ST 2020 Hannes Alfvén Medal Lecture & 2021 Julius Bartels Medal Lecture & 2020 Division Outstanding ECS Award Lecture
Convener: Olga Malandraki
| Fri, 23 Apr, 15:00–17:00 (CEST)

Presentations: Fri, 23 Apr

Chairperson: Olga Malandraki
ST Division Outstanding ECS Award Lecture 2020
Lauri Holappa, Timo Asikainen, and Kalevi Mursula

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 By component. However, recent studies have shown that IMF By is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for By > 0 (By < 0). For NH summer the dependence on the By sign is reversed. We quantify the size of this explicit By-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 By > 0 than for By < 0 in NH winter. We also discuss recent advances in the physical understanding of the By-effect. Our results highlight the importance of the IMF By-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,, 2021.

Hannes Alfvén Medal Lecture 2020
Qiugang Zong

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,, 2021.

Julius Bartels Medal Lecture 2021
Volker Bothmer

Magnetic clouds are transient solar wind flows in the interplanetary medium with smooth rotations of the magnetic field vector and low plasma beta values. The analysis of magnetic clouds identified in the data of the two Helios spacecraft between 0.3 and 1 AU showed that they can be interpreted to first order by force-free, large-scale, cylindrical magnetic flux tubes. A close correlation of their occurrences was found with disappearing filaments at the Sun. The magnetic clouds that originated from the northern solar hemisphere showed predominantly left-handed magnetic helicities and the ones from the southern hemisphere predominantly right-handed ones. They were often preceded by an interplanetary shock wave and some were found to be directly following a coronal mass ejection towards the Helios spacecraft as detected by the Solwind coronagraph on board the P78-1 satellite. With the SOHO mission unprecedented long-term observations of coronal mass ejections (CMEs) were taken with the LASCO coronagraphs, with a spatial and time resolution that allowed to investigate their internal white-light fine structure. With complementary photospheric and EUV observations from SOHO, CMEs were found to arise from pre-existing small scale loop systems, overlying regions of opposite magnetic polarities. From the characteristic pattern of their source regions in both solar hemispheres, a generic scheme was presented in which their projected white-light topology depends primarily on the orientation and position of the source region’s neutral line on the solar disk. Based on this interpretation the graduated cylindrical shell method was developed, which allowed to model the electron density distribution of CMEs as 3D flux ropes. This concept was validated through stereoscopic observations of CMEs taken by the coronagraphs of the SECCHI remote sensing suite on board the twin STEREO spacecraft. The observations further revealed that the dynamic near-Sun evolution of CMEs often leads to distortions of their flux rope structure. However, the magnetic flux rope concept of CMEs is today one of the fundamental methods in space weather forecasts. With the Parker Solar Probe we currently observe for the first time CMEs in-situ and remotely at their birthplaces in the solar corona and can further unravel their origin and evolution from the corona into the heliosphere. This lecture provides a state-of-the-art overview on the magnetic structure of CMEs and includes latest observations from the Parker Solar Probe mission.

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,, 2021.