ИСТИНА

Original ULF index was suggested (Kozyreva et al., 2007) for Pc5 frequency range and verified for auriral latitudes in the Northern hemisphere. Typical for polar caps ULF are broadband and theit frequencies are somewhat lower (1-4 mHz), than for classical auroral Pc5s. They are denoted as Pi3cap pulsation (Yagova et al., 2004). Their spectral parameters depend on magnetic local time and latitude and they can demonstrate a precursor behavior before substorms without evident external trigger (Yagova et al., 2010, 2017). However, Pi3 properties in polar caps under different space weather conditions are not known in details. The present study is aimed on systematic study of Pi3 polar cap properties in dependence of space weather conditions. For that, the ULF index is modified for the southern hemisphere. The behavior of the index under different variants of boundaries in magnetic latitudes and MLT is studied and an optimal choice is found. Spectral slope, quality factor, and higher moments of spectral distribution of polar cap Pi3s in two hemispheres are analyzed for different space weather conditions. This study is supported by the RFBR grant # 20-05-00787