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). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so-called IMF clock angle in a way, which is symmetric with respect to the sign of the B_y component. However, recent studies have shown that IMF B_y is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for B_y > 0 (B_y < 0). For NH summer the dependence on the B_y sign is reversed. We quantify the size of this explicit B_y-effect with respect to the solar wind coupling function, both for northern and southern high-latitude geomagnetic activity. We show that for a given value of solar wind coupling function, geomagnetic activity is about 40% stronger for B_y > 0 than for B_y < 0 in NH winter. We also discuss recent advances in the physical understanding of the B_y-effect. Our results highlight the importance of the IMF B_y-component for space weather and must be taken into account in future space weather modeling.

How to cite: Holappa, L., Asikainen, T., and Mursula, K.: Explicit IMF By-dependence in geomagnetic activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-850, https://doi.org/10.5194/egusphere-egu21-850, 2021.

Solar wind forcing, e.g. interplanetary shock and/or solar wind dynamic pressure pulses impact on the Earth’s magnetosphere manifests many fundamental important space physics phenomena including producing electromagnetic waves, plasma heating and energetic particle acceleration. This paper summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma physic based on in situ spacecraft measurements, ground-based magnetometer data, MHD and kinetic simulations.

Magnetosphere response to solar wind forcing, is not just “one-kick” scenario. It is found that after the impact of solar wind forcing on the Earth’s magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change of interplanetary shock or solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to generate series kind of waves including poloidal mode ultra-low frequency (ULF) waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region response to the impact usually contain two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression; (2) followed by the wave-particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells.

Generalized theory of drift and drift-bounce resonance with growth or decay localized ULF waves have been developed to explain in situ spacecraft observations. The wave related observational features like distorted energy spectrum, boomerang and fishbone pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the frame work of this generalized theory. It is worthy to point out here that poloidal ULF wave is much more efficient to accelerate and modulate electrons (fundamental mode) in the radiation belt and charged ions (second harmonic) in the ring current region. The results presented in this paper can be widely used in solar wind interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune, and other astrophysical objects with magnetic fields.

How to cite: Zong, Q.: Magnetospheric Response to Solar Wind Forcing: ULF Waves – Particle interaction Perspective , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-529, https://doi.org/10.5194/egusphere-egu21-529, 2021.

How to cite: Bothmer, V.: The magnetic flux rope structure of coronal mass ejections – 2021 Julius Bartels Medal Lecture at vEGU, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11152, https://doi.org/10.5194/egusphere-egu21-11152, 2021.