Effects of IMF By on Ring Current Asymmetry Under Southward IMF Bz Conditions Observed at Ground Magnetic Stations: Case Studies

Abstract

In this paper, we have evaluated the role of interplanetary magnetic field (IMF) By on the asymmetry of the ring current during the main phase of geomagnetic storms. The mean H variations have been calculated using 31 ground magnetic stations over magnetic latitudes of 09-45°following the methodology of Li et al. (2011, https://doi.org/10.1029/2011JA016886). Further, the magnetic local time (MLT) variations in the H component at these stations w.r.t. the mean H were investigated for three cases of geomagnetic storms with varying southward IMF Bz and IMF By conditions. Significant ring current asymmetries were observed during the main phase of geomagnetic storms. The primary role of IMF Bz on the asymmetry of the ring current is observed from these cases. More importantly, the investigation brings out for the first time, the additional role of IMF By in influencing the MLT distribution of ring current observed at ground magnetic stations. Under southward IMF Bz conditions, it is shown based on SuperDARN and AMPERE data that IMF By can alter the MLT distribution of ring current under suitable conditions. The timescales of IMF By also play very important role in determining the asymmetry in the ring current. Under steady convection state, IMF By can rotate the convection cells based on its polarity, which in turn can change the MLT distribution of ring current observed by low-latitude ground stations. This investigation, thus, brings out the important role of IMF By on the asymmetric MLT distribution of ring current under southward IMF Bz.

Origin of Dawnside Subauroral Polarization Streams During Major Geomagnetic Storms

“…IMF B Y increased to a maximum of positive 40 nT at around 12 UT during the early main phase. A strong IMF B Y is known to cause a substantial dawn‐dusk asymmetry of the coupled magnetosphere‐ionosphere (e.g., Holappa et al., 2020; Kumar et al., 2020; Shepherd & Ruohoniemi, 2000). We conducted another controlled experiment using a MAGE simulation in which IMF B Y was artificially reduced to zero, while other solar wind and IMF parameters were the observed values, which are shown in Figure S12 in Supporting Information .…”

Contribution of Electron Pressure to Ring Current and Ground Magnetic Depression Using RAM‐SCB Simulations and Arase Observations During 7–8 November 2017 Magnetic Storm

“…In order to see the ring current asymmetry, the mean Δ H m (from Equation ) is subtracted from the Δ H of each station to calculate Δ H asy (Δ H asy = Δ H −Δ H m ) (Kumar et al., 2020). The top panel of Figure 7 shows the variation of Δ H asy with 1‐min resolution with UT ( X ‐axis) and MLT ( Y ‐axis) along with pressure corrected Sym‐ H (Sym‐ H *) during 7–8 November 2017.…”

“…The global ground geomagnetic field depression during geomagnetic storms is caused by the ring current. It is well known that the ring current is highly asymmetric during main and early recovery phase during geomagnetic storms and dawn-dusk asymmetry is observed (Ebihara & Ejiri, 2000;Fok et al, 1996;Jordanova et al, 2006;Kumar et al, 2020;Liemohn et al, 1999;Sugiura & Chapman, 1960). In the present study, we compared the ion and electron fluxes calculated with RAM-SCB with Arase observations.…”

“…The mean variation ΔH m is calculated using a method described by Li et al (2011) and Kumar et al, (2020).…”

“…The mean variation Δ H m is calculated using a method described by Li et al. (2011) and Kumar et al., (2020). where Δ H is calculated from Equation and N is the total number of stations.…”