Calculation of the Relativistic Electron flux at Geostationary Orbit Due to an Extreme Space Weather Event

Abstract:

Fast solar wind stream events emanating from coronal holes on the Sun have been responsible for some of the highest relativistic electron flux enhancements at geostationary orbit. Here we develop a reasonable worst case event and calculate the electron flux using a physical model in order to help assess radiation exposure to satellites. We present a statistical analysis of chorus wave data for fast solar wind streams and select an event lasting up to 5 days. We solve a 2d Fokker-Planck equation which includes substorm injections, chorus wave acceleration and losses to the atmosphere. We show that after a period of five days the integral flux greater than 2 MeV can increase by several orders of magnitude. We show that the resulting flux is most sensitive to the distribution of chorus wave power and the ratio of the electron plasma to cyclotron frequencies and relatively insensitive to the presence of a pre-existing electron radiation belt. The model predicts an electron flux at geostationary orbit that can result in a charging current that exceeds the NASA recommended guidelines for triggering an internal electrostatic discharge. Thus we would expect many satellites to report anomalies with a strong likelihood of service outage and total satellite loss during an extreme space weather event driven by a fast solar wind stream.