Drop of Solar Wind at the End of the 20th Century

Abstract

Variations in the solar wind (SW) parameters with scales of several years are an important characteristic of solar activity and the basis for a long‐term space weather forecast. We examine the behavior of interplanetary parameters over 21–24 solar cycles (SCs) on the basis of the OMNI database (https://spdf.gsfc.nasa.gov/pub/data/omni). Since changes in the parameters can be associated with both changes in the number of different large‐scale types of SW and with variations in the values of these parameters at different phases of the solar cycle and during the transition from one cycle to another, we select the entire study period in accordance with the Catalog of large‐scale SW types for 1976–2019 (see the site http://www.iki.rssi.ru/pub/omni, [Yermolaev, Nikolaeva, et al., 2009, https://doi.org/10.1134/s0010952509020014], which covers the period from 21 to 24 SCs) and in accordance with the phases of the cycles, and average the parameters at selected intervals. In addition to a sharp drop in the number of interplanetary coronal mass ejections and associated sheath types, there is a noticeable drop in the value (by 20%–40%) of plasma parameters and magnetic field in different types of solar wind at the end of the 20th century and a continuation of the fall or persistence at a low level in the 23–24 cycles. Such a drop in the solar wind is apparently associated with a decrease in solar activity and manifests itself in a noticeable decrease in space weather factors.

“Obstanovka” experiment on determining spacecraft surface charging aboard the International Space Station

“…As a result of this analysis, the following important conclusion can be drawn. In addition to the well-known fact that in 23-24 solar cycles the number of disturbed types of solar wind (ICME and related Sheath types) sharply decreased, at the end of the 20th century and the beginning of the 21st century there is a noticeable drop (by 20-40%) in the values of the parameters plasma and magnetic field in various types of solar wind and the low level of parameters persists or continues to decrease in 23-24 cycles [Yermolaev et al, 2021].…”

Solar activity and space weather

“…The geoeffectiveness of SC 24 MCs relative to the ones in SC 23 declined by 49%; the geoeffectiveness of sheaths ahead of MCs declined by 59% [23]. Yermolaev et al [30] showed the reduced geoeffectiveness to be similar in non-cloud ejecta and sheath. In addition, these authors compared the geoeffectiveness of various solar wind structures that occurred in SCs 21-24 and found drastic reduction of geoeffectiveness in SC 24 compared to that in other cycles.…”

“…The altered properties of CMEs resulted space weather that is milder than what is expected from the reduced activity alone. The same applies to space weather caused by CIRs [4,29,30]. Instead of looking at the intense geomagnetic storms, if one starts with the magnetic clouds (MCs) and examines their space weather impact, the reduction in geoeffectiveness (as measured by Dst) is again clear [23,30].…”

“…The same applies to space weather caused by CIRs [4,29,30]. Instead of looking at the intense geomagnetic storms, if one starts with the magnetic clouds (MCs) and examines their space weather impact, the reduction in geoeffectiveness (as measured by Dst) is again clear [23,30]. The geoeffectiveness of SC 24 MCs relative to the ones in SC 23 declined by 49%; the geoeffectiveness of sheaths ahead of MCs declined by 59% [23].…”

Gleissberg Cycle Dependence of Inner Zone Proton Flux

“…This longer term data set allows us to investigate the Gleissberg cycle variation of inner belt protons (Feynman & Ruzmaikin, 2011;Gleissberg, 1944;Pulkkinen et al, 2001;Svalgaard et al, 2005). Feynman and Ruzmaikin (2011) described the Centennial Gleissberg Cycle as an approximately century-long sinusoidal variation in the intensity of solar maximum well established in sunspot number, finding evidence to suggest that Solar Cycles 23 and 24 represent a minimum of this 80 to 100-year cycle (Yermolaev et al, 2021) which follows the higher activity level of the early space age going back to the 1960 solar maximum. Several studies predict a weak solar maximum for Solar Cycle 25 (c.g.…”