A Study of Auroral Energy Behavior During HILDCAA Events

It is possible to identify geomagnetic storms and substorms with geomagnetic indices. By analysing Dst and AE, Tsurutani and Gonzalez (1987) defined a category of events called High-Intensity, Long-Duration, Continuous AE Activity, or HILDCAA. During these events, the AE index must reach, at least, 1000 nT, and never fall bellow 200 nT for more than 2 hours at a time. These conditions must last for at least 2 days, and must occur outside main phases of magnetic storms. In this paper, we focus our attention to this class of events. During the period 1998 to 2001, 14 HILDCAAs have been identified. Our main interest is to investigate how energy transfer occurs between solar wind and magnetosphere during HILDCAA events. One form of investigating this transfer energy is through the Hemispheric Power (HP), an estimate of the energy of all particles precipitating into a hemisphere. HP is obtained by comparing the energy flux observed along an orbital track of a NOAA/TIROS spacecraft. We analyze the time profile of the auroral particle precipitation energy in parallel with the time variation of geomagnetic indices for the 14 HILDCAA events. For each selected event we obtain correlation coefficients between the HP and the AE time series. The comparison was chosen since HP is a measurement of particles precipitation and AE index can be used as a proxy for the auroral energy deposition and Joule heating. Preliminary results indicate that HP and AE show similar behavior of the time evolution during HILDCAAs indicating the two are closely related. Similar analysis has also been carried out for magnetic storms to study how energy dissipation processes are different during these processes.