An Information-Theory Examination of the "Upstream-Turbulence Effect" in Solar-Wind/Magnetosphere Coupling

Simon Wing^1*Joseph E Borovsky²

• ¹Johns Hopkins University, Baltimore, United States
• ²Space Science Institute, Boulder, United States

Correlations of the amplitude of upstream solar-wind turbulence (as measured by the amplitude of magnetic-field fluctuations DB/B in the upstream solar wind) with increases in geomagnetic activity have been seen by many research groups. Recent doubt has been cast on whether or not this is a real cause-and-effect phenomenon. Using transfer entropy (TE) as a quantitative measure of causality, the present study demonstrates that turbulence exerts a real but weak influence on the magnetosphere, although it operates over long time scales. The information transfers from DB/B to AE and Dst are approximately an order of magnitude smaller and peak at larger response lag time (t) than the information transfer from Rquick and Newell solar wind coupling functions, which are primarily governed by reconnection term. In contrast, the information transfers from the solar wind velocity (Vsw) and DB/B to AE and Dst have peaks at comparable time scales. Thus, the information transfers from DB/B to AE and Dst look more similar to those from Vsw than to Rquick and Newell function, suggesting that the interaction between DB/B and the magnetosphere can be characterized as more viscous-like processes rather than reconnection driven. Nevertheless, although both DB/B and Vsw interact with the magnetosphere through viscous mechanism, DB/B exhibits lower geoeffectiveness. The information transfer from DB/B to AE is approximately 45% of that from Vsw while the information transfer from DB/B to Dst is an order of magnitude smaller than that from Vsw. The results suggest that solar wind turbulence affects various magnetospheric regions and phenomena differently.