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Long‐term variations in solar wind velocity and radiation belt electrons
Author(s) -
Reeves Geoff,
Morley Steve,
Cunningham Greg
Publication year - 2013
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/jgra.50126
Subject(s) - van allen radiation belt , solar wind , solar maximum , space weather , solar cycle , physics , atmospheric sciences , magnetosphere , solar cycle 22 , solar minimum , environmental science , meteorology , wind speed , plasma , quantum mechanics
In this paper we analyze the relationship between yearly variations in MeV radiation belt electron fluxes and solar wind velocity (Vsw). We find that the long‐term trends have properties that are important for physical understanding of solar wind‐magnetosphere coupling processes and, potentially, for improvements of short‐term space weather forecasts. A statistical analysis of solar wind velocity shows that years with high average solar wind velocity are not high simply due to a larger number of days with high Vsw. Rather the entire distribution (median and percentiles) shifts along with the mean Vsw. Similar behavior is seen in the MeV geosynchronous electron fluxes. By subtracting out a 365 day running average baseline, we show that the distribution of log fluxes around the mean is remarkably stable from year to year within a solar cycle and from one solar cycle to another. In contrast, the long‐term trends in the baseline show significant changes from year to year and from one solar cycle to another suggesting that solar wind coupling to radiation belt fluxes is not constant but varies over long, as well as short, time scales. In some epicycles, the mean flux is strongly dependent on Vsw while in others the dependence is weak. Similarly, a given average Vsw may produce high average fluxes in one epicycle and low average fluxes in another. Future study of these epicycles and the relative variations within them may improve both physical understanding of solar wind‐magnetosphere coupling and space weather forecasting.