Solar Wind Low-Temperature Periods and Forbush Decreases: a Statistical Comparison

Abstract

Based on a large amount of experimental material, the hourly values of the solar wind speed and proton temperature were compared; the expected proton temperature and temperature index (the ratio of the observed temperature to the expected one) were calculated. Using the Cosmic Ray Variations Database, from 1997 to 2022 low-temperature periods were identified (intervals lasting more 2 h, in which hourly values of the temperature index less than 0.5). The study investigated (a) statistical relationships between the parameters of low-temperature periods and the characteristics of Forbush decreases associated with different types of solar sources; (b) distributions of parameters of low-temperature periods for interplanetary disturbances containing or not containing a magnetic cloud. The results showed that with increasing duration of the low-temperature period, the proportion of events associated with ejections from active regions increases, while the proportion of recurrent events and events associated with ejections outside active regions decreases. The correlation of the parameters of low-temperature periods with the magnitude of Forbush decreases is weak; with the equatorial anisotropy of cosmic rays, moderate; and with the azimuthal anisotropy, significant. The solar wind speed and magnetic field strength correlate moderately with the temperature index, and the correlation of the range of these parameters with the duration of low-temperature periods is significant or strong.