Solar Wind-Magnetosphere Energy Coupling: Directly Drive or Loading- Unloading

The most direct response of the Earth's magnetosphere and ionosphere to the solar wind energy input is seen in the high latitude ionosphere as increased auroral activity, ionospheric convection and joule heating etc. These reactions are operated by same and/or different mechanisms. Then, interesting questions include with the same solar wind source why the reaction can be so different? What determines the energy transfer budget of each reaction? If one reaction (such as the auroral intensity enhancement) is caused by more than one magnetospheric disturbances (such as subtorms and storms), can we distinguish corresponding energy depositions, respectively? Recently, we have expanded the Natural Orthogonal Component (NOC) method to the separation of the ionospheric electric field (Sun et al., GRL, 2008; Zhou et al., submitted to Adv. Geosci, 2008) based on the AMIE potential data. We have successfully separated nightside ionospheric electric fields that are the Directly Driven (DD) component (a westward electric field, EW) and the Loading-Unloading (UL) component (a southward electric field, ES). The latter represents substorm expansion phase (SEP). In this study, we calculate energy depositions corresponding to the two processes, respectively. The intensity and location of Joule heating are quantitatively depicted in two dimensions. Whether the DD process is a substorm or is more adequate for a magnetospheric convection will be discussed.