Temporal variation of solar wind in controlling solar wind-magnetosphere-ionosphere energy budget

It is not yet known how the solar wind oscillation frequency, and thus its temporal variation, regulates the energy flow through the coupled solar wind-magnetosphere-ionosphere-thermosphere system. Utilizing the Coupled Magnetosphere-Ionosphere-Thermosphere Model driven by solar wind and interplanetary magnetic field (IMF), we have analyzed the magnetosphere-ionosphere-thermosphere system response to IMF B-z oscillations with periods of 10, 30, and 60 min from the perspective of energy budget.

Our results indicate that the energy flow from the solar wind to geospace depends on the IMF B-z oscillation frequency. The energy coupling efficiency, defined as the ratio of the globally integrated joule heating to Akasofu's Epsilon function, is higher for lower frequency IMF B-z oscillations. Joule heating in the upper atmosphere depends not only on directly driven processes due to solar wind variability but also on the intrinsic dynamics of the magnetosphere (i.e., loading-unloading process).