![]() ![]() The âD variations clearly showed seasonal asymmetry in the dawn and noon sectors, whereas the âD variations in the dusk sector demonstrated seasonal symmetry. The dusk-side IHFACs around March and September-November months disagreed with the Fukushima model. It was confirmed that the dusk-side IHFACs during June and December solstices flow in the same direction of the noontime IHFACs, which was consistent with the IHFAC polarities suggested by the Fukushima model. We investigated the consistency of the dusk-side IHFAC polarity derived from the observations with the polarity expected from Fukushima's IHFACs model and examined the solar cycle dependence of IHFACs. Recent in situ satellite and ground-based observations have reported that dusk-side current polarity of IHFAC is often opposite to that of the noon IHFAC, being inconsistent with Fukushima's IHFACs model. Journal of Geophysical Research: Space Physics Wiley The east-west component of magnetic field variation (âD-component) at Davao station (Philippines, geomagnetic latitude: - 2.22°N) are used to investigate the characteristics of the long-term Inter-Hemispheric Field-Aligned Currents (IHFACs) based on the time-series analysis from August 1998 to July 2020. It is concluded that southward directed interplanetary magnetic fields within CIRs/HSSs may be the main energy source for long‐term averaged geomagnetic activity on Earth. It was found that ~80.1% of the storms follow the criterion of Ey ≥ 2 mV m−1 for intervals longer than 2 h. The typical interplanetary electric field (Ey) criteria for moderate magnetic storms were identified. CIRs caused only 13% of the intense storms. For superintense geomagnetic storms, 100% of the events were due to ICME events, while for intense storms, ICMEs, sheaths, and their combination caused almost 80% of the storms. This result is significantly different than that for intense (Dst ≤ −100 nT) and superintense (Dst ≤ −250 nT) magnetic storms shown in previous studies. #Omniweb nasa dst index driverThus, CIRs and HSSs are the main driver of moderate storms throughout a solar cycle but with variable contributions from ICMEs, their shocks (sheaths), and combined occurrence within the solar cycle. #Omniweb nasa dst index plusCIRs and HSSs combined have about the same level of importance as ICMEs plus their sheaths in the rising and maximum solar cycle phases. #Omniweb nasa dst index driversIn terms of solar cycle dependence, CIRs and HSSs are the dominant drivers in the declining phase and at solar minimum. Most of these storms were associated with CIRs and pure HSSs (47.9%), followed by MCs and noncloud ICMEs (20.6%), pure sheath fields (10.8%), and sheath and ICME combined occurrence (9.9%). All moderate‐intensity storms were associated with southward interplanetary magnetic fields, indicating that magnetic reconnection was the main mechanism for solar wind energy transfer to the magnetosphere. The lowest occurrence rate was 5.7 storms year−1 and occurred at solar minimum. The highest rate of moderate storm occurrence was found in the declining phase (25 storms year−1). The annual rate of occurrence of moderate storms had two peaks, one near solar maximum and the other in the descending phase, around 3 years later. Interplanetary drivers such as corotating interaction regions (CIRs), pure high‐speed streams (HSSs), interplanetary coronal mass ejections (ICMEs) of two types, sheaths (compressed and/or draped sheath fields), as well as their combined occurrence were identified as causes of the storms. The interplanetary causes of 213 moderate‐intensity (−100 nT < peak Dst ≤ −50 nT) geomagnetic storms that occurred in solar cycle 23 (1996–2008) are identified. ![]() Interplanetary origins of moderate (−100 nT < Dst ≤ −50 nT) geomagnetic storms during solar cycle 23 (1996–2008) Interplanetary origins of moderate (−100 nT < Dst ≤ −50 nT) geomagnetic storms during solar cycle.Įcher, E. ![]()
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