On the variation of small-amplitude Forbush decreaseswith solar-geomagnetic parameters

Résumé

Abstract Detection of weak signals remains challeng-ing in astrophysics. This is particularly applicable inthe investigation of Forbush events. There is thus,a paucity of catalogs of small-amplitude Forbush de-creases (FDs). Detail investigations of the space-weather implications of small FDs are, thus, lacking inthe literature. Recently, large catalogs of weak FDs, forthe first time, have been published. This work employsthe newly created lists of small-amplitude FDs to inves-tigate the statistical link between small FDs and solar-geomagnetic variables. The solar-geomagnetic variableswere obtained from the OMNI database. A simple co-incident R software code was employed in matchingthe related solar-geomagnetic variables with the weakForbush events. The FD dates were taken as the inputsignal. Scatter plots of FD-IMF, FD-SWS, FD-Kp, FD-Ap reveal a negative relationship, while that of FD-Dstshows a positive relationship. Statistical significanceof these relations were tested. The small-amplitudeFDs and solar-geomagnetic variables at Potchefstroom(PTFM) station register statistically significant rela-tions. Non-statistically significant correlation betweenthe small-amplitude FDs and solar-geomagnetic vari-ables were obtained at South Pole (SOPO) station, withthe exception of FD-SWS that reveals statistically sig-nificant correlation. The differences in the correlationresults obtained at the two stations (PTFM and SOPO)could be attributed to the differences in the character-istics of the NM stations. These results suggest that geomagnetic storm indices play important role in theevolution of FDs.

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