Displays

Energy and circulation in the Earth’s magnetosphere and ionosphere are largely determined by conditions in the solar wind and interplanetary magnetic field. When the driving from the solar wind is turned off (to a minimum), we expect the activity to die down but exactly how this happens is not known.  Utilizing global MHD modelling, we have addressed the questions of what constitutes the quietest state for the magnetosphere and how it is approached following a northward turning in the IMF that minimizes the driving. We observed an exponential decay with a decay time of about 1 hr in several integrated parameters related to different aspects of magnetospheric activity, including the total field-aligned current into and out of the ionosphere.  The time rate of change for the cessation of activity was also measured in total field aligned current estimates from the AMPERE project, adding observational support to this finding.  Events of distinct northward turnings of the interplanetary magnetic field were identified, with prolonged periods of stable southward driving conditions followed by northward interplanetary magnetic field conditions. A well-defined exponential decay could be identified in the total hemispheric field-aligned current following the northward turning with a generic decay constant of 0.9, corresponding to an e-folding time of 1.1 hr. A possible physical explanation for the exponential decay follows from considering what needs to happen for the convection in the magnetosphere to slow down, or stop, namely the unwinding of the field-aligned current carrying flux tubes in the coupled magnetosphere-ionosphere system. A statistical analysis of the ensemble of events also reveals both a seasonal and a day/night variation in the decay parameter, with faster decay observed in the winter than in the summer hemisphere and on the nightside than on the dayside. These results can be understood in terms of stronger/weaker line tying of the ionospheric foot points of magnetospheric field lines for higher/lower conductivity.  Additional global modeling results with varying conductance scenarios for the ionosphere confirm this interpretation.   

How to cite: Moretto Jorgensen, T., Hesse, M., Rastaetter, L., Vennerstrom, S., and Tenfjord, P.: How does the magnetosphere go to sleep?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5502, https://doi.org/10.5194/egusphere-egu2020-5502, 2020.

We present the first hybrid-Vlasov simulations of proton precipitation in the polar cusps. We use two runs from the Vlasiator model to compare cusp proton precipitation fluxes during southward and northward interplanetary magnetic field (IMF) driving. The simulations reproduce well-known features of cusp precipitation, such as a reverse dispersion of precipitating proton energies, with proton energies increasing with increasing geomagnetic latitude under northward IMF driving, and a nonreversed dispersion under southward IMF driving. The cusp location is also found more poleward in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the precipitation takes place in the form of successive bursts during southward IMF driving, those bursts being associated with the transit of flux transfer events in the vicinity of the cusp. In the northward IMF simulation, dual lobe reconnection takes place. As a consequence, in addition to the high-latitude precipitation footprint associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere’s lobe reconnection site. The proton velocity distribution functions along the newly closed dayside magnetic field lines exhibit multiple proton beams travelling parallel and antiparallel to the magnetic field direction, which is consistent with observations with the Cluster spacecraft. We suggest that precipitating protons originating from the opposite hemisphere’s lobe reconnection site, albeit infrequent, could be observed in a situation of dual lobe reconnection.

How to cite: Grandin, M., Turc, L., Battarbee, M., Ganse, U., Johlander, A., Pfau-Kempf, Y., Dubart, M., and Palmroth, M.: Hybrid-Vlasov simulation of auroral proton precipitation in the cusps: Comparison of northward and southward interplanetary magnetic field driving, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3023, https://doi.org/10.5194/egusphere-egu2020-3023, 2020.

It is a relatively recent discovery that charge exchange soft X-ray emission is produced in the interaction of solar wind high charge ions with neutrals in the Earth’s exosphere; this has led to the realization that imaging this emission will provide us with a global and novel way to study solar-terrestrial interactions.

In particular X-ray imaging will provide us with the means of establishing the location of the magnetopause and the morphology of the magnetospheric cusps. Variations of the magnetopause standoff distance indicate global magnetospheric compressions and expansions, both in response to solar wind variations and internal magnetospheric processes.

Soft X-ray imaging is one of the main objectives of SMILE (Solar wind Magnetosphere Ionosphere Link Explorer), a joint space mission by ESA and the Chinese Academy of Sciences, which is under development and is due for launch in 2023. This presentation will introduce the scientific aims of SMILE, show simulations of the expected images to be returned by SMILE’s Soft X-ray Imager for different solar wind conditions, and will discuss some of the techniques that will be applied in order to extract the positions of the Earth’s magnetic boundaries, such as the magnetopause standoff distance.

How to cite: Branduardi-Raymont, G., Sembay, S., Sun, T., Connor, H., and Samsonov, A.: Imaging the Earth’s magnetic environment in soft X-rays with SMILE, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10877, https://doi.org/10.5194/egusphere-egu2020-10877, 2020.

Presently, all empirical coupling functions quantifying the solar wind - magnetosphere energy- or magnetic flux conversion, assume that the coupling is independent of the sign of the dawn-dusk component (By) of the Interplanetary Magnetic Field (IMF). In this paper we present observations strongly suggesting an explicit IMF By effect on the solar wind - magnetosphere coupling. When the Earth's dipole is tilted in the direction corresponding to northern winter, positive IMF By is found to on average lead to a larger polar cap than when IMF By is negative during otherwise similar conditions. This explicit IMF By effect is found to reverse when the Earth's dipole is inclined in the opposite direction (northern summer), and is consistently observed from both hemispheres using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to infer the size of the region 1/2 current system. Two interpretations are presented: 1) The dayside reconnection rate is affected by the combination of dipole tilt and IMF By sign in a manner explaining the observations 2) The combination of dipole tilt and IMF By sign affect the global conditions for maintaining a given nightside reconnection rate. The observations as well as idealized magnetohydrodynamic (MHD) model runs are analyzed and discussed in light of the two different interpretations in order to enhance our understanding of this explicit IMF By effect.

How to cite: Reistad, J. P., Ohma, A., Laundal, K. M., Moretto, T., Milan, S., and Østgaard, N.: On the origins of an explicit IMF By dependence on solar wind - magnetosphere coupling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19932, https://doi.org/10.5194/egusphere-egu2020-19932, 2020.

We study the role of substorms and steady magnetospheric convection (SMC) in magnetic flux transport in the magnetosphere, using observations of field-aligned currents (FACs) by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE).  We identify two classes of substorm, with onsets above and below 65^o magnetic latitude, which display different nightside FAC morphologies.  We show that the low-latitude onsets develop a poleward-expanding auroral bulge, and identify these as substorms that manifest ionospheric convection-braking in the auroral bulge region.  We show that the high-latitude substorms, which do not experience braking, can evolve into SMC events if the interplanetary magnetic field (IMF) remains southwards for a prolonged period following onset.  Our results provide a new explanation for the differing modes of response of the terrestrial system to solar wind-magnetosphere-ionosphere coupling, as understood in the context of the expanding/contracting polar cap paradigm, by invoking friction between the ionosphere and atmosphere.

How to cite: Milan, S., Carter, J., Walach, M.-T., Sangha, H., and Anderson, B.: Substorm onset latitude and the steadiness of magnetospheric convection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2591, https://doi.org/10.5194/egusphere-egu2020-2591, 2020.

The presence of heavy ions has a profound impact on the temporal response of the magnetosphere to internal and external forcing, and plays a key role in plasma entry and transport processes within the terrestrial magnetosphere.

Numerous studies focused on the transport and energization of O⁺ through the ionosphere-magnetosphere system; however, relatively few have considered the contribution of N⁺ to the near-Earth plasma, even though past observations have established that N⁺ is a significant ion species in the ionosphere and its presence in the magnetosphere is significant. In spite of only 12% mass difference, N⁺ and O⁺ have different ionization potentials, scale heights and charge exchange cross sections. The latter, together with the geocoronal density distribution, plays a significant role in the formation of ENAs, which in turn controls the energy budget of the inner magnetosphere, and the overall loss of the ring current. Therefore, the outflow of N⁺ from the ionosphere, in addition to that of O⁺, affects the global structure and properties of the current sheet, the mass loading of the magnetosphere, and it leads to changes in the local properties of the plasma, which in turn can influence waves propagation.

This study involves an integrated computational view of geospace, that solves and tracks the evolution of all relevant ion species, to systematically assess their regional and global influence on the various loss and acceleration mechanisms operating throughout the terrestrial magnetosphere. We employ the newly developed Seven Ion Polar Wind Outflow Model (7iPWOM), which in addition to tracking the transport of H⁺, He⁺ and O⁺, now solves for the heating and transport of N⁺, N₂⁺, NO⁺ and O₂⁺ in Earth’s polar wind. The 7iPWOM is coupled with a two-stream model of superthermal electrons (GLobal airglow, or GLOW) to account for the attenuated radiation, electron beam energy dissipation, and secondary electron impact. We show that during various solar conditions, the polar wind outflow solution using 7iPWOM improves significantly when compared with OGO observations.

In addition, numerical simulations using the kinetic drift Hot Electron Ions Drift Integrator (HEIDI) model suggest that the contribution of outflowing N⁺ to the ring current dynamics is significant, as the presence of N⁺alters the development and the decay rate of the ring current. Electron transfer collisions are far more efficient at removing N⁺ the system, compared with the removal of O⁺ ions. Synthetic TWINS-like mass separated ENA images show that the presence on nitrogen ions in the ring current, even in small amounts, significantly alters the ENA fluxes, and the peak of oxygen ENA fluxes can vary for up to an order of magnitude, depending on the magnetosphere composition. These findings can explain recent observations of faster than expected decay of high energy oxygen ions, as measured by the RBSPICE instrument on board of the Van Allen Probe spacecraft. We speculate that the abundance of oxygen has been mis-estimated, as it is likely that some of the oxygen measurements to actually be include comparable abundances of nitrogen ions.

How to cite: Ilie, R., Lin, M.-Y., Glocer, A., and Bashir, M. F.: Tracking the Differential Transport and Acceleration of Nitrogen and Oxygen Ions from the Terrestrial Ionosphere to the Inner Magnetosphere , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10158, https://doi.org/10.5194/egusphere-egu2020-10158, 2020.

In this work, the interactions between the solar wind and the magnetosphere of Saturn are studied via state-of-the-art global MHD simulations, focusing on the release of plasmoids in the magnetotail. We analyze in detail the occurrence rate, the size, the speed and the evolution of the plasmoids in the simulations and compare the results with in-situ measurements. In our simulations, the multi-species three-dimensional MHD equations are solved with the code MPI-AMRVAC on a spherical non-uniform mesh ranging from 3 Rs (inner boundary) to 200 Rs (outer boundary). In order to simulate the magnetosphere-ionosphere coupling, to accelerate the ionospheric plasma up to rigid corotation and to close the electrical current systems, ion-neutral collisions are introduced in the MHD equations in the ionospheric region near the inner boundary. The strong mass-loading associated with the moon Enceladus is also included as an axisymmetric torus centered at 5.5 Rs.

How to cite: Chané, E.: Plasmoid releases in the Saturn's magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8824, https://doi.org/10.5194/egusphere-egu2020-8824, 2020.

Magnetic reconnection permits topological rearrangements of the interplanetary and magnetospheric magnetic fields and the entry of solar wind mass, energy, and momentum into the magnetosphere. Thus, magnetic reconnection is a key issue to understand space weather. However, it hasnot been fully understood yet under which interplanetary/magnetosheath conditions magnetic reconnection takes place more effectively at the dayside magnetopause. For this purpose,  in the present study 25 dayside magnetopause reconnection events are investigated using the Time History of Events and Macroscale Interactions during Substorms ( THEMIS ) spacecraft  observations. It was found, (1) that the reconnection electric field is proportional to the interplanetary electric field, (2) that the reconnection electric field is inversely proportional to the solar wind-Alfvén Mach number,  (3) that thereconnection outflow speed is proportional to the solar wind Alfvén speed, and (4) that the reconnection outflow speed is  inversely proportional to the magnetosheath plasma beta. Finally, it is shown that the range of magnetic shear angles for which magnetic reconnection should occur is restricted to large shears as the magnetosheath flow direction becomes more perpendicular to the direction of the local magnetopause normal vector. Since these results refer to fairly typical solar wind-Alfvén Mach number condition, they may not apply to more extreme cases.

How to cite: Gonzalez, W. and Koga, D.: Dependence of magnetopause reconnection events on interplanetary parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5163, https://doi.org/10.5194/egusphere-egu2020-5163, 2020.

Plasma waves are ubiquitous in the Earth's magnetosheath. The most observed waves arise from instabilities generated by temperature anisotropy on the ions and electrons, such as the mirror and proton cyclotron instabilities. Along with observations, space physics is increasingly relying on the support of numerical simulations to understand these waves and instabilities. However, numerical simulations come with resolution limitations. We investigate here the spatial resolution dependence of the mirror and proton cyclotron instabilities in a global-hybrid Vlasov simulation with the use of the Vlasiator model. We compare the proton velocity distribution functions, power spectrum and growth rate of the instabilities in a simulation with three different spatial resolutions. We find that the proton cyclotron instability is absent at the lowest resolution and that the mirror instability is dominating, increasing the overall temperature anisotropy of the simulation. We also conducted a test at higher resolution and found out that this does not improve the description of the proton cyclotron instability significantly enough to justify this increase in resolution at the cost of numerical resources in future simulations. These results will be used for a future sub-grid model in order to mimic the energy dissipation processes at work at smaller scales without increasing the resolution of the simulation.

How to cite: Dubart, M., Ganse, U., Osmane, A., Battarbee, M., Grandin, M., Johlander, A., Pfau-Kempf, Y., Turc, L., and Palmroth, M.: Spatial resolution dependence of ion-scale waves in a global-hybrid Vlasov simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6780, https://doi.org/10.5194/egusphere-egu2020-6780, 2020.

 CLUSTER experimental observations of  Lavraud et al. (2005) have evidenced the presence of a particular layer (so –called herein Alfven Transition Layer or ATL) almost adjacent to the upper edge of the stagnant exterior cusp (SEC), through which the plasma flow transits from super-(from magnetosheath) to sub- (to SEC) Alfvenic regime as the interplanetary magnetic field (IMF) is northward. Three dimensional globa PIC simulations have been recently used  (Cai et al., 2015) to analyze the main features of the cusp for an IMF configuration similar that in the observations. These simulations have allowed us to complete the global view of the cusp region  (in particular the features not accessible by MHD approach).  A  detailed analysis has allowed to retrieve the features of the ATL which reveals to be associated to the complicated 3D particles entry into the cusp region and exhibit an internal conic depletion region (CDR) where the ion fluxes concentrate and are very strong (which suggests very local ion precipitation). Moreover, simulation results show that the ATL expands towards areas out and even far from the cusp region and outside the meridian plane.

                     In the present work, the study is extended for different Ma regimes of the solar wind, as the IMF stays in northward  configuration. Results show the impact of this Ma variation on the 3D features of the overall magnetosphere and in particular on the cusp region, i.e. (i) on the 3D ATL structures/spatial scales, (ii) on the extension of the region surrounded by the ATL, and (iii) on the structures, the spatial scales and the dynamics of the CDR itself.

How to cite: Cai, D. and Lembege, B.: Impact of the low/high Alfven Mach number regime of the solar wind on the Aflven transition Layer of the cusp for IMF North: 3D global PIC simulation., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3870, https://doi.org/10.5194/egusphere-egu2020-3870, 2020.

Geomagnetic storms generate a complex and highly time-dependent response in the magnetosphere-ionosphere system. Enhancement in field-aligned currents (FACs) can be very localised, and so accurately predicting the stormtime response of the ionosphere is crucial in forecasting the potential impacts of a severe space weather event at a given location on the Earth. Global MHD simulations provide a means to model ionospheric conditions in real-time for a given geomagnetic storm, allowing direct comparison to space- and ground-based observations from which the observations can be placed in global context to better understand the physical drivers behind the system's response.                   

Using the Gorgon MHD code and driving with upstream data from the ACE spacecraft, we simulate the state of the magnetosphere-ionosphere system during a geomagnetic storm commencing on 3^rd May 2014. To elucidate the characteristic timescales of the system response during this event, we adopt a novel approach originally applied by Shore et al. (2019) to ground magnetic field data from SuperMAG, and by Coxon et al. (2019) to FAC data from AMPERE. In this method the simulated FAC at each point on the ionospheric grid is cross-correlated with solar wind time-series for time lags of up to several hours, and the lag with the strongest correlation is identified.

From this we construct maps of the characteristic response timescale and strength of correlation in the ionosphere to IMF B_y and B_z, and interpret these results in terms of the varying stormtime FAC morphology by comparing the simulation results to observations by AMPERE and SuperMAG during this same event. Finally, we identify sources of asymmetry in the ionospheric response, such as that between day/night and north/south, relating these to asymmetries in magnetospheric dynamics such as magnetopause and magnetotail reconnection, and changes in global convection as the system reconfigures. This will reveal the importance of different aspects of magnetosphere-ionosphere system in influencing the coupling timescales, as well as the role of onset time in determining the potential impacts of a severe event.

References:

Shore, R. M., Freeman, M. P., Coxon, J. C., Thomas, E. G., Gjerloev, J. W., & Olsen, N. (2019). Spatial variation in the responses of the surface external and induced magnetic field to the solar wind. Journal of Geophysical Research: Space Physics, 124. https://doi.org/10.1029/2019JA026543

Coxon, J. C., Shore, R. M., Freeman, M. P., Fear, R. C., Browett, S. D., Smith, A. W., et al. (2019). Timescales of Birkeland currents driven by the IMF. Geophysical Research Letters, 46, 7893– 7901. https://doi.org/10.1029/2018GL081658

How to cite: Eggington, J., Coxon, J., Shore, R., Desai, R., Mejnertsen, L., Eastwood, J., and Chittenden, J.: Timescales of Ionospheric Field-Aligned Currents during a Geomagnetic Storm: Global Magnetospheric Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16461, https://doi.org/10.5194/egusphere-egu2020-16461, 2020.

The IMF B_y component is a source of numerous asymmetric features in our magnetospheric system, e.g. north-south asymmetries in the aurora, the magnetospheric and ionospheric current systems and the plasma convection. Several recent studies have shown that asymmetries in the lobe pressure play a major role in inducing these asymmetries. It has also been reported that enhanced tail reconnection affects the dynamics of the system by reducing the north-south asymmetries imposed by the IMF. A possible interpretation of these observations is that enhanced reconnection in the near-Earth tail reduces the pressure in the lobes and thus suppresses the cause of the initial asymmetry. In this study, we present the results from global MHD simulations using the LFM model to further investigate how enhanced tail reconnection affects the asymmetric state of the system. A relaxation of the asymmetry in the closed magnetosphere is seen in the model when the reconnection rate in the tail increases, consistent with observations, and we use the simulation output to gain further insight into the physical mechanism(s) responsible for the return to a more symmetric state.

How to cite: Ohma, A., Østgaard, N., Reistad, J. P., Laundal, K. M., and Tenfjord, P.: How tail reconnection affects the asymmetric state of the magnetosphere in the LFM model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20250, https://doi.org/10.5194/egusphere-egu2020-20250, 2020.

The magnetospheric substorm is a response mode of the magnetosphere to solar wind driving. It has been shown that substorms can show repetitive behavior (that is, three or more substorms following each other with a quasi-period). The most common period is approximately three hours. A conclusive and satisfactory answer to the cause of this periodicity has not yet been given. Very limited mentioning of a shorter recurrence period, namely around one hour, has sparsely been appeared in the literature. In this presentation, we report on this lesser studied periodicity, giving observational examples from the THEMIS fleet. We compare the observations with global magnetosphere MHD simulations (BATS-R-US) of solar wind-magnetosphere coupling that incorporate kinetic corrections at the reconnection site. The similarity is striking, suggesting that indeed kinetic effects in tail reconnection are responsible - at least in some cases - for this periodic behavior of the magnetosphere.

How to cite: Keiling, A., Nosé, M., and Angelopoulos, V.: Solar wind-magnetosphere coupling in the form of recurrent substorms with one-hour periodicity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22329, https://doi.org/10.5194/egusphere-egu2020-22329, 2020.

Understanding the transport of hot plasma from tail towards the inner magnetosphere is of great importance to improve our perception of the near-Earth space environment. In accordance with the recent observations, the contribution of bursty bulk flows (BBFs)/bubbles in the inner plasma sheet especially in the storm-time ring current formation is nonnegligible. These high-speed plasma flows with depleted flux tube/entropy are likely formed in the mid tail due to magnetic reconnection and injected earthward as a result of interchange instability. In this presentation, we investigate the interplay of these meso-scale structures on the average magnetic field and plasma distribution in various regions of the plasma sheet, using the Inertialized Rice Convection Model (RCM-I). We will discuss the comparison of our simulation results with the observational statistics and data-based empirical models.

How to cite: Sadeghzadeh, S. and Yang, J.: Interplay of bubble injections in the plasma sheet dynamics as inferred from RCM-I simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2120, https://doi.org/10.5194/egusphere-egu2020-2120, 2020.

In contrast to the simple conventional plasma flow convection governed by the Dungey Cycle, past studies have revealed that the plasma flows in the magnetotail region are more complicated, hosting high-speed bursty and meandering vortical flows. We have utilized magnetic field and plasma data from the Cluster mission to investigate a high speed earthward propagating flow burst with a peak velocity of ~530 km/s in the magnetotail plasma sheet (X_GSM ~ -17R_E) on 20 September 2002. In the vicinity of this flow burst, a vortical flow, whose plasma vectors are first directed tailward then earthward, is also observed. The plasma data shows that the plasma population in the vortical flow is likely to originate from the associated flow burst. In addition, the boundaries of both structures are also found to be tangential discontinuities, clearly surrounded by the ambient slow moving plasma sheet. Inside the vortical flow, there exists a region where plasma originating from the flow burst and ambient plasma sheet are mixed. The local segment of inbound boundary crossing of the vortical flow is shown to have a thickness that is non-uniform. Coupled with the flow evolution in the vortical flow, these characteristics are consistent to a boundary crossing of a vortical flow. The magnetic field on the flow burst is quasi-perpendicular to the large velocity shear (~460 km/s) across the flow burst boundary. These results suggest that the formation of vortical flow can arise from the development and subsequent growth of flow burst boundary wave as a result of Kelvin-Helmholtz instability. In summary, this article presents a detailed observational study of a vortical flow and the formation of which would serve as the first direct observational consequence of an excited and growing flow burst boundary wave. Continuous scattering of the detached vortices may play an important role in the braking mechanism of earthward propagating flow bursts. 

How to cite: Chong, G. S., De Spiegeleer, A., Hamrin, M., Pitkanen, T., Aizawa, S., Juusola, L., and Andersson, L.: Vortical flow in the plasma sheet: Non-linear growth of flow burst surface wave?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3312, https://doi.org/10.5194/egusphere-egu2020-3312, 2020.

Field-aligned currents (FACs), also known as Birkeland currents, are the agents by which momentum and energy can be transferred to the ionosphere from solar wind and the magnetosphere, exhibiting a seasonal variation as that of ionospheric conductance at low altitude. By using magnetic field and plasma measurements from the Magntospheric Multiscale (MMS), we estimated the properties of the small-scale FACs in the plasma sheet boundary layer (PSBL) region. The occurrence rates of those FACs are larger near the midnight plane and near the flank region; they are also larger in the northern (summer) hemisphere than in the southern hemisphere, especially for the earthward FACs. Different distribution patterns as a function of plasma β are found for the Beam-type FACs and the Flow-type FACs (accompanied with observable perpendicular currents). The latter are closer to central plasma sheet (higher β) and their occurrence rate decreases linearly toward tail lobe (lower β), while the former mainly appear within the β range of 0.1 to 1. FAC magnitudes show little dependence on plasma β, while they would increase when approaching Earth generally. The occurrence rate and magnitude of FACs both increase from low to high geomagnetic activity, consistent with observation at ionospheric altitude. The main carriers for FACs in PSBL are thermal electrons, while cold electrons sometimes could also have contribution, especially under high geomagnetic activity. This study shows that FACs in the PSBL exhibit an asymmetry of occurrence rate between the northern and southern hemisphere and different signatures under low and high geomagnetic activity, which are consistent with FACs at ionospheric altitude. This demonstrates that FACs are significant in magnetosphere-ionosphere coupling and illustrates the possible ionospheric feedback effects to magnetosphere in the nightside.

How to cite: Chen, Y., Wu, M., Wang, G., Pan, Z., and Zhang, T.: Statistical Properties of Field-Aligned Currents in the Plasma Sheet Boundary Layer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4006, https://doi.org/10.5194/egusphere-egu2020-4006, 2020.

Recent statistical studies based on CLUSTER, CRRES, and THEMIS satellite data have provided insight into global plasmapause characteristics: start of erosion between 21-07 MLT and eastward azimuthal propagation. The observed plasmapause behavior is found to agree with the theory of the interchange instability mechanism. We present the results of the plasmapause characteristics obtained with simulations based on this mechanism.

Here we aim to obtain the same plasmapause characteristics that we previously obtained with simulations using real values of geomagnetic Kp index (which are the proxies for the convection electric field), but using synthetic Kp changes. We show that for that, completely unexpected, instead of many combinations of Kp changes occurring at different UT times (generated for instance with Monte Carlo methods), only 3 Kp jumps occurring at one UT time, leads to the same plasmapause characteristics obtained with simulations using the real Kp values. Therefore, two plasmapause datasets are constructed by setting the following input in the simulations: (a) real values of the geomagnetic Kp index, (b) certain types of time-dependent changes in the Kp (Kp jumps). The Kp jumps include sharp Kp increase, sharp Kp decrease, short time burst enhancement (increase-decrease within 3 hours) in Kp and their combinations in order to obtain plumes, shoulders, and notches, the structures most often observed in nature. The modeled plasmapause is cross-correlated with the Kp index at different 1-hour MLT bins.

We have shown that the cross-correlation curves provide deep insight into the physical processes related to the plasmapause dynamic and evolution. In single events, plasmapause may undergo complex and different dynamics. Here, we show that global plasmapause motions and deformation in time may be simply explained, at least in the statistical sense. Accordingly, we will demonstrate and discuss that three plasmapause structures and their combinations statistically leave the same imprint in the passage through a specific MLT sector as a combination of the plasmapauses created with a large number of the real Kp changes.  

How to cite: Verbanac, G., Bandic, M., and Pierrard, V.: Explanation of global plasmapause characteristics in the frame of interchange instability mechanism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10882, https://doi.org/10.5194/egusphere-egu2020-10882, 2020.

The coupling between the Earth’s magnetic field and the interplanetary magnetic field (IMF) transported by the solar wind results in a cycle of magnetic field lines opening and closing generally known as the Dungey substorm cycle, mostly governed by the process of magnetic reconnection. The geomagnetic field lines can therefore have either a closed or an open topology, i.e. lower latitude field lines are closed (map from southern ionosphere to the northern), while higher latitude field lines are open (map from one polar ionosphere into interplanetary space). Closed field lines can trap electrically charged particles that bounce between mirror points located in the North and South hemispheres while drifting in longitude around the Earth, forming the plasmasphere, the radiation belts and the ring current. The outer boundary of the plasmasphere is the plasmapause. Its location is mostly driven by the interplay of the corotation electric field of ionospheric origin, and the convection electric field that results from the interaction between the IMF and the geomagnetic field. At times of prolonged intense coupling between these fields, the response of the magnetosphere becomes global and a geomagnetic storm develops. The ring current created by the motion of the trapped energetic particles intensifies and then decays as the storm abates. This study aims to find a possible relationship between the evolution of the trapped population and the process of magnetic reconnection during storm times. The EUV instrument on board the NASA-IMAGE spacecraft observed the distribution of the trapped helium ions (He+) in the plasmasphere. We consider several cases of intense geomagnetic storms observed by the IMAGE satellite. We identify the plasmapause location (Lpp) during those cases. We find a strong correlation between the Dst index and Lpp. The ring current and the trapped particles are expected to vary during storms. We use the Tsyganenko magnetic field model to map the electric potential between the Heppner-Maynard boundary (HMB) in the ionosphere and the magnetosphere and estimate the voltage and electric field in the vicinity of the plasmapause. The ionospheric electric field is deduced from the ionospheric convection velocity measured by the SuperDARN (SD) radar network at high latitudes. The tangential electric field component of the moving plasmapause boundary is estimated from IMAGE-EUV observations of the plasmasphere and is compared with expectations based on the SD data. We combine measurements of the trapped population from IMAGE-EUV and IMAGE-FUV observations of the aurora to better understand and quantify the variability of the Earth's outer radiation belt during strong storms. The auroral precipitation at ionospheric latitude is studied using FUV imaging and compared to the He+ response during the storms.

How to cite: Matar, J., Hubert, B., Cowley, S., Milan, S., Yao, Z., Guo, R., Goldstein, J., and Sandel, B.: The Plasmasphere During Major Geomagnetic Storms: Analysis Of Trapped Particles In The Outer Radiation Belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-265, https://doi.org/10.5194/egusphere-egu2020-265, 2020.

The geomagnetic activity can modulate the number and energy fluxes of precipitation and their spatial distributions. Most previous studies examined precipitation in terms of energy spectrum types associated with quasi-static potential structures (QSPS) acceleration, Alfvénic acceleration, and wave scattering under various geomagnetic conditions. In this study, we instead categorize precipitation according to energy channels of particles. The spatial distribution of the precipitation for various energy channels is also derived under different geomagnetic conditions. Our results indicate that regardless of active and quiet times, low-energy (high-energy) precipitation is mostly distributed on the dayside (nightside). By comparing with past results, we infer that electron precipitation is mainly caused by QSPS and Alfvénic acceleration for most cases; however, the high-energy electrons during quiet times are predominantly created by wave scattering. For high-energy precipitation, the dawn-dusk asymmetry of the spatial distribution during active times is found to be opposite of that during quiet times. Based on their spatial distributions, we suggest that the high-energy precipitation during quiet times is dominated by the curvature and gradient drifts, while that during active times is mainly affected by physical processes related to substorms in the magnetotail.

How to cite: Shen, H.-W., Shue, J.-H., Dombeck, J., and Li, H.-M.: Spatial Distribution of Particle Precipitation in Terms of Energy Channels under Different Geomagnetic Conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2126, https://doi.org/10.5194/egusphere-egu2020-2126, 2020.

During geomagnetically disturbed times, geomagnetically induced currents (GICs) flow in power systems potentially causing damage to the system. The largest GICs are often produced when the surface geomagnetic field abruptly changes (for example, an induced rate of change of the horizontal magnetic field component, dH/dt). It is well established that intense dB/dt variations take place in the main phase of a geomagnetic storm, particularly while magnetic substorms occur during the active period. However, there are currently few studies that report intense dB/dt variations which are directly driven by bursty bulk flows (BBFs) at geosynchronous orbit. In this study, we investigate the characteristics and response in the magnetosphere-ionosphere system during the recovery phase of a geomagnetic storm that occurred on 7 January 2015 by using a multi-point approach combining space-borne Cluster and SWARM measurements, and a group of ground-based magnetometer observations. The locations of Cluster and SWARM map to the same conjugate region as the magnetometer ground stations at the time of the BBF. The measurements show that corresponding signals in all measurements occur simultaneously in this region. Our results suggest that the most intense dB/dt (dH/dt) variations are associated with R1-type FACs that are driven by BBFs at geosynchronous orbit around substorm onset.

How to cite: Wei, D., Dunlop, M., Yang, J., Yu, Y., and Wang, T.: Intense dB/dt variations driven by near-Earth Bursty Bulk Flows (BBFs): A case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7689, https://doi.org/10.5194/egusphere-egu2020-7689, 2020.

A method for determining the coordinates of geomagnetic perturbation sources based on joint data processing of the world network of magnetic observatories is proposed. A large statistical material showed the relationship of large geomagnetic storms with the interaction of two or more magnetic clouds formed as a result of coronal mass ejections. To determine the coordinates of the sources of perturbations, it is proposed to use the data of magnetic observatories of the "INTERMAGNET" international network, which has more than 100 observation points distributed around the world and equipped with modern identical hardware. The results of geomagnetic field measurement obtained by magnetic observatories are brought to a single coordinate system. It was achieved by rotation of the axes of local stations, which allows determining the coordinates of the sources of perturbations and evaluating the accuracy of specifying the coordinate system of each local observatory.

How to cite: Zhumabayev, B., Vassilyev, I., Protsenko, V., and Zhumabayeva, S.: About determination of coordinates of sources of geomagnetic perturbations according to the world network of magnetic observatories, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9947, https://doi.org/10.5194/egusphere-egu2020-9947, 2020.

The waiting time distributions and associated statistical relationships can be considered as a general strategy for analyzing space weather and inner magnetospheric processes to a large extent. It measures the distribution of delay times between subsequent hopping events in such processes. In a physical system the time duration between two events is called a waiting-time, like the time between avalanches. The burst lifetime can be considered as the time duration when magnitude of fluctuations are above a given threshold intensity.  If a characteristic time scale is absent then the probability densities vary with power-law relations having a scaling exponent. The burst lifetime distribution of the substorm index called as the Wp index (Wave and planetary), which reflects Pi2 wave power at low-latitude is considered for the present analysis. Our analysis shows that the lifetime probability distributions of Wp index yield power-law exponents. Even though power-law exponents are observed in magnetospheric proxies for different solar activity periods, not many studies were made to analyze whether these features will repeat or differ depending on sunspot cycle. We compare the variations of power-law exponents of Wp index and other magnetospheric proxies, such as AE index, during solar maxima and solar minima. Thus the study classifies the activity bursts in Wp and other magnetospheric proxies that may have different dynamical critical scaling features. We also expect that the study sheds light into certain stochastic aspects of scaling properties of the magnetosphere which are not developed as global phenomena, but in turn generated due to inherent localized properties of the magnetosphere.

How to cite: Prasad, P., Kumar G, S., and Gopinath, S.: Investigations on the power-law burst lifetime distribution characteristics of the magnetospheric system , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20011, https://doi.org/10.5194/egusphere-egu2020-20011, 2020.

The Earth's magnetosheath is luminous in the soft X-ray band, due to the solar wind charge exchange (SWCX) process. SWCX occurs when a heavy solar wind ion with a high charge state encounters with a neutral component. The heavy ion obtains an electron and gets into an excited state. It then decays to the ground state and emits a photon in the soft X-ray band. Considering that the X-ray emission from the magnetosheath is higher compared to that from the magnetosphere, information about the boundary positions can be derived from an X-ray image of the magnetosheath.

The solar wind - magnetosphere - ionosphere link explorer (SMILE) is a mission jointly supported by ESA and CAS, which aims at exploring the dynamics in the whole system. Soft X-ray Imager (SXI) is expected to provide X-ray images of the magnetosphere. The Modeling Working Group (MWG) is one of the four working groups of SMILE. Studies about the modeling of X-ray emissions as well as the method to derive the boundary positions are two main topics of the MWG. The main progress of MWG will be summarized here. 

How to cite: Sun, T.: Modeling the X-ray emissions from the geo-space environment , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21675, https://doi.org/10.5194/egusphere-egu2020-21675, 2020.