Seasonal and diurnal variation of geomagnetic activity: Russell‐McPherron effect during different IMF polarity and/or extreme solar wind conditions

Abstract

[1] The Russell-McPherron (R-M) effect is one of the most prevailing hypotheses accounting for semiannual variation of geomagnetic activity. To validate the R-M effect and investigate the difference of geomagnetic activity variation under different interplanetary magnetic field (IMF) polarity and during extreme solar wind conditions (interplanetary shock), we have analyzed 42 years interplanetary magnetic field and geomagnetic indices data and 1270 SSC (storm sudden commencement) events from the year 1968 to 2010 by defining the R-M effect with positive/negative IMF polarity (IMF away/toward the Sun). The results obtained in this study have shown that the response of geomagnetic activity to the R-M effect with positive/negative IMF polarity are rather profound: the geomagnetic activity is much more intense around fall equinox when the direction of IMF is away the Sun, while much more intense around spring equinox when the direction of IMF is toward the Sun. The seasonal and diurnal variation of geomagnetic activity after SSCs can be attributed to both R-M effect and the equinoctial hypothesis; the R-M effect explains most part of variance of southward IMF, while the equinoctial hypothesis explains similar variance of ring current injection and geomagnetic indices as the R-M effect. However, the R-M effect with positive/negative IMF polarity explains the difference between SSCs with positive/negative IMF B y accurately, while the equinoctial hypothesis cannot explain such difference at the spring and fall equinoxes. Thus, the R-M effect with positive/negative IMF polarity is more reasonable to explain seasonal and diurnal variation of geomagnetic activity under extreme solar wind conditions. Citation: Zhao, H., and Q.-G. Zong (2012), Seasonal and diurnal variation of geomagnetic activity: Russell-McPherron effect during different IMF polarity and/or extreme solar wind conditions,

On the origins and timescales of geoeffective IMF

“…The < Dst > values are all negative and reveal unambiguously the R‐M effect with larger disturbances near the March/September equinoxes when the prior IMF B Y (GSE) has been predominantly negative/positive, respectively. As noted by Zhao and Zong [], this is a unique signature of the R‐M effect. The number of storm hours with Dst o < Dst o (for which values are always positive) does show this effect, but it is much less pronounced.…”

“…Russell and McPherron [] argued that the R‐M effect was the cause of the enhanced occurrence of large geomagnetic storms at the equinoxes. A key test of the idea that the R‐M effect is central to any semiannual variation was made by Zhao and Zong []. These authors showed that which of the two equinoxes was favored in generating geomagnetic activity depended on the polarity of the IMF B Y (GSE) component.…”

D‐Region High‐Latitude Forcing Factors

“…The daytime and nighttime SAO relation to geomagnetic activity and particle fluxes could be explained by the semiannual variation in geomagnetic activity (Svalgaard, ). Using Figure of Zhao and Zong (), and according to the method we use to differentiate between daytime and nighttime variability, we can apply the Russell‐McPherron effect (Russell & McPherron, ) and the equinoctial hypothesis, respectively, to explain the SAO observed in the VLF amplitude variations. The main difference between these two semiannual variations is that the equinoctial hypothesis is related to modulation of the existing geomagnetic activity, while the Russell‐McPherron effect is producing the geomagnetic activity (Svalgaard, ).…”

The Intense Substorm Incidence in Response to Interplanetary Shock Impacts and Influence on Energetic Electron Fluxes at Geosynchronous Orbit

“…This effect is called “Russel‐McPherron effect” (R‐M effect). This effect is a coupling effect between Geocentric Solar Magnetospheric (GSM) coordinate system and Geocentric Solar Equatorial (GSE) coordinate system causing the average IMF oriented at the Parker spiral angle project a southward component at Earth (Zhao & Zong, ). Therefore, at the Spring equinox the negative B y in GSE coordinates can provide a maximum southward Bz in the GSM coordinates, and at the Autumn equinox the positive B y in GSE coordinates can provide a maximum southward Bz in the GSM coordinates.…”