GEM: Phase Space Density Gradient of Energetic Electrons at Geosynchronous Orbit During Sharp Solar Wind Pressure Enhancements

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). A major objective of the Geospace Environment Modeling (GEM) Focus Group on Space Radiation Climatology is to investigate the relationships between interplanetary conditions and trapped radiation belt particles and how these relationships change on long time scales (over a solar cycle) and apply this knowledge to the development of inner magnetospheric components of a Geospace General Circulation Model (GGCM). It is known that magnetic storms vary with solar wind conditions and that magnetospheric energetic particles have their largest variations during magnetic storms. However, the origin of radiation belt particles is still not fully understood and that has made it difficult to understand the physical mechanisms controlling the variability of these particles. The radial profile of the phase space density (PSD) of the radiation belt electrons for the first and second adiabatic invariants can provide insight of the source and the acceleration mechanisms. However, such a PSD radial profile is often difficult to obtain, mainly because of the lack of multipoint measurements and reliable magnetic field models with temporal scales on the order of 10 minutes, the drift period of a 1 MeV electron near geosynchronous orbit. This project is a two year research effort to determine the location of the energetic particle heating region by measuring the radial gradient of the PSD of energetic electrons and ions at and beyond geosynchronous orbit prior to and immediately after sharp solar wind pressure enhancements. From these measurements one can obtain the PSD at different radial distances prior to the solar wind pressure enhancements. Test-particle simulations will be performed to validate the PSD analysis and provide an estimate of the actual position of the particles before the arrival of the solar wind pressure enhancement. Sharp solar wind pressure enhancements, which can be due to interplanetary shocks and high speed solar wind streams, occur throughout the solar cycle. A statistical survey over a long term (approximately 1.5 solar cycles) will reveal any solar cycle and seasonal dependencies of the radial gradient.