University of Maryland
4:30 PM Monday, September 28, 2020

Nat Gopalswamy
Solar Physics Laboratory, NASA Goddard Space Flight Center

On the Role of Shocks in Understanding Solar and Heliospheric Phenomena

Fast-mode MHD shocks were inferred from radio bursts from the Sun and from geomagnetic storm sudden commencement (SSC) more than six decades ago. Now we know that they are key players in Sun-Earth connection: they produce large solar energetic particle events and energetic storm particle events, cause SSC/sudden impulse compressing the magnetosphere, causing the onset of geomagnetically induced currents, contributing to energetic particles in the Earth's magnetosphere, and even modifying the atmospheric chemistry. Shocks are now observed throughout the heliosphere by remote-sensing and in-situ observations. This talk will address some of the recent achievements in understanding solar and heliospheric phenomena involving shocks. In particular, I will use the large data base on type II radio bursts observed by the Radio and Plasma Wave (WAVES) experiment onboard the Wind spacecraft and the simultaneously available coronal mass ejection (CME) data from the Solar and Heliospheric Observatory (SOHO) mission over the past quarter century. I will address the relation to SEP events, which have led to the understanding of when where the highest-energy particles are accelerated. I will also touch upon the new result that the large-scale nature of the interplanetary shocks may be the source of high-energy (>100 MeV) gamma-rays lasting for hours beyond the end of the associated solar flares.