Severe geomagnetic storms and Forbush decreases: interplanetary relationships reexamined

Abstract

Abstract. Severe storms (Dst) and Forbush decreases (FD) during cycle 23 showed that maximum negative Dst magnitudes usually occurred almost simultaneously with the maximum negative values of the B z component of interplanetary magnetic field B, but the maximum magnitudes of negative Dst and B z were poorly correlated (+0.28). A parameter B z (CP) was calculated (cumulative partial B z ) as sum of the hourly negative values of B z from the time of start to the maximum negative value. The correlation of negative Dst maximum with B z (CP) was higher (+0.59) as compared to that of Dst with B z alone (+0.28). When the product of B z with the solar wind speed V (at the hour of negative B z maximum) was considered, the correlation of negative Dst maximum with V B z was +0.59 and with V B z (CP), 0.71. Thus, including V improved the correlations. However, ground-based Dst values have a considerable contribution from magnetopause currents (several tens of nT, even exceeding 100 nT in very severe storms). When their contribution is subtracted from Dst(nT), the residue Dst* representing true ring current effect is much better correlated with B z and B z (CP), but not with V B z or V B z (CP), indicating that these are unimportant parameters and the effect of V is seen only through the solar wind ram pressure causing magnetopause currents. Maximum negative Dst (or Dst*) did not occur at the same hour as maximum FD. The time evolutions of Dst and FD were very different. The correlations were almost zero. Basically, negative Dst (or Dst*) and FDs are uncorrelated, indicating altogether different mechanism.

How are Forbush decreases related to interplanetary magnetic field enhancements?

“…Belov et al (2001) and Kane (2010) maintain that there is a reasonable correlation between the FD magnitude and the product of maximum magnetic field and maximum solar wind velocity. Dumbović et al (2012) also found reasonable correlation A&A 580, A41 (2015) detectors (each 1 m 2 ), with a distance of 8 m between adjacent detectors deployed in a hexagonal geometry (Gupta et al 2005;Mohanty et al 2009;Mohanty et al 2012).…”

Variability of Low Energy Cosmic Rays Near Earth

“…Thus the interest to the measurements of positrons and antiprotons is increasing. Important finding was done by PAMELA experiment (Adriani et al, 2009;2010). The authors present data on the positron abundance in the CR in the energy range 1.5 -100 GeV with high statistics.…”

“…Mustajab and Badruddin (2011) critically analyze the differences in geoeffectiveness due to different structures and features, with distinct plasma/field characteristics. Distinct relations of FDs and geomagnetic activity measured by Dst in different events is reported by (Kudela and Brenkus, 2004;Kane, 2010). Richardson and Cane (2011) analyzed large number of ICMEs and their associated shocks passing the Earth during years 1995 -2009.…”

“…Progress in clarifying mechanisms controlling the secondary CR flux required the design and construction of new detectors. Production of secondary CRs is reviewed in the books (Grieder, 2001;2010). Until half of the past century the elementary particle physics was driven mainly by CR studies.…”

Galactic cosmic-ray energy spectra and expected solar events at the time of future space missions

“…The sporadic Forbush decreases of the GCR intensity are associated with major solar flares. These Forbush decreases can be caused by (1) shock and ejecta, (2) shock only or (3) ejecta only [33]. Sporadic Forbush decreases generate drops of the order of 5-10% at 10 GV rigidity.…”