What is a radiation belt enhancement event?

Abstract:

Statistical studies of radiation belt enhancement events typically rely on other observations to define an “event”. Those other observations could be based on Dst, solar wind speed, CME or CIR occurrence, etc. It is also interesting to start with an electron event and ask which geomagnetic or solar wind driving conditions are (or are not) related to those events. However, such studies have been hindered by the absence of a uniform, quantitative definition of “events”. This is particularly true in phases of the solar cycle where background radiation belt fluxes are low but relative changes are large. Such events would be missed by picking an arbitrary flux threshold to define events. We examine two solar cycles of geosynchronous measurements to define the probability distribution of events with both fixed and solar cycle-dependent event criteria. These distributions allow us to define events based on radiation belt electron data alone, to classify types of enhancement events, and to ask: What conditions produced that class of events? The same distributions have important space weather forecasting applications as well. We can now quantify the criteria that define enhancement events that can be expected to occur once per month, once per year, or once per solar cycle.