HILDCAA* events between 1998 and 2007 and their related interplanetary magnetic field and plasma values

Abstract

We investigate the interplanetary conditions during 135 less strict high-intensity, long-duration, continuous AE activity (HILDCAA*) events between the years 1998-2007. The HILDCAA* events were chosen by following the three "traditional" criteria which describe the high-intensity, long-duration, continuous AE activity (HILDCAA). However, we include a small modification in the criteria that considers: "the AE values do not drop below 200 nT for more than 2 h at a time". This criteria is modified by changing 2 to 4 hours period in which the AE values should not drop below 200 nT. Once the events are selected, we perform a statistical analysis of the interplanetary parameters during their occurrences. The distribution of HILDCAA* events along the solar cycle shows a pattern of double peak, with a peak around the maximum of the sunspot cycle, and an other in the descending phase. This kind of distribution is similar to the distribution of low-latitude coronal holes. For each of the HILDCAA* events, we have found its related Interplanetary Magnetic Field (IMF) and plasma parameter signatures. The average values of AE, AU, AL, and Dst indices, the density and temperature of the solar wind protons, the solar wind speed, the Bz component of the IMF, the IMF intensity, dynamic pressure, and plasma beta, among all the 135 HILDCAA* events, found here are: AE (348.1 $\pm$ 67.1 nT), AU (123.9 $\pm$ 34.2 nT), AL (-224.2 $\pm$ 47.3 nT), Dst (-22.1 $\pm$ 9.1 nT), Density (4.3 $\pm$ 1.3 cm-3), Temperature (170976.3 $\pm$ 58049.9 K), Flow speed (547.1 $\pm$ 83.9 km/s), Bz (-0.70 $\pm$ 0.88 nT), IMF magnitude average (6.6 $\pm$ 1.2 nT), pressure (2.4 $\pm$ 0.6 nPa), and plasma Beta (0.66 $\pm$ 0.27).