Auroral hemispheric power during geomagnetic storms driven by different interplanetary disturbances

Although it has been a long time since the beginning of research on the auroral hemispheric power (HP), less has been done on the differences of HP among storms driven by different interplanetary disturbances. According to different drivers, all the storm events during 2001-2008 are divided into three categories, namely helmet streamer corotating interaction regions (CIRs), pseudostreamer CIRs and interplanetary coronal mass ejection(ICMEs) driven events. A superposed epoch analysis is performed to investigate the relative differences of HP during geomagnetic storms driven by different disturbances. The background solar wind parameters, geomagnetic activity and the effectiveness of coupling function have been studied. In addition, we have investigated the hemispheric asymmetry of HP in the three types of storms. The statistic results show that HP favors storms driven by pseudostreamer CIRs and ICMEs than storms driven by helmet streamer CIRs before the storm onset. It is inferred that the occurring of the so-called "calm before the storm" effect is less correlated with the Russell-McPherron effect, but might be a result of the Newell coupling function. The maximum of HP during helmet streamer CIR storms is greater than that during pseudostreamer CIR and ICME storms. The possible reason is larger interplanetary magnetic field component vertical bar B-z vertical bar and higher solar wind number density related to helmet streamer CIRs. The difference value of HP between two hemisphere(winter minus summer) increases with Kp when Kp is less than or equal to 4, which is consistent with the prediction of the ionospheric conductivity feedback model. For Kp>4, HP favors winter hemisphere during storms driven by helmet streamer CIRs and ICMEs, but summer HP is larger or close to winter HP during storms driven by pseudostreamer CIRs.