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Observations and modelling of the effects of solar wind pressure pulses on the terrestrial magnetosphere

Positive solar wind pressure pulses are pockets of solar wind plasma that are faster and/or denser than the surrounding ambient plasma. When a pressure pulse impacts the terrestrial magnetosphere, it is rapidly compressed, and the effects propagate inwards resulting in a well observed enhancement in the magnetic field, as evidenced in the SYM-H index; this communication of a pressure pulse into the magnetosphere is known as a geomagnetic sudden commencement (SC). SCs can be further subdivided into sudden impulses (SIs) and sudden storm commencements (SSCs), where in the latter case, the pressure pulse triggers a geomagnetic storm. Even for small, short lived, pressure enhancements, the effects on the terrestrial magnetosphere can be dramatic, exciting and even reconfiguring the electrodynamics within. Among these effects, observations and modelling have shown: enhancements and restructuring of high latitude ionospheric currents and convection; auroral emission excited by particle precipitation; energisation of the plasmasphere; excitation of magnetospheric current systems; enhanced ULF wave activity.
In this session, we invite contributions based on both observations and modelling of the effect of solar wind pressure pulses on the coupled solar wind – magnetosphere – ionosphere system. We seek to facilitate crossover discussion between the observational and modelling communities on pressure pulse driving of phenomena including (but not limited to): ULF wave propagation; ionospheric convection; ionospheric and magnetospheric current systems; auroral emission; terrestrial radio emissions; plasmasphere effects.

Convener: Alexandra FoggECSECS | Co-conveners: Thomas ElsdenECSECS, Mark Lester
| Thu, 26 May, 14:05–14:50 (CEST)
Room 1.14

Thu, 26 May, 13:20–14:50

Chairperson: Alexandra Fogg

Virtual presentation
Andy Smith et al.

The impact of a solar wind pressure pulse on the Earth’s magnetosphere causes rapid changes in the surface geomagnetic field, often termed Sudden Commencements (SCs).  Such magnetic field changes can induce potentially damaging currents (GICs) in conducting infrastructure on the ground, and therefore represents a critical space weather hazard.  Unfortunately, GICs are not often measured directly.  Instead, large GICs are often inferred from easier-to-measure large magnetic perturbations.  In this work we examine the coupling between SCs and observed GICs in New Zealand, where both measurements are available.

Overall, we find excellent correlations between the maximum magnetic perturbations and GICs during SCs. Nevertheless, if the SC precedes a geomagnetic storm, then it is associated with 22% larger GICs, controlling for the size of the magnetic deflection.  Further, if the SC is observed when New Zealand is on the dayside of the Earth then the associated GICs are 30% greater.  We investigate these findings, and attribute them to the full vector directionality of the strongest magnetic field deflection and the full rate of change of the magnetic field of the SC, beyond that recorded in the one minute resolution data.

Finally, we show that based on the properties of the solar wind shock, a skilful prediction can be made as to whether an SC and/or a geomagnetic storm will be observed, which may be used to guide interpretation of the coupling between the magnetic deflection and GICs.

How to cite: Smith, A., Rodger, C., Mac Manus, D., Forsyth, C., Rae, J., Freeman, M., Clilverd, M., Petersen, T., and Dalzell, M.: The Correspondence between Sudden Commencements and Induced Currents; Insights from New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1358, https://doi.org/10.5194/egusphere-egu22-1358, 2022.

Virtual presentation
Osuke Saka and Dmitri Klimushkin

Dawn-dusk flow shears in the nightside magnetosphere associated with field line dipolarization produce tangential discontinuities in the midnight sector and generate periodic displacement of the discontinuity surface at Pi2 periodicities through the KH instabilities [Saka et al., 2010].

Wave polarizations of Pi2 pulsations thus produced in the magnetosphere by the boundary displacement are generally reversed in the polar ionosphere [Saka et al., 2012]. The polarization reversal cannot be understood through the reconfiguration of geomagnetic field lines in terms of the fundamental harmonics but rather by considering the third harmonics in the meridian planes. On the ground, negative bays marked by decrease of the northward component of the geomagnetic fields are observed. We show that the field line deformations associated with third harmonics matched those of field line dipolarization and they are produced by the poloidal wave mode guided along the field lines: guided poloidal mode [Radoski, 1967]. This result indicates that Pi2 pulsations in meridian plane are field line dipolarization itself excited at the outer boundary of closed magnetosphere.



Radoski, H., Highly asymmetric MHD resonances: the guided poloidal mode, J. Geophys. Res., 72, 4026, 1967.

Saka,O., Hayashi, K., and Thomsen, M., First 10 min intervals of Pi2 onset at geosynchronous altitudes during the expansion of energetic ion regions in the nighttime sector, J. Atmos. Solar Terr. Phys., 72, 1100, 2010.

Saka, O., K. Hayashi, and D. Koga, Excitation of the third harmonic mode in meridian planes for Pi2 in the auroral zone. J. Geophys. Res., 117, A12215, doi:10.1029/2012JA018003, 2012.

How to cite: Saka, O. and Klimushkin, D.: Are Pi2 pulsations in meridian plane a field line dipolarization?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1026, https://doi.org/10.5194/egusphere-egu22-1026, 2022.

Konstantinos Horaites et al.

Vlasiator (https://www2.helsinki.fi/en/researchgroups/vlasiator) is a high-performance kinetic code that is now conducting the first ever 3D hybrid-Vlasov simulations of the global magnetospheric system. In recent months, the driving conditions of these simulations have been scaled up to emulate intense space weather events. Specifically, we have investigated the impact of a pressure pulse with southward-oriented Bz on the Earth's magnetosphere. Our simulations reproduce many known effects, for example the expansion of the auroral oval, compression of the magnetopause, the development of field-aligned currents, and enhanced particle precipitation near the open/closed field line boundary. We compare our data with spacecraft observations of real events that exhibit similar parameters to those imposed in the simulation. Our analysis shows that the hybrid-Vlasov approach captures many of the important aspects of the magnetospheric response to an incoming pressure pulse. With sufficient validation of our simulations by comparison with moderate storms, we aim to show that Vlasiator can be used as a tool to study even the most extreme events and their potential impacts on Earth's critical infrastructure.

How to cite: Horaites, K., Alho, M., Battarbee, M., Dubart, M., Ganse, U., George, H., Grandin, M., Manglayev, T., Palmroth, M., Papadakis, K., Suni, J., Tarvus, V., Turc, L., Zaitsev, I., and Zhou, H.: Three-dimensional Hybrid-Vlasov Simulations of Geomagnetic Storms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4687, https://doi.org/10.5194/egusphere-egu22-4687, 2022.

Impact of the solar wind dynamic pressure on field-aligned currents in the magnetotail: Cluster observation 
Jiankui Shi et al.
James Waters et al.

Auroral Kilometric Radiation (AKR) is terrestrial radio emission that originates from high latitude magnetic field lines. The intensity of AKR increases when the magnetosphere is perturbed, and so can indicate the presence of driving from the solar wind. This is true for structures that can vary in scale such as pressure pulses, as well as substorm onsets that follow periods of negative turnings in the Z component of the interplanetary magnetic field. In the latter case, AKR intensification correlates with the strengthening of high-latitude current systems in the ionosphere as the magnetotail current is reconfigured. As well as this, morphological changes in the AKR source region have also been observed to coincide with substorm onset, with an intensification of the AKR emission often accompanied by a low frequency extension, interpreted as an expansion of the source region to higher altitudes along the field line. Although the directivity and source region localisation of AKR make the observations highly dependent on observer local time and latitude, we isolate AKR from Wind radio observations made over a decade and examine the observations with respect to the spacecraft viewing position, accounting for such effects. Using lists of substorm onsets, we examine the AKR power and the spectral extent of the emission with respect to the substorm timeline, expanding on previous studies of the AKR response. Results show a clear increase in AKR power that precedes substorm onset by approximately 20 minutes, and confirm a proportionally higher intensification in lower frequency AKR sources. This in turn indicates quantitatively the spatial response of parallel electric fields after the loading of magnetic flux during substorm growth phase. In characterising the typical AKR response during substorms, these results can inform observations of magnetospheric changes during sudden commencement events and those that are seperate from substorm dynamics.

How to cite: Waters, J., Jackman, C., Whiter, D., Forsyth, C., Fogg, A., Lamy, L., Cecconi, B., Bonnin, X., and Issautier, K.: A perspective on substorm dynamics from 10 years of Auroral Kilometric Radiation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8149, https://doi.org/10.5194/egusphere-egu22-8149, 2022.

Virtual presentation
Salih Mehmed Bostan et al.

Solar wind pressure pulses are known to modify electrodynamics of the terrestrial magnetosphere. In this paper, we present a possible electrodynamic reaction of the ionosphere to a small and brief pressure pulse observed by local and non-local instrument systems over Arecibo Observatory, Puerto Rico and extending over at least the mesoscale. Initially, a strong, four hour long, mid-latitude spread-F-like event was observed through a high frequency, wide-beam radar system, Penn State Ionospheric Radar Imager (PIRI), deployed near Arecibo (18.36◦ E, 66.75◦ S, and f = 4.42 MHz). The same spread-F event was also observed using the dual, narrow-beam 430 MHz Arecibo incoherent scatter radar. Furthermore, GPS delta-vTEC measurements from Carribean island sector revealed that the event was apparently moving from west to east and then east to west crossing over Arecibo twice. Similar GPS-TEC measurements from the South American sector showed that an equatorial spread-F was also present. We use SuperMAG magnetometer and NASA’s OMNI solar wind data to show that a small solar wind pressure pulse and rapid changes in the solar wind magnetic field are likely causes for the observed ionospheric features over Arecibo.

How to cite: Bostan, S. M., Urbina, J. V., Mathews, J. D., and Dinsmore, R. L.: A Non-Local Spread-F-like Event Over Arecibo as the Possible Result of a Solar Wind Pressure Pulse, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10089, https://doi.org/10.5194/egusphere-egu22-10089, 2022.

Virtual presentation
Bohdan Petrenko et al.

The flapping motion of the magnetotail current sheet has a valuable contribution to magnetosphere dynamics. We have investigated features of flapping motions involving single- and multi-spacecraft methods using MMS and Cluster measurements. Velocities of dawn-dusk propagation of these motions and their types have been determined using Harris current sheet model and minimum variance analysis of the magnetic field. Dispersion features of such wavy motions using the phase differencing technique were explored.             

This work was carried out in accordance with the Target Comprehensive Program of the SRI NASU and SSAU in plasma physics with the support of grant no. 97742 of the Volkswagen Foundation (VW-Stiftung). 

How to cite: Petrenko, B., Kozak, L., Kronberg, E., and Grigorenko, E.: Multispacecraft wave diagnostics of the flapping motion of the magnetotail current sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11431, https://doi.org/10.5194/egusphere-egu22-11431, 2022.

Reko Hynönen and Eija Tanskanen

Pc5 waves are a sub-group of ultra-low frequency (ULF) waves in the magnetosphere. We determine the Pc5 wave power from ground magnetometer measurements in IMAGE network and statistically study their dependence on solar wind conditions, like solar wind speed and dynamic pressure, separating them from the solar phase and solar conditions in a statistical sense.

Pc5 power is dependent on the magnetic local time, season, and magnetic latitude. We show that while it is always heavily modulated by solar wind speed, the intensity of its ground response also varies over time. Particularly, the ground response is usually the strongest in the morning and midnight hours, while a minor maximum can sometimes be found in the midday or afternoon hours.

How to cite: Hynönen, R. and Tanskanen, E.: Ground response of seasonal Pc5 power to varying solar wind conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12854, https://doi.org/10.5194/egusphere-egu22-12854, 2022.