| 1. |
|
|
| 2. |
- Akiyama, Kazunori, et al.
(författare)
-
First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
- 2019
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of similar to 40 mu as, consistent with the size and shape of the lensed photon orbit encircling the "shadow" of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others' work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.
|
|
| 3. |
- Akiyama, Kazunori, et al.
(författare)
-
First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
- 2019
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
-
Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.
|
|
| 4. |
- Akiyama, Kazunori, et al.
(författare)
-
First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
- 2019
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 +/- 3 mu as and constrain its fractional width to be
|
|
| 5. |
- Porth, Oliver, et al.
(författare)
-
The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project
- 2019
-
Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 243:2
-
Tidskriftsartikel (refereegranskat)abstract
- Recent developments in compact object astrophysics, especially the discovery of merging neutron stars by LIGO, the imaging of the black hole in M87 by the Event Horizon Telescope, and high- precision astrometry of the Galactic Center at close to the event horizon scale by the GRAVITY experiment motivate the development of numerical source models that solve the equations of general relativistic magnetohydrodynamics (GRMHD). Here we compare GRMHD solutions for the evolution of a magnetized accretion flow where turbulence is promoted by the magnetorotational instability from a set of nine GRMHD codes: Athena++, BHAC, Cosmos++, ECHO, H-AMR, iharm3D, HARM-Noble, IllinoisGRMHD, and KORAL. Agreement among the codes improves as resolution increases, as measured by a consistently applied, specially developed set of code performance metrics. We conclude that the community of GRMHD codes is mature, capable, and consistent on these test problems.
|
|
| 6. |
- Cameron, David Lansing, et al.
(författare)
-
A comparative study of special educator preparation in Norway and Sweden
- 2018
-
Ingår i: British Journal of Special Education. - : Wiley. - 0952-3383 .- 1467-8578. ; 45:3, s. 256-276
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to explore similarities and differences between special educator preparation in Norway and in Sweden. Graduates of special education programmes at two Norwegian (n = 320) and two Swedish universities (n = 425) who completed their training between 2001 and 2012 responded to surveys. Findings indicate that both Swedish and Norwegian graduates felt prepared for their current work and that teaching approaches employed in the different programmes were similar. However, there appears to be a stronger focus on pupils’ social goals in Sweden, as well as on advising teachers, school development and promoting inclusive environments. In contrast, Norwegian participants reported a greater focus on preparation to work with specific types of learning and behavioural difficulties. Findings are discussed in relation to differing political and social structures, such as national regulations for steering special educator preparation in Sweden, which are absent in the Norwegian context.
|
|
| 7. |
- Briggs, Joseph S., et al.
(författare)
-
Windfall gains and stock market participation
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We estimate the causal effect of wealth on stock market participation using administrative data on Swedish lottery players. A $150,000 windfall gain increases stock ownership probability among pre-lottery non-participants by 12 percentage points, while pre-lottery stock holders are unaffected. The effect is immediate, seemingly permanent and heterogeneous in intuitive ways. Standard lifecycle models predict wealth effects far too large to match our causal estimates under common calibrations. Additional analyses suggest a limited role for explanations such as procrastination or real-estate investment. Overall, results suggest that “nonstandard” beliefs or preferences contribute to the nonparticipation of households across many demographic groups.
|
|
| 8. |
- Briggs, Joseph, et al.
(författare)
-
Wealth and Stock Market Participation : Estimating the Causal Effect From Swedish Lotteries
- 2015
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we estimate the causal effect of wealth on stock market participation. The positive cross-sectional relationship between participation and wealth is well-established, with previous work suggesting that moderate costs of stock market participation are capable of rationalizing the decision of most non-participants. In our study we use a large sample of Swedish lottery players whom were randomly assigned over 1 billion USD, linked to administrative tax records of asset holdings, to precisely identify both the effect of wealth and the costs necessary to explain non-participation. Although we estimate a positive effect of wealth on participation, our estimate is much smaller than that implied by the cross-section. Furthermore, our estimates of participation costs are 10-20 times higher than those proposed in previous studies. We interpret these results within a structural model of life-cycle stock market participation, and use participation responses following random wealth assignment to estimate entry and participation costs conditional on a variety of demographic and individual characteristics. We conclude that it is unlikely that fixed financial costs are credible explanations for equity market non-participation.
|
|
| 9. |
- Cesarini, David, et al.
(författare)
-
Replication data for : The Effect of Wealth on Individual and Household Labor Supply: Evidence from Swedish Lotteries
- 2017
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We study the effect of wealth on labor supply using the randomized assignment of monetary prizes in a large sample of Swedish lottery players. Winning a lottery prize modestly reduces earnings, with the reduction being immediate, persistent, and quite similar by age, education, and sex. A calibrated dynamic model implies lifetime marginal propensities to earn out of unearned income from -0.17 at age 20 to -0.04 at age 60, and labor supply elasticities in the lower range of previously reported estimates. The earnings response is stronger for winners than their spouses, which is inconsistent with unitary household labor supply models.
|
|
| 10. |
- Cesarini, David, et al.
(författare)
-
The effect of wealth on household labor supply : evidence from Swedish lotteries
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We study the effect of wealth on labor supply using the randomized assignment of monetary prizes in a large sample of Swedish lottery players. We find winning a lottery prize modestly reduces labor earnings, with the reduction being immediate, persistent, and similar by age, education, and sex. A calibrated dynamic model of individual labor supply implies an average lifetime marginal propensity to earn out of unearned income of -0.11, and labor-supply elasticities in the lower range of previously reported estimates. The earnings response is stronger for winners than their spouses, which is inconsistent with unitary household labor supply models.
|
|
| 11. |
- Cesarini, David, et al.
(författare)
-
The Effect of Wealth on Individual and Household Labor Supply : Evidence from Swedish Lotteries
- 2017
-
Ingår i: The American Economic Review. - : American Economic Association. - 0002-8282 .- 1944-7981. ; 107:12, s. 3917-3946
-
Tidskriftsartikel (refereegranskat)abstract
- We study the effect of wealth on labor supply using the randomized assignment of monetary prizes in a large sample of Swedish lottery players. Winning a lottery prize modestly reduces earnings, with the reduction being immediate, persistent, and quite similar by age, education, and sex. A calibrated dynamic model implies lifetime marginal propensities to earn out of unearned income from -0.17 at age 20 to -0.04 at age 60, and labor supply elasticities in the lower range of previously reported estimates. The earnings response is stronger for winners than their spouses, which is inconsistent with unitary household labor supply models.
|
|
| 12. |
- Cesarini, David, et al.
(författare)
-
The Effect of Wealth on Individual and Household Labor Supply : Evidence from Swedish Lotteries
- 2015
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We study the effect of wealth on labor supply using the randomized assignment of monetary prizes in a large sample of Swedish lottery players. We find winning a lottery prize modestly reduces labor earnings, with the reduction being immediate, persistent, and similar by age, education, and sex. A calibrated dynamic model of individual labor supply implies an average lifetime marginal propensity to earn out of unearned income of -0.11, and labor-supply elasticities in the lower range of previously reported estimates. The earnings response is stronger for winners than their spouses, which is inconsistent with unitary household labor supply models.
|
|
| 13. |
- Cesarini, David, et al.
(författare)
-
Wealth, Health, and Child Development : Evidence from Administrative Data on Swedish Lottery Players
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We use administrative data on Swedish lottery players to estimate the causal impact of substantial wealth shocks on players' own health and their children's health and developmental outcomes. Our estimation sample is large, virtually free of attrition, and allows us to control for the factors conditional on which the prizes were randomly assigned. In adults, we find no evidence that wealth impacts mortality or health care utilization, with the possible exception of a small reduction in the consumption of mental health drugs. Our estimates allow us to rule out effects on 10-year mortality one sixth as large as the cross-sectional wealth-mortality gradient. In our intergenerational analyses, we find that wealth increases children's health care utilization in the years following the lottery and may also reduce obesity risk. The effects on most other child outcomes, which include drug consumption, scholastic performance, and skills, can usually be bounded to a tight interval around zero. Overall, our findings suggest that in affluent countries with extensive social safety nets, causal effects of wealth are not a major source of the wealth-mortality gradients, nor of the observed relationships between child-developmental outcomes and household income.
|
|
| 14. |
- Cesarini, David, et al.
(författare)
-
WEALTH, HEALTH, AND CHILD DEVELOPMENT : EVIDENCE FROM ADMINISTRATIVE DATA ON SWEDISH LOTTERY PLAYERS
- 2016
-
Ingår i: Quarterly Journal of Economics. - : Oxford University Press (OUP). - 0033-5533 .- 1531-4650. ; 131:2, s. 687-738
-
Tidskriftsartikel (refereegranskat)abstract
- We use administrative data on Swedish lottery players to estimate the causal impact of substantial wealth shocks on players' own health and their children's health and developmental outcomes. Our estimation sample is large, virtually free of attrition, and allows us to control for the factors conditional on which the prizes were randomly assigned. In adults, we find no evidence that wealth impacts mortality or health care utilization, with the possible exception of a small reduction in the consumption of mental health drugs. Our estimates allow us to rule out effects on 10-year mortality one sixth as large as the cross-sectional wealth-mortality gradient. In our intergenerational analyses, we find that wealth increases children's health care utilization in the years following the lottery and may also reduce obesity risk. The effects on most other child outcomes, including drug consumption, scholastic performance, and skills, can usually be bounded to a tight interval around zero. Overall, our findings suggest that in affluent countries with extensive social safety nets, causal effects of wealth are not a major source of the wealth-mortality gradients, nor of the observed relationships between child developmental outcomes and household income.
|
|
| 15. |
- Claesson, Åsa, et al.
(författare)
-
lntegrated Optical Fiber Sensors in Additive Manufactured Metal Components for Smart Manufacturing Applications
- 2019
-
Ingår i: Smart Systems Integration; 13th International Conference and Exhibition on Integration Issues of Miniaturized Systems.
-
Konferensbidrag (refereegranskat)abstract
- This work combines fiber optic sensors with additive manufacturing to enable integration of temperature and strain sensors in metal components. In this paper, we present a fiber optic sensor network integrated in press hardening tools to monitor the contact between the tool and the metal sheet during forming operation. The tools are manufactured through metal powder bed fusion using laser melting processes (PBF-SLM), after which the tools are prepared for sensor integration. A demonstrator press hardening tool with integrated fiber optic sensors was heated using an electric heat foil and the sensor measurements was compared to a thermal simulation model. The sensor technology is based on Fiber Bragg Gratings (FBGs), integrated at several positions along the optical fiber. FBGs are in-fiber sensors that are multiplexed. lt is possible to place hundreds of FBG sensors along one single fiber, thus allowing for quasidistributed sensing of temperature or strain. The optical fiber itself can be less than 100 micrometer in diameter, allowing for sensing at several points in a minimally invasive way, when integrated in a tool or component.
|
|
| 16. |
- Gingell, Imogen, et al.
(författare)
-
MMS Observations and Hybrid Simulations of Surface Ripples at a Marginally Quasi-Parallel Shock
- 2017
-
Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:11, s. 11003-11017
-
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.
|
|
| 17. |
- Goodrich, Katherine A., et al.
(författare)
-
MMS Multipoint electric field observations of small-scale magnetic holes
- 2016
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:12, s. 5953-5959
-
Tidskriftsartikel (refereegranskat)abstract
- Small-scale magnetic holes (MHs), local depletions in magnetic field strength, have been observed multiple times in the Earth's magnetosphere in the bursty bulk flow (BBF) braking region. This particular subset of MHs has observed scale sizes perpendicular to the background magnetic field (B) less than the ambient ion Larmor radius (rho(i)). Previous observations by Time History of Events and Macroscale Interactions during Substorms (THEMIS) indicate that this subset of MHs can be supported by a current driven by the E x B drift of electrons. Ions do not participate in the E x B drift due to the small-scale size of the electric field. While in the BBF braking region, during its commissioning phase, the Magnetospheric Multiscale (MMS) spacecraft observed a small-scale MH. The electric field observations taken during this event suggest the presence of electron currents perpendicular to the magnetic field. These observations also suggest that these currents can evolve to smaller spatial scales.
|
|
| 18. |
- Goodrich, Katherine A., et al.
(författare)
-
MMS Observations of Electrostatic Waves in an Oblique Shock Crossing
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:11, s. 9430-9442
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution particle and wave measurements taken during an oblique bow shock crossing by the Magnetospheric Multiscale (MMS) mission are analyzed. Two regions of differing magnetic behavior are identified within the shock, one with active magnetic fluctuations and one with laminar interplanetary magnetic field topology. A prominent reflected ion population is observed in both regions. The active magnetic region is characterized by large-amplitude (>100 mV/m) electrostatic solitary waves, electron Bernstein waves, and ion acoustic waves, along with intermittent current activity and localized electron heating. In the region of laminar magnetic field, ion acoustic waves are prominently observed. Solar wind ion deceleration is observed in both regions of active and laminar magnetic field. All observations suggest that solar wind deceleration can occur as a result of multiple independent processes, in this case current and ion-ion instabilities.
|
|
| 19. |
- Knechtel, Maricel L, 1968-
(författare)
-
Categorization Work in the Swedish Welfare State : Doctors and social insurance officers on persons with mental ill-health
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation contributes to the debate on street-level bureaucracy, which highlights how the decisions made by workers in public bureaucracies effectively become public policy. This debate has paid relatively little attention to the study of how professionals carry out their work by means of institutional categorization, a knowledge gap that this study helps to close. Moreover, this study contributes to the understanding of how persons with mental ill-health are matched with institutional categories.The aim of this dissertation is to shed light on the institutional categorization process involving persons with mental ill-health in two interrelated areas of welfare settings: primary healthcare and sickness insurance. To pursue this aim, 27 in-depth interviews with 30 participants (18 doctors and 12 social insurance officers) were performed. The interviews, which were based on vignettes – short hypothetical scenarios – made it possible to get insight into how doctors and social insurance officers would reason in a situation similar to that depicted in the vignette.This study emphasizes how discretion is exercised when individuals are matched with the institutional categories that doctors in primary health settings and social insurance officers have at their disposal. Ideally, this process is a rational process through which clients’ objective traits are assessed against the criteria that define the various institutional categories. However, the process is not straightforward; thus, different kinds of social mechanisms are linked to the processes of institutional categorization, such as signaling, screening, the logic of appropriateness, moral work, and discrimination. On a more practical level, this study emphasizes the difficulties imbued in the process of institutional categorization. There are multiple reasons for these difficulties. Human complexity is one of them: the interviewed professionals often work with situations that require responses to human dimensions, which are oftentimes too complicated to reduce to standard formats. Another reason for these difficulties has to do with the ambiguity and/or complexity of institutional category schemes. Moreover, the process of institutional categorization takes place in a context of conflicting demands and professional logics, both within a single organization and across the organizations that work together with respect to the same patient/client.Future research concerned with institutional categorization should address how persons with mental ill-health are matched with the institutional categories in other areas of welfare, such as social services and employment services. A deeper knowledge about how the various organizations of the welfare state match individuals with institutional categories, could bring us closer to an understanding of the problems of multi-organizational collaboration.
|
|
| 20. |
- Lindqvist, Erik, et al.
(författare)
-
Long-run Effects of Lottery Wealth on Psychological Well-being
- 2018
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We surveyed a large sample of Swedish lottery players about their psychological well-being and analyzed the data following pre-registered procedures. Relative to matched controls, large-prize winners experience sustained increases in overall life satisfaction that persist for over a decade and show no evidence of dissipating with time. The estimated treatment effects on happiness and mental health are significantly smaller, suggesting that wealth has greater long-run effects on evaluative measures of well-being than on affective ones. Follow-up analyses of domain-specific aspects of life satisfaction clearly implicate ?financial life satisfaction as an important mediator for the long-run increase in overall life satisfaction.
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
- Lu, Ru-Sen, et al.
(författare)
-
Detection of Intrinsic Source Structure at similar to 3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A*
- 2018
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 859:1
-
Tidskriftsartikel (refereegranskat)abstract
- We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A*, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional uv coverage in the N-S direction, and leads to a spatial resolution of similar to 30 mu as (similar to 3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of similar to 4%-13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of similar to 3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk-and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.
|
|
| 24. |
- Nakamura, Rumi, et al.
(författare)
-
Multiscale Currents Observed by MMS in the Flow Braking Region
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:2, s. 1260-1278
-
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.
|
|
| 25. |
- Nakamura, Rumi, et al.
(författare)
-
Near-Earth plasma sheet boundary dynamics during substorm dipolarization
- 2017
-
Ingår i: Earth Planets and Space. - : Springer Berlin/Heidelberg. - 1343-8832 .- 1880-5981. ; 69
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL similar to -1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 RE were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) Bz disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another fieldaligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet.
|
|
| 26. |
- Roquet, Fabien, et al.
(författare)
-
Stability of the thermohaline circulation examined with a one-dimensional fluid loop
- 2017
-
Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 69:1
-
Tidskriftsartikel (refereegranskat)abstract
- The Stommel box model elegantly demonstrates that the oceanic response to mixed boundary conditions, combining a temperature relaxation with a fixed salt flux forcing, is non-linear owing to the so-called salt advection feedback. This non-linearity produces a parameter range of bi-stability associated with hysteresis effects characterised by a fast thermally driven mode and a slow salinity-driven mode. Here, we investigate whether a similar dynamical behaviour can be found in the thermohaline loop model, a one-dimensional analogue of the box model. Asemi-analytical method to compute possible steady states of the loop model is presented, followed by a linear stability analysis carried out for a large range of loop configurations. While the salt advection feedback is found as in the box model, a major difference is obtained for the fast mode: an oscillatory instability is observed near the turning point of the fast mode branch, such that the range of bi-stability is systematically reduced, or even removed, in some cases. The oscillatory instability originates from a salinity anomaly that grows exponentially as it turns around the loop, a situation that may occur only when the salinity torque is directed against the loop flow. Factors such as mixing intensity, the relative strength of thermal and haline forcings, the non-linearity of the equation of state or the loop geometry can strongly affect the stability properties of the loop.
|
|
