ST2.7

Comparison of observed magnetopause locations with model predictions can serve as a proof of our understanding of the interaction between solar wind and Earth magnetic field. Since the corresponding upstream conditions are usually derived from observation at L1, our knowledge on solar wind propagation and evolution on short scales are tested as well. We have collected about 40 000 of magnetopause crossings observed by THEMIS spacecraft in course of 2007–2019 years and compared the observed magnetopause position with prediction of several empirical magnetopause models using OMNI upstream parameters (mostly derived from ACE observations) and Wind magnetic field and plasma measurements propagated by our two-step propagation routine. The difference between observed and predicted magnetopause radial distance, Robs – Rmod was used for quantification of the model-observation agreement. We have found that the distribution of Robs – Rmod can be well fitted by the Gaussian distribution with FWHM ≈1.2 Re for all models and both upstream monitors. Nevertheless, the tails of the distributions are enhanced for all models and Robs – Rmod larger than 2 Re are rather frequent. A detailed analysis of such events leads to suggestions for improvement of investigated models or for a building of a new empirical model of the equatorial magnetopause.

How to cite: Nemecek, Z., Safrankova, J., Grygorov, K., Pi, G., Aghabozorgi Nafchi, M., Nemec, F., and Simunek, J.: Extreme magnetopause locations and their sources, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1359, https://doi.org/10.5194/egusphere-egu22-1359, 2022.

The magnetopause would be located at a point where the total pressure on the solar wind/magnetosheath side is equal to its magnetospheric counterpart. The upstream pressure is a sum of plasma thermal pressure and magnetic pressure whereas the magnetic pressure would strongly dominate on the magnetospheric side because the density of magnetospheric plasma is typically very low. Statistics of over ten years of THEMIS subsolar magnetopause (Y_GSM<5 R_E) observations reveals that about 2 % of magnetopause crossings exhibit notably higher magnetic field in the magnetosheath than within the magnetosphere and thus the pressure balance is apparently violated. On the other hand, long series of multiple crossings suggest that the magnetopause is close to its equilibrium position and upstream and downstream pressures should be about equal. Interestingly, such crossings were found under both polarities of IMF B_Z. In the paper, we study possible sources and mechanisms keeping the pressure balance. We discuss namely the upstream solar wind conditions and state of the outer magnetosphere. Comparison of these unusual magnetopause crossings with the rest of them shows that the cold plasma population coming to the magnetopause from the plasmasphere during periods of geomagnetic storms plays an important role in setting the pressure balance in the magnetopause region.

How to cite: Grygorov, K., Nemecek, Z., Safrankova, J., and Simunek, J.: Pressure balance at the subsolar magnetopause: Statistical study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1733, https://doi.org/10.5194/egusphere-egu22-1733, 2022.

Fluxes in the outer radiation belt can vary by orders of magnitude in response to solar wind driving conditions. Magnetopause shadowing, where electron and proton drift paths intersect the magnetopause boundary, is a fundamental loss process which operates on sub-day timescales and can result in rapid loss across the outer radiation belt. Accurate characterisation of this is therefore required to fully account for outer radiation belt dynamics and to avoid unrealistic fluxes impacting long-term forecasts. In this paper we utilise particle simulations of the radiation belts integrated within evolving global MHD simulations, to provide high-resolution high-fidelity simulations of the phenomenon of magnetopause shadowing. We model a variety of magnetopause compression scenarios corresponding to extreme cases of interplanetary shock impacts, and gradual increases in solar wind dynamic pressure. We thus constrain how time-dependent topological variation of the magnetospheric fields results in a complex interplay of open and closed particle drift paths, and examine the role of the electric field in modulating escaping particles trajectories as well as corresponding prompt injections into the inner magnetosphere.

How to cite: Desai, R., Eastwood, J., Eggington, J., Chittenden, J., and Horne, R.: Magnetospheric compressions, magnetopause shadowing and the last-closed-drift-shell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1765, https://doi.org/10.5194/egusphere-egu22-1765, 2022.

The mass and energy transfer across Earth’s magnetopause is caused by a variety of different plasma processes. One of these processes is the Kelvin-Helmholtz instability (KHI), excited by the velocity shear between the fast-flowing magnetosheath plasma and the relatively stagnant magnetosphere. It has been frequently observed during periods of northward interplanetary magnetic field (IMF), however much less is known about its behaviour during southward IMF conditions.

We present the first Magnetospheric Multiscale (MMS) observations of KH waves and vortices at the dusk-flank magnetopause during southward IMF conditions on September 23, 2017. The instability criterion for the KHI was fulfilled during this event. The boundary normal vectors, obtained by using multi-point methods, are consistent with the predicted structures of the KH waves. We further performed a series of realistic 2D and 3D fully kinetic PIC simulations based on the plasma parameters observed during this MMS event. A comparison to results from these simulations demonstrated quantitative consistencies with the MMS data in many aspects such as the flow and total pressure variations in the KH waves, and the signatures of the non-linearly rolled up KH vortices including the Low Density Faster Than Sheath (LDFTS) plasma.

The simulations further showed that secondary instabilities are excited at the edges of the primary KHI. The Rayleigh-Taylor instability (RTI) can lead to the penetration of high-density arms into the magnetospheric side and disturb the structures of the vortex layer, leading to irregular variations of the surface waves. This can be an important factor in explaining the lower observational probability of KH waves during southward IMF than northward IMF. In the non-linear growth stage of the primary KHI, the lower-hybrid drift instability (LHDI) is excited at the vortex edges leading to efficient plasma mixing across the magnetopause.

The high-time resolution of MMS measurements demonstrated the occurrence of kinetic-scale plasma waves mainly on the low-density side of the edges of the KH waves. Given quantitative consistencies with the simulations, these waves can be interpreted as being generated by the LHDI. These observed waves form due to the strong density gradient between the two sides of the boundary layer and can lead to a flattening of the edge layers.

In this presentation, we will show the consistencies between MMS observations and 2D and 3D simulation runs focusing on the large-scale surface waves (KHI, RTI) and the small-scale fluctuations (LHDI) and outline the multi-scale properties of the observed KH waves during southward IMF.

How to cite: Blasl, K. A., Nakamura, T., Plaschke, F., Nakamura, R., Hasegawa, H., Stawarz, J. E., Liu, Y.-H., Peery, S. A., Holmes, J. C., Hosner, M., Schmid, D., Roberts, O. W., and Volwerk, M.: Multi-scale observations and evolution of the magnetopause Kelvin-Helmholtz waves during southward IMF, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3465, https://doi.org/10.5194/egusphere-egu22-3465, 2022.

Ultra-low frequency (ULF) waves in the Pc5 range, with periods between 150 – 600 s, play a key role in the dynamics of Earth’s magnetosphere, in particular through their interaction with radiation belt electrons. One important source of magnetospheric Pc5 waves are fluctuations of the upstream solar wind parameters in the same frequency range. Pressure variations in the solar wind are thought to result in a forced breathing of the magnetosphere, as the magnetosphere would expand and compress in response to the changing upstream conditions, which drives ULF waves inside the magnetosphere. The details of the interaction of these solar wind variations with the Earth’s bow shock and magnetosheath, their impact on the magnetosheath plasma properties and how the fluctuations would change before reaching the magnetopause, remain however unclear. In this study, we investigate the influence of externally-driven variations across near-Earth space using global 2D simulations performed with the hybrid-Vlasov model Vlasiator. The new time-varying boundary setup in Vlasiator allows us to set Pc5 periodic density pulses coming from the upstream. The density pulses cause the breathing motion of the bow shock, create clear stripes of variations inside the magnetosheath, and modulate the electromagnetic ion cyclotron (EMIC) and mirror modes. We characterize the spatial-temporal variations of waves on the simulation plane within the magnetosheath and discuss the potential impact on the near-Earth environment.

How to cite: Zhou, H., Turc, L., Tarvus, V., Pfau-Kempf, Y., Battarbee, M., Dubart, M., Ganse, U., Alho, M., Grandin, M., George, H., Suni, J., Bussov, M., Papadakis, K., Manglayev, T., Horaites, K., Zaitsev, I., Cozzani, G., and Palmroth, M.: Magnetospheric Responses to Solar Wind Pc5 Density Fluctuations: Results from 2D Hybrid Vlasov Simulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5653, https://doi.org/10.5194/egusphere-egu22-5653, 2022.

We quantify the contributions of different convection states to the magnetic flux through-put of the magnetosphere during 2010. To do this we provide a continuous classification of convection state for the duration of 2010 based upon observations of the solar wind and interplanetary magnetic field, geomagnetic indices, and field-aligned currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Convection states are defined as 1) quiet and 2) weak activity, substorm 3) growth, 4) expansion, and 5) recovery phases, 6) substorm driven phase (when relatively steady magnetospheric convection occurs), 7) recovery bays (when recovery phase is accompanied by a negative excursion of the AL electrojet index), and 8) periods of multiple intensifications (storm-time periods when continuous short-period AL activity occur). The magnetosphere is quiet for 46% of the time, when very little convection takes place. The majority of convection occurs during growth and driven phases (21% and 38%, respectively, of open magnetic flux accumulation by dayside reconnection). We discuss these results in the context of the expanding/contracting polar cap model of convection, and describe a framework within which isolated substorms and disturbances during periods of more continuous solar wind-magnetosphere driving can be understood.

How to cite: Milan, S., Carter, J., Sangha, H., Bower, G., and Anderson, B.: Magnetospheric flux throughput in the Dungey cycle: identification of convection state during 2010, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2939, https://doi.org/10.5194/egusphere-egu22-2939, 2022.

It is well known that the polar cap, delineated by the Open
Closed field line Bound ary (OCB), responds to changes in the
Interplanetary Magnetic Field (IMF). In general, the boundary
moves equatorward when the IMF turns southward and contracts
poleward when the IMF turns northward. However, observations of
the OCB are spotty and limited in local time, making more
detailed studies of its IMF dependence difficult. Here, we
simulate five solar storm periods with the coupled
OpenGGCM-RCM-CTIM model to estimate the location and dynamics of
the OCB. For these events, polar cap boundary location
observations are also obtained from Defense-Meteorological
Satellite Pro- gram (DMSP) precipitation spectrograms and
compared with the model output. There is a large scatter in the
DMSP observations and in the model output. However, we generally
find good agreement between the model and the observations. On
average, the model overestimates the latitude of the open-closed
field line boundary by 1.61◦. Additional analysis of the
simulated polar cap boundary dynamics across all local times
shows that the MLT of the largest polar cap expansion closely
correlates with the IMF clock angle; that the strongest
correlation occurs when the IMF is southward; that during strong
southward IMF the polar cap shifts sunward; and that the polar
cap rapidly contracts at all local times when the IMF turns
northward.

How to cite: Raeder, J., Tulegenov, B., Cramer, W. D., Ferdousi, B., Fuller-Rowell, T., Maruyama, N., and Strangeway, R. J.: Polar Cap Boundary Reaction to Geomagnetic Storms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3173, https://doi.org/10.5194/egusphere-egu22-3173, 2022.

The solar wind couples with Earth’s magnetosphere driving plasma dynamics which can create magnetic perturbations at Earth’s surface impacting life on the ground. One classic way of understanding this process is via the Dungey cycle where magnetic flux is injected into the magnetosphere on the dayside via a dayside reconnection site. This flux is then transported downstream and is released from the magnetosphere via a tail reconnection site, bringing high hydrodynamic energy plasma earthward which becomes trapped in the ring current, leading to intense sustained magnetic perturbation.

In this work, we take a closer look at this process using 3D MHD results from the Space Weather Modeling Framework. Building off previous work by Brenner et al. 2021, the magnetopause surface is identified in the simulation domain to a fixed downstream tail distance. This 3D volume is then split into regions based on magnetic topology and L shell location. From here two methods are used to describe the magnetic perturbation resulting from each region. The first is using the Biot-Savart law that integrates current density vectors weighted by position and direction. The second uses the virial theorem which employs the scalar product of momentum with the position vector integrated over the magnetosphere. The latter formulation is advantageous since it directly relates the magnetic perturbation with stress terms at the magnetopause boundary and volume integrated energy density in the magnetosphere.

Results from the Biot Savart integration and virial theorem are compared with observations of ground based magnetic perturbations to study the effects of energy transport within the system during a simulated storm event.

How to cite: Brenner, A., Pulkkinen, T., Toth, G., Al Shidi, Q., and Liemohn, M.: Using the Virial Theorem to Analyze Effects of Energy Dynamics in the Magnetosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5549, https://doi.org/10.5194/egusphere-egu22-5549, 2022.

Numerical simulations play a central role in modern sciences. The trade-off between the accuracy of the physical processes described and the cost of computational resources is often the main limiting factor in these simulations. In global hybrid-Vlasov simulations, such as Vlasiator, lowering the spatial resolution in order to save on resources can lead to key processes being unresolved. A previous study has shown how insufficient resolution of the proton cyclotron instabilities leads to a misrepresentation of ion dynamics. This leads to larger temperature anisotropy and loss-cone shaped velocity distribution functions. In this study, we present a numerical model to introduce pitch-angle diffusion in velocity space, at a spatial resolution where this process was previously not correctly resolved. We test two different methods to enable pitch-angle diffusion in the 3D cartesian velocity space of Vlasiator. We show that we are successfully able to isotropise loss-cone shaped velocity distribution functions, and that this method could be applied to large simulations in order to save computational resources and still correctly model the Earth's magnetosheath.

How to cite: Dubart, M., Battarbee, M., Ganse, U., Spanier, F., Suni, J., Johlander, A., Alho, M., Bussov, M., Cozzani, G., George, H., Grandin, M., Manglayev, T., Papadakis, K., Pfau-Kempf, Y., Tarvus, V., Turc, L., Zaitsev, I., Zhou, H., and Palmroth, M.: Subgrid modelling of pitch-angle diffusion for ion-scale waves in a global hybrid-Vlasov simulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3429, https://doi.org/10.5194/egusphere-egu22-3429, 2022.

The precipitation of charged particles from the magnetosphere into the ionosphere is one of the crucial coupling mechanisms between these two regions of geospace. While precipitating particle fluxes have been measured by numerous spacecraft missions over the past decades, it often remains difficult to obtain global precipitation patterns with a good time resolution during a substorm. Numerical simulations can contribute to bridge this gap and help improve the understanding of mechanisms leading to particle precipitation at high latitudes through the global view they offer on the near-Earth space system. We present the first results on proton precipitation within a 3-dimensional simulation of the Vlasiator hybrid-Vlasov model. The run is driven by southward interplanetary magnetic field conditions with steady solar wind parameters. We analyse the large-scale proton precipitation pattern in both hemispheres and discuss its dynamics in relation to the processes taking place in the magnetotail.

How to cite: Grandin, M., Luttikhuis, T., Alho, M., Battarbee, M., Bussov, M., Cozzani, G., Dubart, M., Ganse, U., George, H., Horaites, K., Manglayev, T., Papadakis, K., Pfau-Kempf, Y., Suni, J., Tarvus, V., Turc, L., Zaitsev, I., Zhou, H., and Palmroth, M.: Proton precipitation in a hybrid-Vlasov simulation with southward interplanetary magnetic field driving: First 3D results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7611, https://doi.org/10.5194/egusphere-egu22-7611, 2022.

We investigate the dynamic coupling between the solar wind and Earth’s magnetosphere during northward IMF conditions. The high latitude lobe regions of the magnetosphere during such conditions are generally characterised as containing cool, very low energy plasma populations. However, when the solar wind is directed northward, hot plasma populations can sometimes be observed within the lobes, and transpolar arcs (auroral features which extend from the nightside into the polar cap) can also be present. We discuss three cases in which the Cluster spacecraft observed uncharacteristically energetic plasma populations in the lobe, with the footprint of the spacecraft intersecting a transpolar arc (Fryer et al., 2021). These observations reveal that both the hot plasma populations, and therefore transpolar arcs, are likely to form on closed field lines and are consistent with a mechanism in which magnetotail reconnection builds up closed field lines within the magnetotail, which then become “stuck” in the lobe (Milan et al., 2005).

Under certain northward IMF conditions, we find that the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS) model reproduces a similar large, closed field line region in the magnetotail. We find similarities between the structures seen within the simulation runs, the results of the in-situ observational study, and the Milan et al. (2005) magnetotail reconnection model, but also note some key differences in the configuration of the magnetotail reproduced in the simulations, compared with the remote and in situ observations. Finally, we note that the SMILE spacecraft will be ideally positioned to observe the coupling between the solar wind and Earth’s magnetosphere during northward IMF conditions, through both high latitude in situ observations and imaging of the auroral response.

How to cite: Fryer, L., Fear, R., Gingell, I., Coxon, J., Palmroth, M., Hoilijoki, S., Janhunen, P., and Kullen, A.: Observations and simulations of northward IMF magnetotail structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1177, https://doi.org/10.5194/egusphere-egu22-1177, 2022.

The solar wind’s embedded interplanetary magnetic field (IMF) impinging on the Earth’s magnetosphere has an impact on the terrestrial environment. The primary mechanism which allows for direct interaction between the solar wind and the terrestrial environment is magnetic reconnection on the Earth’s dayside between the IMF and the Earth’s magnetic field. Changes in the IMF result in a change of magnetic reconnection rates at the Earth’s dayside leading to changes in the auroral oval morphology/topology. The auroral oval is rather dynamic, and its variability is currently not well understood. We hypothesise that much of this variability is due to variations in ionospheric convection. We interpret its temporal and morphological variability in terms of ionospheric convection and dayside and nightside reconnection rates, (i.e., the "expanding/contracting polar cap" paradigm). Dayside reconnection is responsible for opening magnetic flux on the dayside and initiating ionospheric flows whereas nightside reconnection is ensuring closure of open magnetic field lines. In this study we infer convection patterns with SuperDARN (Super Dual Auroral Radar Network) measurements and ground-based magnetometers data (SuperMAG) using a new data assimilation technique. We combine convection flows with auroral precipitation patterns and solar wind parameters to understand the behavior of the auroral oval and the physical mechanisms that drive its dynamical changes. By examining both the dynamic evolution of the ionospheric convection and the corresponding dynamics of the colocated auroral forms seen in global UV images, we investigate to what extent convection can be associated with the changes observed in the large scale auroral boundaries in selected events. 

How to cite: Gasparini, S., Laundal, K. M., Reistad, J. P., Ohma, A., Hatch, S., and Elhawary, R.: The role of ionospheric convection in shaping the auroral oval, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7637, https://doi.org/10.5194/egusphere-egu22-7637, 2022.

We use an 18 year database of Super Dual Auroral Radar Network (SuperDARN) data to investigate the morphology of the large-scale ionospheric convection pattern. In particular, we look statistically at the location of the foci of the dawn and dusk convection cells which, according to the theoretical picture of Cowley and Lockwood (1992), are expected to move towards the dayside (nightside) when the Dungey cycle is dominated by magnetopause (magnetotail) reconnection. We use concurrent observations of the solar wind and interplanetary magnetic field to provide a proxy for the level of magnetopause reconnection and ground magnetic indices such as AL to provide an indication of the expected level of magnetotail reconnection. We find that, on average, the cell foci do move as predicted by the theory, but the presence of significant variability is consistent with additional factors being involved in governing the convection morphology at any given instant.

Cowley, S. W. H., and M. Lockwood (1992), Excitation and decay of solar wind-driven flows in the magnetosphere-ionosphere system, Ann. Geophysicae, 10, 103-115.

How to cite: Grocott, A. and Walach, M.-T.: Morphology of the ionospheric convection pattern during time-dependent solar wind and magnetospheric driving, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12309, https://doi.org/10.5194/egusphere-egu22-12309, 2022.

The interaction of the solar wind with the Earth’s magnetic field produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic field (IMF). While the dawn-dusk (By) component of the IMF is known to play an important role in this interaction, its effects are usually assumed to be independent of its sign. However, recent studies have shown that auroral electrojets and substorm activity are stronger for By < 0 in Northern Hemisphere (NH) summer. This so-called explicit By-dependence is reversed for NH winter. Here we study how IMF By modulates magnetospheric energetic protons and the ring current by using measurements of NOAA POES satellites and the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model coupled in with the global BATSRUS MHD code. We show that the energetic magnetospheric protons and the ring current (Dst index) exhibit an explicit By-dependence (stronger for By < 0 in NH summer), which can be reproduced by the model. Our results highlight the importance of the IMF By component for space weather and must be taken into account in the future space weather modeling.

How to cite: Holappa, L. and Buzulukova, N.: Explicit IMF By-dependence of magnetospheric energetic protons and the ring current, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11257, https://doi.org/10.5194/egusphere-egu22-11257, 2022.

Measurements from the Van Allen Probes mission clearly demonstrated that the radiation belts cannot be considered as a bulk population above approximately electron rest mass. Ultra-relativistic electrons (~>4Mev) form a new population that shows a very different morphology (e.g. very narrow remnant belts) and slow but sporadic acceleration.

We show that acceleration to multi-MeV energies can not only result of two-step processes consisting of local heating and radial diffusion but occurs locally due to energy diffusion by whistler-mode waves. Local heating appears to be able to transport electrons in energy space from 100s of keV all the way to ultra-relativistic energies (>7MeV) and is a dominant process for acceleration to ultra-relativistic energies. Acceleration to such high energies occurs only for the conditions when cold plasma in the trough region is extremely depleted down to the values typical for the plasma sheet.

There is also a clear difference between the loss mechanisms at MeV and multi MeV energies. The difference between the loss mechanisms at MeV and multi-MeV energies is due to EMIC waves, that can very efficiently scatter ultra-relativistic electrons, but leave MeV electrons unaffected.

These observations and modelling clearly show that cold plasma at eV energies has a controlling effect on the trapped electrons at energies seven orders of magnitude more energetic. Depletion in cold plasma is a requirement for acceleration while fast loss occurs only in the regions of high plasma density.

We also present how the new understanding gained from the Van Allen Probes mission can be used to produce the most accurate data assimilative forecast. Under the recently funded EU Horizon 2020 Project Prediction of Adverse effects of Geomagnetic storms and Energetic Radiation (PAGER) we will study how ensemble forecasting from the Sun can produce long-term probabilistic forecasts of the radiation environment in the inner magnetosphere.

How to cite: Shprits, Y. Y., Allison, H., Drozdov, A., Wang, D., Aseev, N., Zhelavskaya, I., and Usanova, M.: Controlling Effect of the Cold Plasma Density on Acceleration and Loss of Electrons at Ultra-Relativistic Energies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12946, https://doi.org/10.5194/egusphere-egu22-12946, 2022.