| 1. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 2. |
- Niemi, MEK, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 3. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 4. |
- Murari, A., et al.
(författare)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Arndt, D. S., et al.
(författare)
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STATE OF THE CLIMATE IN 2017
- 2018
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 99:8, s. S1-S310
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Forskningsöversikt (refereegranskat)
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| 9. |
- Hudson, Lawrence N, et al.
(författare)
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The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
- 2017
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
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Tidskriftsartikel (refereegranskat)abstract
- The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
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| 10. |
- Kattge, Jens, et al.
(författare)
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TRY plant trait database - enhanced coverage and open access
- 2020
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Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 26:1, s. 119-188
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Tidskriftsartikel (refereegranskat)abstract
- Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.
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| 11. |
- Grossmann, Igor, et al.
(författare)
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Insights into the accuracy of social scientists' forecasts of societal change
- 2023
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Ingår i: Nature Human Behaviour. - : Springer Nature. - 2397-3374. ; 7, s. 484-501
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Tidskriftsartikel (refereegranskat)abstract
- How well can social scientists predict societal change, and what processes underlie their predictions? To answer these questions, we ran two forecasting tournaments testing the accuracy of predictions of societal change in domains commonly studied in the social sciences: ideological preferences, political polarization, life satisfaction, sentiment on social media, and gender-career and racial bias. After we provided them with historical trend data on the relevant domain, social scientists submitted pre-registered monthly forecasts for a year (Tournament 1; N = 86 teams and 359 forecasts), with an opportunity to update forecasts on the basis of new data six months later (Tournament 2; N = 120 teams and 546 forecasts). Benchmarking forecasting accuracy revealed that social scientists' forecasts were on average no more accurate than those of simple statistical models (historical means, random walks or linear regressions) or the aggregate forecasts of a sample from the general public (N = 802). However, scientists were more accurate if they had scientific expertise in a prediction domain, were interdisciplinary, used simpler models and based predictions on prior data. How accurate are social scientists in predicting societal change, and what processes underlie their predictions? Grossmann et al. report the findings of two forecasting tournaments. Social scientists' forecasts were on average no more accurate than those of simple statistical models.
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| 12. |
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| 13. |
- Chen, H.Y., et al.
(författare)
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Dyslipidemia, inflammation, calcification, and adiposity in aortic stenosis: a genome-wide study
- 2023
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Ingår i: European Heart Journal. - : Oxford University Press. - 0195-668X .- 1522-9645. ; 44:21, s. 1927-1939
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Tidskriftsartikel (refereegranskat)abstract
- Aims Although highly heritable, the genetic etiology of calcific aortic stenosis (AS) remains incompletely understood. The aim of this study was to discover novel genetic contributors to AS and to integrate functional, expression, and cross-phenotype data to identify mechanisms of AS. Methods and results A genome-wide meta-analysis of 11.6 million variants in 10 cohorts involving 653 867 European ancestry participants (13 765 cases) was performed. Seventeen loci were associated with AS at P ≤ 5 × 10−8, of which 15 replicated in an independent cohort of 90 828 participants (7111 cases), including CELSR2–SORT1, NLRP6, and SMC2. A genetic risk score comprised of the index variants was associated with AS [odds ratio (OR) per standard deviation, 1.31; 95% confidence interval (CI), 1.26–1.35; P = 2.7 × 10−51] and aortic valve calcium (OR per standard deviation, 1.22; 95% CI, 1.08–1.37; P = 1.4 × 10−3), after adjustment for known risk factors. A phenome-wide association study indicated multiple associations with coronary artery disease, apolipoprotein B, and triglycerides. Mendelian randomization supported a causal role for apolipoprotein B-containing lipoprotein particles in AS (OR per g/L of apolipoprotein B, 3.85; 95% CI, 2.90–5.12; P = 2.1 × 10−20) and replicated previous findings of causality for lipoprotein(a) (OR per natural logarithm, 1.20; 95% CI, 1.17–1.23; P = 4.8 × 10−73) and body mass index (OR per kg/m2, 1.07; 95% CI, 1.05–1.9; P = 1.9 × 10−12). Colocalization analyses using the GTEx database identified a role for differential expression of the genes LPA, SORT1, ACTR2, NOTCH4, IL6R, and FADS. Conclusion Dyslipidemia, inflammation, calcification, and adiposity play important roles in the etiology of AS, implicating novel treatments and prevention strategies. © The Author(s) 2023. Published by Oxford University Press on behalf of the European Society of Cardiology.
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| 14. |
- Jung, Christian, et al.
(författare)
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A comparison of very old patients admitted to intensive care unit after acute versus elective surgery or intervention
- 2019
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Ingår i: Journal of critical care. - : W B SAUNDERS CO-ELSEVIER INC. - 0883-9441 .- 1557-8615. ; 52, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- Background: We aimed to evaluate differences in outcome between patients admitted to intensive care unit (ICU) after elective versus acute surgery in a multinational cohort of very old patients (80 years; VIP). Predictors of mortality, with special emphasis on frailty, were assessed.Methods: In total, 5063 VIPs were induded in this analysis, 922 were admitted after elective surgery or intervention, 4141 acutely, with 402 after acute surgery. Differences were calculated using Mann-Whitney-U test and Wilcoxon test. Univariate and multivariable logistic regression were used to assess associations with mortality.Results: Compared patients admitted after acute surgery, patients admitted after elective surgery suffered less often from frailty as defined as CFS (28% vs 46%; p < 0.001), evidenced lower SOFA scores (4 +/- 5 vs 7 +/- 7; p < 0.001). Presence of frailty (CFS >4) was associated with significantly increased mortality both in elective surgery patients (7% vs 12%; p = 0.01), in acute surgery (7% vs 12%; p = 0.02).Conclusions: VIPs admitted to ICU after elective surgery evidenced favorable outcome over patients after acute surgery even after correction for relevant confounders. Frailty might be used to guide clinicians in risk stratification in both patients admitted after elective and acute surgery.
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| 15. |
- Seth-Smith, Helena M. B., et al.
(författare)
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Whole-genome sequences of Chlamydia trachomatis directly from clinical samples without culture
- 2013
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Ingår i: Genome Research. - : Cold Spring Harbor Laboratory Press (CSHL). - 1088-9051 .- 1549-5469. ; 23:5, s. 855-866
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Tidskriftsartikel (refereegranskat)abstract
- The use of whole-genome sequencing as a tool for the study of infectious bacteria is of growing clinical interest. Chlamydia trachomatis is responsible for sexually transmitted infections and the blinding disease trachoma, which affect hundreds of millions of people worldwide. Recombination is widespread within the genome of C. trachomatis, thus whole-genome sequencing is necessary to understand the evolution, diversity, and epidemiology of this pathogen. Culture of C trachomatis has, until now, been a prerequisite to obtain DNA for whole-genome sequencing; however, as C trachomatis is an obligate intracellular pathogen, this procedure is technically demanding and time consuming. Discarded clinical samples represent a large resource for sequencing the genomes of pathogens, yet clinical swabs frequently contain very low levels of C trachomatis DNA and large amounts of contaminating microbial and human DNA. To determine whether it is possible to obtain whole-genome sequences from bacteria without the need for culture, we have devised an approach that combines immunomagnetic separation (IMS) for targeted bacterial enrichment with multiple displacement amplification (MDA) for whole-genome amplification. Using IMS-MDA ill conjunction with high-throughput multiplexed Illumina sequencing, we have produced the first whole bacterial genome sequences direct from clinical samples. We also show that this method can be used to generate genome data from nonviable archived samples. This method will prove a useful tool in answering questions relating to the biology of many difficult-to-culture or fastidious bacteria of clinical concern.
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| 16. |
- Ball, W. T., et al.
(författare)
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The Upper Stratospheric Solar Cycle Ozone Response
- 2019
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 46:3, s. 1831-1841
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Tidskriftsartikel (refereegranskat)abstract
- The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1-10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data-merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U-shaped spatial structure with lobes emanating from the tropics (5-10 hPa) to high altitudes at midlatitudes (1-3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASIC(v2) ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used. Plain Language Summary Changes in the output of the Sun are thought to influence surface weather and climate through a set of processes initiated by the enhancement of upper stratosphere (32-48 km) ozone. In order to understand and assess the solar impact on the climate system, it is important that models reproduce the observed solar signal. However, the recommended data set for comparison with climate models remains disputed. We use newly improved observed ozone composites to determine both why there is disagreement between composites and which is most likely to be correct. We find that artifact-corrected composites represent the response better than those based on SBUV data alone. Further, we identify a U-shaped spatial structure with lobes emanating from the tropics to high altitudes at midlatitudes. An idealized chemistry climate model experiment and simulations considering historical meteorological conditions both support this conclusion. The results are of benefit to satellite-instrument scientists and to those engaged in atmospheric and climate research using both observations and climate models. The results will be important for assessing the solar signal in currently active and future assessments of chemistry climate models (e.g., Chemistry-Climate Model Initiative). We recommend the BASICv2 ozone composite to best represent historical upper stratospheric variability.
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| 17. |
- Hendrickx, Koen, et al.
(författare)
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Production and transport mechanisms of NO in observations and models
- 2018
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:12, s. 9075-9089
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Tidskriftsartikel (refereegranskat)abstract
- A reservoir of Nitric Oxide (NO) in the lower thermosphere efficiently cools the atmosphere after periods of enhanced geomagnetic activity. Transport from this reservoir to the stratosphere within the winter polar vortex allows NO to deplete ozone levels and thereby affect the middle atmospheric heat budget. As more climate models resolve the mesosphere and lower thermosphere (MLT) region, the need for an improved representation of NO related processes increases. This work presents a detailed comparison of NO in the Antarctic MLT region between observations made by the Solar Occultation for Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite and simulations performed by the Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM). We investigate 7 years of SOFIE observations and focus on the Southern hemisphere, rather than on dynamical variability in the Northern hemisphere or a specific geomagnetic perturbed event. The morphology of the simulated NO is in agreement with observations though the long term mean is too high and the short term variability is too low. Number densities are more similar during winter, though the altitude of peak densities, which reaches between 102–106 km in WACCM and between 98–104 km in SOFIE, is most separated during winter. Using multiple linear regressions and superposed epoch analyses we investigate how well the NO production and transport are represented in the model. The impact of geomagnetic activity is shown to drive NO variations in the lower thermosphere similarly across both datasets. The dynamical transport from the lower thermosphere into the mesosphere during polar winter is found to agree very well, with a descent rate of about 2.2 km/day in the 80–110 km region in both datasets. The downward transported NO fluxes are however too low in WACCM, which is likely due to medium energy electrons and D-region chemistry that are not represented in the model.
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| 18. |
- Hendrickx, Koen, et al.
(författare)
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Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere
- 2017
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 44:19, s. 10081-10087
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Tidskriftsartikel (refereegranskat)abstract
- Nitric oxide (NO) observations from the Solar Occultation for Ice Experiment and Student Nitric Oxide Explorer satellite instruments are investigated to determine the relative importance of drivers of short-term NO variability. We study the variations of deseasonalized NO anomalies by removing a climatology, which explains between approximately 70% and 90% of the total NO budget, and relate them to variability in geomagnetic activity and solar radiation. Throughout the lower thermosphere geomagnetic activity is the dominant process at high latitudes, while in the equatorial region solar radiation is the primary source of short-term NO changes. Consistent results are obtained on estimated geomagnetic and radiation contributions of NO variations in the two data sets, which are nearly a decade apart in time. The analysis presented here can be applied to model simulations of NO to investigate the accuracy of the parametrized physical drivers.
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| 19. |
- Lossow, Stefan, 1977-
(författare)
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Observations of water vapour in the middle atmosphere
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water vapour is the most important greenhouse gas and plays a fundamental role in the climate system and for the chemistry of the Earth's atmosphere. This thesis presents observations of water vapour in the middle atmosphere with a particular focus on the mesosphere. The majority of these observations presented in this thesis have been performed by the Swedish satellite Odin, providing global observations since 2001. Further observations come from the Hygrosonde-2 campaign in December 2001 based on balloon and rocket-borne measurements. A general overview of Odin's water vapour measurements in the middle atmosphere is given. The optimisation of the mesospheric water vapour retrieval is presented in detail.The analysis of the observations has focused mainly on different dynamical aspects utilising the characteristic of water vapour as a dynamical tracer in the middle atmosphere. One application is the mesospheric part of the semi-annual oscillation (SAO). The observations reveal that this oscillation is the dominant pattern of variability between 30°S and 10°N in the mesosphere up to an altitude of 80 km. Above 90 km the SAO is dominating at all latitudes in the tropics and subtropics. It is shown that the SAO exhibits a distinct phase change between 75 km and 80 km in the tropical region.This thesis also presents the first satellite observations of water vapour in the altitude range between 90 km and 110 km, extending the observational database up into the lower thermosphere. In the polar regions water vapour exhibits the annual maximum during winter time above 95 km, mainly caused by upwelling during this season. This behaviour is different from that observed in the subjacent part of the mesosphere where the annual maximum occurs during summer time.The Hygrosonde-2 campaign provided a high resolution measurement of water vapour in the vicinity of the polar vortex edge. This edge prevents horizontal transport causing different water vapour characteristics inside and outside the polar vortex. The observations show that this separating behaviour extends high up into the mesosphere. Small scale transitions in the Hygrosonde-2 profile between conditions inside and outside the vortex coincided with wind shears caused by gravity waves.
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| 20. |
- Plane, John M. C., et al.
(författare)
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Opinion : Recent developments and future directions in studying the mesosphere and lower thermosphere
- 2023
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Ingår i: Atmospheric Chemistry And Physics. - 1680-7316 .- 1680-7324. ; 23:20, s. 13255-13282
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Forskningsöversikt (refereegranskat)abstract
- This article begins with a review of important advances in the chemistry and related physics of the mesosphere and lower thermosphere (MLT) region of the atmosphere that have occurred over the past 2 decades, since the founding of Atmospheric Chemistry and Physics. The emphasis here is on chemistry, but we also discuss recent findings on atmospheric dynamics and forcings to the extent that these are important for understanding MLT composition and chemistry. Topics that are covered include observations, with satellite, rocket and ground-based techniques; the variability and connectedness of the MLT on various length scales and timescales; airglow emissions; the cosmic dust input and meteoric metal layers; and noctilucent/polar mesospheric ice clouds. The paper then concludes with a discussion of important unanswered questions and likely future directions for the field over the next decade.
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| 21. |
- Rapp, Markus, et al.
(författare)
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Rocket-borne in situ measurements of meteor smoke : Charging properties and implications for seasonal variation
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. D00I16-
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Tidskriftsartikel (refereegranskat)abstract
- Rocket-borne observations of meteoric smoke particles (MSPs) are presented from three campaigns at polar latitudes (69 degrees N) in September 2006, and in the summers of 2007 and 2008. MSPs are detected using a novel technique based on photoelectron emission from the particles after stimulation by UV photons emitted by a xenon flashlamp. Resulting photoelectron currents are shown to be proportional to particle volume density. September results match model predictions qualitatively at altitudes from 65 to 85 km while measurements at higher altitudes are contaminated by photoelectrons from NO and O-2((1)Delta(g)). Contamination below this altitude can be excluded based on concurrent satellite observations. The observations show a large variability from flight to flight. Part of this variability can be attributed to differences in the charging of MSPs during day and night. Finally we find that MSP volume density in summer can exceed that during September. Analyzing model simulations of the global transport and microphysics of these particles, we show that our observations are in agreement with the model predictions, even though number densities of particles with radii >1 nm, which have long been thought to be suitable condensation nuclei for mesospheric ice particles, show the opposite behavior. It is shown that this discrepancy is caused by the fact that even larger particles (similar to 3 nm) dominate the volume density and that transport affects these different particle sizes in different ways. These results reinforce previous model findings according to which seasonal MSP variability is mainly driven by the global circulation and corresponding transport.
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| 22. |
- Siskind, David E., et al.
(författare)
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Decreases in atomic hydrogen over the summer pole : Evidence for dehydration from polar mesospheric clouds?
- 2008
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:13
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Tidskriftsartikel (refereegranskat)abstract
- Observations from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) instrument on the NASA/Thermospheric Ionosphere Mesosphere Energetics and Dynamics satellite show a surprising decrease in the inferred atomic hydrogen (H) over the polar regions in the lowermost thermosphere during the summer. This contrasts with predictions by global models that H should peak in this region at this time. We suggest the decrease is a consequence of the sequestering of the water vapor by the formation of polar mesospheric clouds (PMCs) that redistributes the H2O thus reducing the chemical source of H. This decrease is more pronounced in the Northern rather than the Southern summer which is roughly consistent with the known morphology of PMCs. A model calculation which includes a PMC parameterization gives good qualitative agreement with the data suggesting that this process should be considered in global models of the coupling between the middle and upper atmosphere. Copyright 2008 by the American Geophysical Union.
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| 23. |
- Smith, Anne K., et al.
(författare)
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Satellite observations of high nighttime ozone at the equatorial mesopause
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:17
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Tidskriftsartikel (refereegranskat)abstract
- Measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument enable the characterization of the seasonal variation of ozone and temperature in the upper mesosphere. These are the first global measurements that resolve both the structure of the secondary ozone maximum at night and the temperature over all seasons of the year. The average nighttime mixing ratios at the altitude of the maximum vary with latitude and season. Analysis shows that the highest mixing ratios are clustered near the equator during equinoxes. The high ozone mixing ratios are observed in exactly the place and time at which the diurnal tide is largest. The diurnal tidal phase is such that coldest temperatures at 95 km occur near midnight. The high ozone is coincident with regions that have both low temperature and low amounts of atomic hydrogen. We focus particularly on ozone mixing ratios in the range of 18-50 ppmv; these occur intermittently in the equinoctial tropics on days when the night temperature is particularly cold. The occurrence of ozone maxima over 20 ppmv was unexpected but is shown in this paper to be consistent with theory and is a result of large-amplitude diurnal tides. The same seasonal and latitudinal characteristics are seen in ozone density measured by Global Ozone Monitoring by Occultation of Stars. Copyright 2008 by the American Geophysical Union.
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| 24. |
- Smith-Johnsen, Christine, et al.
(författare)
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Nitric Oxide Response to the April 2010 Electron Precipitation Event : Using WACCM and WACCM-D With and Without Medium-Energy Electrons
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:6, s. 5232-5245
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Tidskriftsartikel (refereegranskat)abstract
- Energetic electrons from the magnetosphere deposit their energy in the atmosphere and lead to production of nitric oxide (NO) in the mesosphere and lower thermosphere. We study the atmospheric NO response to a geomagnetic storm in April 2010 with WACCM (Whole Atmosphere Community Climate Model). Modeled NO is compared to observations by Solar Occultation For Ice Experiment/Aeronomy of Ice in the Mesosphere at 72-82 degrees S latitudes. We investigate the modeled NOs sensitivity to changes in energy and chemistry. The electron energy model input is either a parameterization of auroral electrons or a full range energy spectrum (1-750keV) from National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and European Organisation for the Exploitation of Meteorological Satellites/Meteorological Operational satellites. To study the importance of ion chemistry for the production of NO, WACCM-D, which has more complex ion chemistry, is used. Both standard WACCM and WACCM-D underestimate the storm time NO increase in the main production region (90-110km), using both electron energy inputs. At and below 80km, including medium-energy electrons (>30keV) is important both for NO directly produced at this altitude region and for NO transported from other regions (indirect effect). By using WACCM-D the direct NO production is improved, while the indirect effects on NO suffer from the downward propagating deficiency above. In conclusion, both a full range energy spectrum and ion chemistry is needed throughout the mesosphere and lower thermosphere region to increase the direct and indirect contribution from electrons on NO.
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| 25. |
- Tilmes, Simone, et al.
(författare)
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The hydrological impact of geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP)
- 2013
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-897X. ; 118:19, s. 11036-11058
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Tidskriftsartikel (refereegranskat)abstract
- The hydrological impact of enhancing Earth's albedo by solar radiation management is investigated using simulations from 12 Earth System models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). We contrast an idealized experiment, G1, where the global mean radiative forcing is kept at preindustrial conditions by reducing insolation while the CO2 concentration is quadrupled to a 4×CO2 experiment. The reduction of evapotranspiration over land with instantaneously increasing CO2 concentrations in both experiments largely contributes to an initial reduction in evaporation. A warming surface associated with the transient adjustment in 4×CO2 generates an increase of global precipitation by around 6.9% with large zonal and regional changes in both directions, including a precipitation increase of 10% over Asia and a reduction of 7% for the North American summer monsoon. Reduced global evaporation persists in G1 with temperatures close to preindustrial conditions. Global precipitation is reduced by around 4.5%, and significant reductions occur over monsoonal land regions: East Asia (6%), South Africa (5%), North America (7%), and South America (6%). The general precipitation performance in models is discussed in comparison to observations. In contrast to the 4×CO2 experiment, where the frequency of months with heavy precipitation intensity is increased by over 50% in comparison to the control, a reduction of up to 20% is simulated in G1. These changes in precipitation in both total amount and frequency of extremes point to a considerable weakening of the hydrological cycle in a geoengineered world.
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| 26. |
- Yu, Bingkun, et al.
(författare)
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Comparison of middle- and low-latitude sodium layer from a ground-based lidar network, the Odin satellite, and WACCM–Na model
- 2022
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 22:17, s. 11485-11504
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Tidskriftsartikel (refereegranskat)abstract
- The ground-based measurements obtained from a lidar network and the 6-year OSIRIS (optical spectrograph and infrared imager system) limb-scanning radiance measurements made by the Odin satellite are used to study the climatology of the middle- and low-latitude sodium (Na) layer. Up to January 2021, four Na resonance fluorescence lidars at Beijing (40.5∘ N, 116.0∘ E), Hefei (31.8∘ N, 117.3∘ E), Wuhan (30.5∘ N, 114.4∘ E), and Haikou (19.5∘ N, 109.1∘ E) collected vertical profiles of Na density for a total of 2136 nights (19 587 h). These large datasets provide multi-year routine measurements of the Na layer with exceptionally high temporal and vertical resolution. The lidar measurements are particularly useful for filling in OSIRIS data gaps since the OSIRIS measurements were not made during the dark winter months because they utilize the solar-pumped resonance fluorescence from Na atoms. The observations of Na layers from the ground-based lidars and the satellite are comprehensively compared with a global model of meteoric Na in the atmosphere (WACCM–Na). The lidars present a unique test of OSIRIS and WACCM (Whole Atmosphere Community Climate Model), because they cover the latitude range along 120∘ E longitude in an unusual geographic location with significant gravity wave generation. In general, good agreement is found between lidar observations, satellite measurements, and WACCM simulations. On the other hand, the Na number density from OSIRIS is larger than that from the Na lidars at the four stations within one standard deviation of the OSIRIS monthly average, particularly in autumn and early winter arising from significant uncertainties in Na density retrieved from much less satellite radiance measurements. WACCM underestimates the seasonal variability of the Na layer observed at the lower latitude lidar stations (Wuhan and Haikou). This discrepancy suggests the seasonal variability of vertical constituent transport modelled in WACCM is underestimated because much of the gravity wave spectrum is not captured in the model.
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