Twenty one differences between CME-driven geomagnetic storms and CIR-driven geomagnetic storms are tabulated. (CME-driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; CIR-driven includes driving by the associated recurring high-speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME-driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR-driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR-driven storms than it is prior to CME-driven storms. CME-driven storms pose more of a problem for Earth-based electrical systems; CIR-driven storms pose more of a problem for space-based assets.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JA011447

Differences between CME‐driven storms and CIR‐driven storms

Ultra-low frequency (ULF; approx. 1 mHz ≤ f ≤ 10 Hz) MHD plasma waves are readily recorded throughout the Earth’s magnetosphere and on the ground. Generated by a variety of instabilities, ULF waves transport and couple energy throughout the system, and may play important roles in the energization and loss of radiation belt particles. ULF waves also provide a convenient probe and diagnostic monitor of the magnetosphere. The availability of multipoint measurements from spacecraft, ionospheric sounders and ground magnetometer arrays and the increasing sophistication of modeling tools have stimulated much recent progress in this area. Nevertheless, fundamental questions remain regarding the generation, propagation and consequences of these waves. This chapter reviews recent developments in these areas.

Magnetospheric ULF Waves: A Review

We study the effect of interplanetary coronal mass ejection (ICME)-driven sheath regions on relativistic outer radiation belt electron fluxes. We employ superposed epoch analysis, and, unlike previous studies, we segregate the sheath from the ejecta. We find that sheaths typically result in more than an order of magnitude decrease in the relativistic electron fluxes and that the fluxes stay below the pre-event level for more than 2 days after the sheath passage. The electron depletions are stronger for sheaths that exhibit higher power in magnetic and dynamic pressure fluctuations in the ultralow frequency range and cause larger magnetospheric compressions. Depletions are even stronger for sheaths that encompass the entire storm main phase. Our findings suggest that sheaths are effective at depleting the electron fluxes because they increase radial diffusion under magnetospheric compression conditions, thereby enhancing magnetopause shadowing losses, particularly when the Dst effect can act in concert.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014GL059551

Depleting effects of ICME-driven sheath regions on the outer electron radiation belt

[1] The primary purpose of this paper is to show the importance of solar wind excitation as a source of magnetospheric and ground Pc5 fluctuations. In particular, we show that pressure fluctuations, a nearly ubiquitous feature of the solar wind, drive magnetospheric compressional Pc5, whose amplitude and power increase in direct proportion to the amplitude and power of the solar wind pressure fluctuations. Previous studies of compressional Pc5 have focused primarily on internally generated waves on the dusk flank; here we highlight the pressure fluctuations associated with geoeffective high-speed streams (HSSs) and interplanetary coronal mass ejections (ICMEs) during a time interval in March and April 2002, in the declining phase of the solar cycle, when there was a favorable alignment of satellites. Using three examples and a statistical survey, we show that for this time interval external forcing due to solar wind dynamic pressure fluctuations was dominant over internal forcing. Fluctuations driven by internal processes, occurring primarily at dusk and on the nightside, accounted for less than 20% of the total power. We also found that multiple external forcing processes were occurring during this interval, including evanescent propagation of compressional waves, field line resonance (FLR), and global mode excitation. We need to enlarge our vision of the source of ULF waves to include excitation by solar wind pressure fluctuations as a significant factor.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007JA012255

Solar wind excitation of Pc5 fluctuations in the magnetosphere and on the ground

High-speed solar wind streams originating from large coronal holes reached a maximum in 2003 during the descending phase of solar cycle 23. At the same time, magnetic activity (as indicated by the aa index) reached the highest levels of the last four solar cycles. The rotation of active regions behind the limb and the appearance of coronal holes contribute to a decrease in EUV radiation at Earth prior to the arrival of a high-speed stream. This leads to a cooling of the upper atmosphere and a decrease in the total electron content (TEC). Changes in ΣO/N 2 are also expected but contributions from local time and seasonal changes as the satellite orbit precesses during a solar rotation will require additional simulations to unravel. These systematic changes are intriguing because auroral disturbances expand further equatorward in latitude and deeper in altitude as F10.7 decreases. Disturbances in nitric oxide (NO), the dominant cooling agent in the upper atmosphere, continue for the duration of the high-speed stream activity and may not fully recover before the next stream hits. These disturbed conditions might actually represent the most common state of the upper atmosphere in years of strong recurrent high-speed streams. Finally, the persistent source of thermospheric NO in the auroral region during high-speed streams, when combined with favorable meteorological conditions in the dark polar middle atmosphere, results in significant enhancements in stratospheric NO X . These correspond to increases in stratospheric ozone loss, establishing a previously unexplored link between high-speed streams and stratospheric variability.

Response of the Upper/Middle Atmosphere to Coronal Holes and Powerful High‐Speed Solar Wind Streams in 2003

. We show a clear correlation between the ULF wave power (Pc5 range) inside and outside the Earth's magnetosphere during high speed streams in 1995. We trace fluctuations beginning 200RE upstream using Wind data, to fluctuations just upstream from Earth's bow shock and in the magnetosheath using Geotail data and compare to pulsations on the ground at the Kilpisjarvi ground station. With our 5-month data set we draw the following conclusions. ULF fluctuations in the Pc5 range are found in high speed streams; they are non-Alfvenic at the leading edge and Alfvenic in the central region. Compressional and Alfvenic fluctuations are modulated at the bow shock, some features of the waveforms are preserved in the magnetosheath, but overall turbulence and wave power is enhanced by about a factor of 10. Parallel (compressional) and perpendicular (transverse) power are at comparable levels in the solar wind and magnetosheath, both in the compression region and in the central region of high speed streams. Both the total parallel and perpendicular Pc5 power in the solar wind (and to a lesser extent in the magnetosheath) correlate well with the total Pc5 power of the ground-based H-component magnetic field. ULF fluctuations in the magnetosheath during high speed streams are common at frequencies from 1–4mHz and can coincide with the cavity eigenfrequencies of 1.3, 1.9, 2.6, and 3.4mHz, though other discrete frequencies are also often seen. Key words. Interplanetary physics (MHD waves and turbulence) – Magnetospheric physics (solar wind-magnetosphere interactions; MHD waves and instabilities)

https://angeo.copernicus.org/articles/22/629/2004/angeo-22-629-2004.pdf

R. L. Kessel

Papers

Correlation of Pc5 wave power inside and outside themagnetosphere during high speed streams