water content, p < 0.001) in the food reward task. Visual analogue scales showed similar hunger and fullness between interventions, but during HYPO there was consistently higher thirst (average range in difference 27–32 mm across all time points) and lower fasted desire for salt (−23, 95% CI −10, −35 mm). Ad libitum energy intake (HYPO 1953 ± 742 kJ, EUHY 2027 ± 926 kJ; p = 0.542) and post-prandial ghrelin concentrations (HYPO 180 ± 65 pg mL−1, EUHY 188 ± 71 pg mL−1; p = 0.736) were similar by hydration status. Conclusions: An acute manipulation to hydration status altered desire for salt and foods of differing water contents, but did not influence energy intake at an ad libitum pasta meal. Further research should investigate whether these appetites would alter food choice.
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17. |
- Eriksson, Elin, 1989-, et al.
(författare)
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Electron Energization at a Reconnecting Magnetosheath Current Sheet
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:16, s. 8081-8090
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of electron energization within a sub-ion-scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (similar to 0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations. Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail, the acceleration mechanism and corresponding heating of electrons is similar. Plain Language Summary Magnetic reconnection is an important physical energy conversion process in astrophysical and laboratory plasmas. The easiest place to analyze magnetic reconnection is in near-Earth space. Due to lack of sufficient electron resolution of previous spacecraft missions, there are many unanswered questions regarding electron heating and acceleration processes at small scales. In particular, the regime where thermal pressure dominates over magnetic pressure, the most common state of plasmas in the Universe, is little explored. In this letter we study such a regime using the four-spacecraft Magnetospheric Multiscale mission. We analyze a reconnecting current sheet in the magnetosheath. We show that electrons are energized by a parallel potential, similar to what has been observed in the different plasma regimes the magnetopause and magnetotail. Thus, despite different plasma conditions, a similar acceleration mechanism and corresponding heating of electrons is occurring in all these regions.
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18. |
- Gingell, Imogen, et al.
(författare)
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MMS Observations and Hybrid Simulations of Surface Ripples at a Marginally Quasi-Parallel Shock
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:11, s. 11003-11017
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Tidskriftsartikel (refereegranskat)abstract
- Simulations and observations of collisionless shocks have shown that deviations of the nominal local shock normal orientation, that is, surface waves or ripples, are expected to propagate in the ramp and overshoot of quasi-perpendicular shocks. Here we identify signatures of a surface ripple propagating during a crossing of Earth's marginally quasi-parallel (theta(Bn) similar to 45 degrees) or quasi-parallel bow shock on 27 November 2015 06: 01: 44 UTC by the Magnetospheric Multiscale (MMS) mission and determine the ripple's properties using multispacecraft methods. Using two-dimensional hybrid simulations, we confirm that surface ripples are a feature of marginally quasi-parallel and quasi-parallel shocks under the observed solar wind conditions. In addition, since these marginally quasi-parallel and quasi-parallel shocks are expected to undergo a cyclic reformation of the shock front, we discuss the impact of multiple sources of nonstationarity on shock structure. Importantly, ripples are shown to be transient phenomena, developing faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change in properties of the ripple observed by MMS is consistent with the reformation of the shock front over a time scale of an ion gyroperiod.
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19. |
- Lee, Justin H., et al.
(författare)
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Application of Cold and Hot Plasma Composition Measurements to Investigate Impacts on Dusk-Side Electromagnetic Ion Cyclotron Waves
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:1
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Tidskriftsartikel (refereegranskat)abstract
- An extended interval of perturbed magnetospheric conditions in November 2016 supported increased convection and sunward transport of plasmaspheric material. During this period of time the Magnetospheric Multiscale satellites, with their apogees along Earth's dusk-side outer magnetosphere, encountered several cold plasma density structures at the same time as plasma bulk flows capable of accelerating hidden cold plasma occurred. Investigating the charged particle and fields data during two subintervals showed that the satellites made direct measurements of cold plasmaspheric ions embedded within multicomponent hot plasmas as well as electromagnetic emissions consistent with electromagnetic ion cyclotron (EMIC) waves. The complex in situ ion composition measurements were applied to linear wave modeling to interpret the impacts of cold and hot ion species on wave growth and band structure. Although the waves for both intervals were predicted to have peak growth rate below omega(He+), substantial differences were observed among all other dispersive properties. The modeling also showed EMIC waves generated in the presence of heavy ions had growth rates and unstable wave numbers always smaller than predicted for a pure proton-electron plasma. The results provide implications for future investigation of EMIC wave generation with and without direct measurements of the cold and hot plasma composition as well as of subsequent wave-particle interactions.
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20. |
- Lewis, Harry C., et al.
(författare)
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Magnetospheric Multiscale measurements of turbulent electric fields in earth's magnetosheath : How do plasma conditions influence the balance of terms in generalized Ohm's law?
- 2023
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 30:8
-
Tidskriftsartikel (refereegranskat)abstract
- Turbulence is ubiquitous within space plasmas, where it is associated with numerous nonlinear interactions. Magnetospheric Multiscale (MMS) provides the unique opportunity to decompose the electric field (E) dynamics into contributions from different linear and nonlinear processes via direct measurements of the terms in generalized Ohm's law. Using high-resolution multipoint measurements, we compute the magnetohydrodynamic ( E MHD ), Hall ( E Hall ), electron pressure ( E P e ), and electron inertia ( E inertia ) terms for 60 turbulent magnetosheath intervals, to uncover the varying contributions to the dynamics as a function of scale for different plasma conditions. We identify key spectral characteristics of the Ohm's law terms: the Hall scale, k Hall , where E Hall becomes dominant over E MHD ; the relative amplitude of E P e to E Hall , which is constant in the sub-ion range; and the relative scaling of the nonlinear and linear components of E MHD and of E Hall , which are independent of scale. We find expressions for the characteristics as a function of plasma conditions. The underlying relationship between turbulent fluctuation amplitudes and ambient plasma conditions is discussed. Depending on the interval, we observe that E MHD and E Hall can be dominated by either nonlinear or linear dynamics. We find that E P e is dominated by its linear contributions, with a tendency for electron temperature fluctuations to dominate at small scales. The findings are not consistent with existing linear kinetic Alfvén wave theory for isothermal fluctuations. Our work shows how contributions to turbulent dynamics change in different plasma conditions, which may provide insight into other turbulent plasma environments.
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21. |
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22. |
- Nakamura, Rumi, et al.
(författare)
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Structure of the Current Sheet in the 11 July 2017 Electron Diffusion Region Event
- 2019
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 124:2, s. 1173-1186
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the current sheet along the Magnetospheric Multiscale (MMS) orbit is examined during the 11 July 2017 Electron Diffusion Region (EDR) event. The location of MMS relative to the X-line is deduced and used to obtain the spatial changes in the electron parameters. The electron velocity gradient values are used to estimate the reconnection electric field sustained by nongyrotropic pressure. It is shown that the observations are consistent with theoretical expectations for an inner EDR in 2-D reconnection. That is, the magnetic field gradient scale, where the electric field due to electron nongyrotropic pressure dominates, is comparable to the gyroscale of the thermal electrons at the edge of the inner EDR. Our approximation of the MMS observations using a steady state, quasi-2-D, tailward retreating X-line was valid only for about 1.4 s. This suggests that the inner EDR is localized; that is, electron outflow jet braking takes place within an ion inertia scale from the X-line. The existence of multiple events or current sheet processes outside the EDR may play an important role in the geometry of reconnection in the near-Earth magnetotail. Plain Language Summary Magnetic reconnection is the process by which magnetic field lines coming from one region are broken and reconnected with magnetic field lines coming from another region. The simplest descriptions of magnetic reconnection are two dimensional, and a number of theoretical predictions have been made using the two-dimensional assumption. We study a magnetic reconnection event observed by the Magnetospheric Multiscale spacecraft on 11 July 2017 and find approximate agreement between the observations and the predictions of a two-dimensional model. The agreement includes the scale size of the reconnection region, details of the particle orbits, and the rate of reconnection.
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23. |
- Schwartz, Steven J., et al.
(författare)
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Ion Kinetics in a Hot Flow Anomaly : MMS Observations
- 2018
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 45:21, s. 11520-11529
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Tidskriftsartikel (refereegranskat)abstract
- Hot Flow Anomalies (HFAs) are transients observed at planetary bow shocks, formed by the shock interaction with a convected interplanetary current sheet. The primary interpretation relies on reflected ions channeled upstream along the current sheet. The short duration of HFAs has made direct observations of this process difficult. We employ high resolution measurements by NASA's Magnetospheric Multiscale Mission to probe the ion microphysics within a HFA. Magnetospheric Multiscale Mission data reveal a smoothly varying internal density and pressure, which increase toward the trailing edge of the HFA, sweeping up particles trapped within the current sheet. We find remnants of reflected or other backstreaming ions traveling along the current sheet, but most of these are not fast enough to out-run the incident current sheet convection. Despite the high level of internal turbulence, incident and backstreaming ions appear to couple gyro-kinetically in a coherent manner. Plain Language Summary Shock waves in space are responsible for energizing particles and diverting supersonic flows around planets and other obstacles. Explosive events known as Hot Flow Anomalies (HFAs) arise when a rapid change in the interplanetary magnetic field arrives at the bow shock formed by, for example, the supersonic solar wind plasma flow from the Sun impinging on the Earth's magnetic environment. HFAs are known to produce impacts all the way to ground level, but the physics responsible for their formation occur too rapidly to be resolved by previous satellite missions. This paper employs NASA's fleet of four Magnetospheric Multiscale satellites to reveal for the first time clear, discreet populations of ions that interact coherently to produce the extreme heating and deflection.
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24. |
- Sorriso-Valvo, Luca, et al.
(författare)
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Sign Singularity of the Local Energy Transfer in Space Plasma Turbulence
- 2019
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Ingår i: Frontiers in Physics. - : FRONTIERS MEDIA SA. - 2296-424X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- In weakly collisional space plasmas, the turbulent cascade provides most of the energy that is dissipated at small scales by various kinetic processes. Understanding the characteristics of such dissipative mechanisms requires the accurate knowledge of the fluctuations that make energy available for conversion at small scales, as different dissipation processes are triggered by fluctuations of a different nature. The scaling properties of different energy channels are estimated here using a proxy of the local energy transfer, based on the third-order moment scaling law for magnetohydrodynamic turbulence. In particular, the sign-singularity analysis was used to explore the scaling properties of the alternating positive-negative energy fluxes, thus providing information on the structure and topology of such fluxes for each of the different type of fluctuations. The results show the highly complex geometrical nature of the flux, and that the local contributions associated with energy and cross-helicity non-linear transfer have similar scaling properties. Consequently, the fractal properties of current and vorticity structures are similar to those of the Alfvenic fluctuations.
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25. |
- Witasse, O., et al.
(författare)
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Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto : Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 122:8, s. 7865-7890
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Tidskriftsartikel (refereegranskat)abstract
- We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116 degrees, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
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26. |
- Zhang, L. Q., et al.
(författare)
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Anisotropic Vorticity Within Bursty Bulk Flow Turbulence
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:10
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing Magnetospheric Multiscale (MMS) observation in the tail plasma sheet, we study the vorticity field (omega = del x V) of the plasma bulk (convective) velocity within the bursty bulk flow (BBF) in detailed. Two typical events are presented. In the event on 25 June 2017, E-y is the main component. In the other event on 6 July 2017, E-z is the main component. For both cases, the BBF electric field is dominated by the convective electric field (Ec = - V x B). Our case studies show clearly the existence of the convective vorticity field within the BBF. The vorticity field has prominent anisotropy (quantified by the anisotropic angle (theta aa = arctan(omega(perpendicular to)/omega(parallel to))). More often, the BBF omega field has stronger perpendicular vorticity (omega(perpendicular to)) than the parallel vorticity (omega(parallel to)). The dominance of vorticity by omega(perpendicular to)-dominating BBF is confirmed in the statistical sense. In particular, event on 25 June shows the significant evolution of the ion flux energy with the strength of the omega field. The strong omega field corresponds to the ion flux enhancement at high energy (above 10 keV), while the weak omega field corresponds to the ion flux enhancement at medium energy (2-5 keV). Investigation of the subset of channel from fast plasma investigation partial moment measurement reveals that the ion behaviors in the strong and decayed BBFs are distinctly different. The channeled ions form the narrow band distribution in the strong BBF but the multiple-layer distribution in the weak BBF. Finally, spectrum analysis indicates that the BBF omega(perpendicular to) and omega(parallel to) have a similar scaling about -2.0 (below 0.2 Hz).
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27. |
- Zhang, L. Q., et al.
(författare)
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First observation of fluid-like eddy-dominant bursty bulk flow turbulence in the Earth's tail plasma sheet
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Turbulence is a ubiquitous phenomenon in neutral and conductive fluids. According to classical theory, turbulence is a rotating flow containing vortices of different scales. Eddies play a fundamental role in the nonlinear cascade of kinetic energy at different scales in turbulent flow. In conductive fluids, the Alfvenic/kinetic Alfvenic wave (AW/KAW) is the new "cell" of magnetohydrodynamic (MHD) turbulence (frozen-in condition). Wave energy, which has equal kinetic and magnetic energy, is redistributed among multiple-scale Fourier modes and transferred from the large MHD scale to the small kinetic scale through the collision of counter-propagating Alfvenic wave packages propagating along the magnetic field line. Fluid-like eddy-dominant plasma flow turbulence has never been found in space since the launch of the first satellite in 1957. In this paper, we report the first observation of eddy-dominant turbulence within magnetic reconnection-generated fast flow in the Earth's tail plasma sheet by the Magnetospheric Multiscale Spacecraft (MMS). In eddy-dominant turbulent reconnection jet, ions dominate the flow field while electrons dominate current and magnetic fluctuations. Our findings shed new light on the nonlinear kinetic and magnetic energy cascade in MHD turbulence.
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28. |
- Andriopoulou, Maria, et al.
(författare)
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Plasma Density Estimates From Spacecraft Potential Using MMS Observations in the Dayside Magnetosphere
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:4, s. 2620-2629
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Tidskriftsartikel (refereegranskat)abstract
- Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emission as well as derive the plasma density information from spacecraft potential variations and active spacecraft potential control ion current. Such estimates are of particular importance especially during periods when the plasma instruments are not in operation and also when electron density observations with higher time resolution than the ones available from particle detectors are necessary. We compare the average photoelectron emission of different spacecraft and discuss their differences. We examine several time intervals when we performed our density estimations in order to understand the strengths and weaknesses of our data set. We finally compare our derived density estimates with the plasma density observations provided by plasma detectors onboard MMS, whenever available, and discuss the overall results. The estimated electron densities should only be used as a proxy of the electron density, complimentary to the plasma moments derived by plasma detectors, especially when the latter are turned off or when higher time resolution observations are required. While the derived data set can often provide valuable information about the plasma environment, the actual values may often be very far from the actual plasma density values and should therefore be used with caution.
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29. |
- Brolies, Thomas W., et al.
(författare)
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Rosetta observations of solar wind interaction with the comet 67P/Churyumov-Gerasimenko
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Rosetta spacecraft arrived at the comet 67P/Churyumov-Gerasimenko on August 6, 2014, which has made it possible to perform the first study of the solar wind interacting with the coma of a weakly outgassing comet. Aims. It is shown that the solar wind experiences large deflections (>45°) in the weak coma. The average ion velocity slows from the mass loading of newborn cometary ions, which also slows the interplanetary magnetic field (IMF) relative to the solar wind ions and subsequently creates a Lorentz force in the frame of the solar wind. The Lorentz force in the solar wind frame accelerates ions in the opposite direction of cometary pickup ion flow, and is necessary to conserve momentum. Methods. Data from the Ion and Electron Sensor are studied over several intervals of interest when significant solar wind deflection was observed. The deflections for protons and for He++ were compared with the flow of cometary pickup ions using the instrument's frame of reference. We then fit the data with a three-dimensional Maxwellian, and rotated the flow vectors into the Comet Sun Equatorial coordinate system, and compared the flow to the spacecraft's position and to the local IMF conditions. Results. Our observations show that the solar wind may be deflected in excess of 45° from the anti-sunward direction. Furthermore, the deflections change direction on a variable timescale. Solar wind protons are consistently more deflected than the He++. The deflections are not ordered by the spacecraft's position relative to the comet, but large changes in deflection are related to changes in the orthogonal IMF components
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30. |
- Dokgo, Kyunghwan, et al.
(författare)
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High-Frequency Wave Generation in Magnetotail Reconnection : Nonlinear Harmonics of Upper Hybrid Waves
- 2019
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 46:14, s. 7873-7882
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Tidskriftsartikel (refereegranskat)abstract
- MMS3 spacecraft passed the vicinity of the electron diffusion region of magnetotail reconnection on 3 July 2017, observing discrepancies between perpendicular electron bulk velocities and (E) over right arrow x (B) over right arrow drift, and agyrotropic electron crescent distributions. Analyzing linear wave dispersions, Burch et al. (2019, https://doi.org/10.1029/2019GL082471) showed the electron crescent generates high-frequency waves. We investigate harmonics of upper-hybrid (UH) waves using both observation and particle-in-cell (PIC) simulation, and the generation of electromagnetic radiation from PIC simulation. Harmonics of UH are linearly polarized and propagate along the perpendicular direction to the ambient magnetic field. Compared with two-dimensional PIC simulation and nonlinear kinetic theory, we show that the nonlinear beam-plasma interaction between the agyrotropic electrons and the core electrons generates harmonics of UH. Moreover, PIC simulation shows that agyrotropic electron beam can lead to electromagnetic (EM) radiation at the plasma frequency and harmonics.
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31. |
- Dokgo, Kyunghwan, et al.
(författare)
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High-Frequency Waves Driven by Agyrotropic Electrons Near the Electron Diffusion Region
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:5
-
Tidskriftsartikel (refereegranskat)abstract
- National Aeronautics and Space Administration's Magnetosphere Multiscale mission reveals that agyrotropic electrons and intense waves are prevalently present in the electron diffusion region. Prompted by two distinct Magnetosphere Multiscale observations, this letter investigates by theoretical means and the properties of agyrotropic electron beam-plasma instability and explains the origin of different structures in the wave spectra. The difference is owing to the fact that in one instance, a continuous beam mode is excited, while in the other, discrete Bernstein modes are excited, and the excitation of one mode versus the other depends on physical input parameters, which are consistent with observations. Analyses of dispersion relations show that the growing mode becomes discrete when the maximum growth rate is lower than the electron cyclotron frequency. Making use of particle-in-cell simulations, we found that the broadening angle Delta in the gyroangle space is also an important factor controlling the growth rate. Ramifications of the present finding are also discussed. Plain Language Summary Magnetospheric Multiscale mission has observed magnetic reconnection process, which converts magnetic energy to kinetic energy of charged particles. Extremely rapid time scale data reveal that electron scale high-frequency waves exist near the electron diffusion region of magnetic reconnection. Recently, two different types of waves observed; one is discrete electron-Bernstein waves, and the other is continuous beam modes. In this study, we formulated a unified theory for both types of waves. Comparing Magnetosphere Multiscale observations, the theory, and particle-in-cell simulations, this study shows that the same cause (agyrotropic electrons) can make two different wave structures depending on plasma parameters. The condition that the maximum growth rate of instabilities equals the electron cyclotron frequency can be considered as a threshold of the transition from discrete electron Bernstein waves to continuous beam modes.
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32. |
- Dokgo, Kyunghwan, et al.
(författare)
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The Effects of Upper-Hybrid Waves on Energy Dissipation in the Electron Diffusion Region
- 2020
-
Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:19
-
Tidskriftsartikel (refereegranskat)abstract
- Using a two-dimensional particle-in-cell simulation, we investigate the effects and roles of upper-hybrid waves (UHW) near the electron diffusion region (EDR). The energy dissipation via the wave-particle interaction in our simulation agrees withJ center dot E(')measured by magnetospheric multiscale (MMS) spacecraft. It means that UHW contributes to the local energy dissipation. As a result of wave-particle interactions, plasma parameters which determine the larger-scale energy dissipation in the EDR are changed. They-directional current decreases while the pressure tensorP(yz)increases/decreases when the agyrotropic beam density is low/high, where(x, y, z)-coordinates correspond the(L, M, N)-boundary coordinates. Because the reconnection electric field comes from- partial differential P-yz/ partial differential z, our result implies that UHW plays an additional role in affecting larger-scale energy dissipation in the EDR by changing plasma parameters. We provide a simple diagram that shows how the UHW activities change the profiles of plasma parameters near the EDR comparing cases with and without UHW.
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33. |
- Giagkiozis, Stefanos, et al.
(författare)
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Statistical Study of the Properties of Magnetosheath Lion Roars
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:7, s. 5435-5451
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Tidskriftsartikel (refereegranskat)abstract
- Lion roars are narrowband whistler wave emissions that have been observed in several environments, such as planetary magnetosheaths, the Earth's magnetosphere, the solar wind, downstream of interplanetary shocks, and the cusp region. We present measurements of more than 30,000 such emissions observed by the Magnetospheric Multiscale spacecraft with high-cadence (8,192 samples/s) search coil magnetometer data. A semiautomatic algorithm was used to identify the emissions, and an adaptive interval algorithm in conjunction with minimum variance analysis was used to determine their wave vector. The properties of the waves are determined in both the spacecraft and plasma rest frame. The mean wave normal angle, with respect to the background magnetic field (B-0), plasma bulk flow velocity (V-b), and the coplanarity plane (V-b x B-0) are 23 degrees, 56 degrees, and 0 degrees, respectively. The average peak frequencies were similar to 31% of the electron gyrofrequency (omega(ce)) observed in the spacecraft frame and similar to 18% of omega(ce) in the plasma rest frame. In the spacecraft frame, similar to 99% of the emissions had a frequency < omega(ce), while 98% had a peak frequency < 0.72 omega(ce) in the plasma rest frame. None of the waves had frequencies lower than the lower hybrid frequency, omega. From the probability density function of the electron plasma beta(e), the ratio between the electron thermal and magnetic pressure, similar to 99.6% of the waves were observed with beta(e) < 4 with a large narrow peak at 0.07 and two smaller, but wider, peaks at 1.26 and 2.28, while the average value was similar to 1.25.
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34. |
- Li, Jinxing, et al.
(författare)
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Local Excitation of Whistler Mode Waves and Associated Langmuir Waves at Dayside Reconnection Regions
- 2018
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:17, s. 8793-8802
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Tidskriftsartikel (refereegranskat)abstract
- In the Earth's dayside reconnection boundary layer, whistler mode waves coincide with magnetic field openings and the formation of the resultant anisotropic electrons. Depending on the energy range of anisotropic electrons, whistlers can grow at frequencies in the upper and/or lower band. Observations show that whistler mode waves modulate Langmuir wave amplitude as they propagate toward the X line. Observations of whistler mode wave phase and Langmuir waves packets, as well as coincident electron measurements, reveal that whistler mode waves can accelerate electrons via Landau resonance at locations where E(parallel to)is antiparallel to the wave propagation direction. The accelerated electrons produce localized beams, which subsequently drive the periodically modulated Langmuir waves. The close association of those two wave modes reveals the microscale electron dynamics in the exhaust region, and the proposed mechanism could potentially be applied to explain the modulation events observed in planetary magnetospheres and in the solar wind. Plain Language Summary The Sun's and Earth's magnetic field can merge and reconnect on dayside magnetopause. Using measurements from NASA's MMS spacecraft, we report that a class of electromagnetic wave, named whistler mode wave, coincides with the reconnected magnetic field lines. Besides, those whistlers are observed to modulate the electric field oscillations, known as Langmuir waves. Using high-resolution wave and particle measurements, we explain that the whistlers are locally excited when electrons from both sides of the magnetopause mix and form an unstable distribution. The modulated Langmuir waves are generated due to localized electron acceleration, which occurs when the velocity of electrons matches that of whistlers in the direction along the magnetic field. The whistler mode waves and associated Langmuir waves can be used as an additional tool to remotely sense the occurrence of magnetic reconnections.
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35. |
- Nilsson, Hans, et al.
(författare)
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Birth of a comet magnetosphere : A spring of water ions
- 2015
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 347:6220
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Tidskriftsartikel (refereegranskat)abstract
- The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (
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36. |
- Nilsson, Hans, et al.
(författare)
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Birth of a Magnetosphere
- 2021
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Ingår i: Magnetospheres in the Solar System. - : John Wiley & Sons. ; , s. 427-439, s. 427-439
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Bokkapitel (refereegranskat)abstract
- A magnetosphere may form around an object in a stellar wind either due to the intrinsic magnetic field of the object or stellar wind interaction with the ionosphere of the object. Comets represent the most variable magnetospheres in our solar system, and through the Rosetta mission we have had the chance to study the birth and evolution of a comet magnetosphere as the comet nucleus approached the Sun. We review the birth of the comet magnetosphere as observed at comet 67P Churyumov–Gerasimenko, the formation of plasma boundaries and how the solar wind–atmosphere interaction changes character as the cometary gas cloud and magnetosphere grow in size. Mass loading of the solar wind leads to an asymmetric deflection of the solar wind for low outgassing rates. With increasing activity a solar wind ion cavity forms. Intermittent shock‐like features were also observed. For intermediate outgassing rate a diamagnetic cavity is formed inside the solar wind ion cavity, thus well separated from the solar wind. The cometary plasma was typically very structured and variable. The region of the coma dense enough to have significant collisions forms a special region with different ion chemistry and plasma dynamics as compared to the outer collision‐free region.
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37. |
- Pan, Dong-Xiao, et al.
(författare)
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Rippled Electron-Scale Structure of a Dipolarization Front
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:22, s. 12116-12124
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Tidskriftsartikel (refereegranskat)abstract
- We use the Magnetospheric Multiscale mission to investigate electron-scale structures at a dipolarization front. The four spacecraft are separated by electron scales and observe large differences in plasma and field parameters within the dipolarization front, indicating strong deviation from typically assumed plane or slightly curved front surface. We attribute this to ripples generated by the lower hybrid drift instability (LHDI) with wave number of k(rho e)similar or equal to 0.4 and maximum wave potential of similar to 1 kV similar to k(B)T(e). Power law-like spectra of E-perpendicular to with slope of -3 indicates the turbulent cascade of LHDI. LHDI is observed together with bursty high-frequency parallel electric fields, suggesting coupling of LHDI to higher-frequency electrostatic waves. Plain Language Summary Dipolarization fronts (DFs) are narrow boundaries with sharp enhancement of magnetic field, located at the leading part of fast plasma jets observed in Earth's magnetotail. DFs are typically assumed to be smooth boundaries at scales comparable to the ion gyroradius and below. In this study, we use the four Magnetospheric Multiscale spacecraft separated by several electron gyroradii to investigate fine structure of a DF. Surprisingly, we observe significant differences in the fields and plasma measurements between the spacecraft despite their small separation. We attribute these signatures to electron-scale disturbances propagating along the DF surface, and thus the DF surface is not smooth as expected but rather rippled. The ripples develop as a result of a plasma instability driven by the strong inhomogeneities present at the DF. The fact that the ripples have such small scales means that they can effectively interact with plasma electrons.
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38. |
- Toledo-Redondo, Sergio, et al.
(författare)
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Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 122:9, s. 9396-9413
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Tidskriftsartikel (refereegranskat)abstract
- Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10-25% of the energy spent by reconnection into ion heating went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely helium and oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization. Plain Language Summary The magnetic field of Earth creates a natural shield that isolates and protects us from the particles and fields coming from our star, the Sun. This natural shield is called the magnetosphere and is filled by plasma. The particles coming from the Sun form another plasma called the solar wind and are usually deviated around the magnetosphere. However, under certain circumstances these two plasmas can reconnect (magnetic reconnection), and part of the energy and mass of the two plasmas is interchanged. Magnetic reconnection is the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs to particles of very low energy (cold ions) of ionospheric origin when they reach the reconnecting boundary of the magnetosphere. It is found that they are energized and take an important part of the energy spent in reconnecting the plasmas. The plasma boundary develops spatial structures and emits waves that are able to heat the cold ions. Once heated, these cold ions irreversibly will escape the Earth's magnetosphere to never come back to Earth.
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39. |
- Toledo-Redondo, Sergio, et al.
(författare)
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Perpendicular Current Reduction Caused by Cold Ions of Ionospheric Origin in Magnetic Reconnection at the Magnetopause : Particle-in-Cell Simulations and Spacecraft Observations
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:19, s. 10033-10042
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Tidskriftsartikel (refereegranskat)abstract
- Cold ions of ionospheric origin are present throughout the Earth's magnetosphere, including the dayside magnetopause, where they modify the properties of magnetic reconnection, a major coupling mechanism at work between the magnetosheath and the magnetosphere. We present Magnetospheric MultiScale (MMS) spacecraft observations of the reconnecting magnetopause with different amounts of cold ions and show that their presence reduces the Hall term in the Ohm's law. Then, we compare two particle-in-cell simulations, with and without cold ions on the magnetospheric side. The cold ions remain magnetized inside the magnetospheric separatrix region, leading to the reduction of the perpendicular currents associated with the Hall effect. Moreover, this reduction is proportional to the relative number density of cold ions. And finally, the Hall electric field peak is reduced along the magnetospheric separatrix owing to cold ions. This should have an effect on energy conversion by reconnection from electromagnetic fields to kinetic energy of the particles. Plain Language Summary The magnetic field of Earth creates a natural boundary that isolates and protects us from the particles and fields coming from the Sun, typically known as the solar wind. This natural shield is called the magnetosphere and is filled by plasma. The particles are coming from the solar wind and are usually deviated around the magnetosphere. However, various mechanisms are capable of interconnecting these two regions of plasma, permitting the exchange of mass and energy. Magnetic reconnection is a primary coupling mechanism and the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs when particles of very low energy (cold ions) of ionospheric origin reach the reconnecting boundary between the solar wind and the magnetosphere. We use both spacecraft observations and numerical simulations, and we find that they modify the way reconnection operates, by reducing the currents carried by electrons. The electric fields associated with energization of particles are reduced as well under the presence of cold ions coming from the ionosphere.
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40. |
- Wang, Shan, et al.
(författare)
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Whistler Waves Associated With Electron Beams in Magnetopause Reconnection Diffusion Regions
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:9
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Tidskriftsartikel (refereegranskat)abstract
- Whistler waves are often observed in magnetopause reconnection associated with electron beams. We analyze seven MMS crossings surrounding the electron diffusion region (EDR) to study the role of electron beams in whistler excitation. Waves have two major types: (a) Narrow-band waves with high ellipticities and (b) broad-band waves that are more electrostatic with significant variations in ellipticities and wave normal angles. While both types of waves are associated with electron beams, the key difference is the anisotropy of the background population, with perpendicular and parallel anisotropies, respectively. The linear instability analysis suggests that the first type of wave is mainly due to the background anisotropy, with the beam contributing additional cyclotron resonance to enhance the wave growth. The second type of broadband waves are excited via Landau resonance, and as seen in one event, the beam anisotropy induces an additional cyclotron mode. The results are supported by particle-in-cell simulations. We infer that the first type occurs downstream of the central EDR, where background electrons experience Betatron acceleration to form the perpendicular anisotropy; the second type occurs in the central EDR of guide field reconnection. A parametric study is conducted with linear instability analysis. A beam anisotropy alone of above similar to 3 likely excites the cyclotron mode waves. Large beam drifts cause Doppler shifts and may lead to left-hand polarizations in the ion frame. Future studies are needed to determine whether the observation covers a broader parameter regime and to understand the competition between whistler and other instabilities.
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