Properties of the Geomagnetic Storm Main Phase and the Corresponding Solar Wind Parameters on 21–22 October 1999

Abstract

We use the SYM-H index to indicate the ring current index. We find that there were two periods during which the SYM-H index decreased quickly during the main phase of the geomagnetic storm on 21–22 October 1999. The first period from 11:44 p.m. UT on 21 October 1999 to 1:35 a.m. UT on 22 October 1999 is defined as step 1. Another period from 3:36 a.m. UT to 5:49 a.m. UT on 22 October 1999 is defined as step 3. The durations of step 1 and step 3 are defined as Δt1 and Δt3, respectively. The variation of the pressure-corrected SYM-H index during step 1 and step 3 are defined as ΔSYMHob1* and ΔSYMHob3*, respectively. The interplanetary (IP) sources responsible for ΔSYMHob1* and ΔSYMHob3* are determined as the solar wind during period 1 and period 3, respectively. We find that the largest southward component of the interplanetary magnetic field (Bsmax) during period 3 was larger than that during period 1, and the largest solar wind dawn-to-dusk electric field (Eymax) during period 3 was also larger than that during period 1. We also find that the time integral of Ey during period 3 was much larger than that during period 1. However, we find that |ΔSYMHob1*| was larger than |ΔSYMHob3*|, and |ΔSYMHob1*/Δt1| was larger than |ΔSYMHob3*/Δt3|, indicating that the geomagnetic activity intensity during a period does not depend on Bsmax or Eymax, nor does it depend on the time integral of Ey. What is the reason for this? We find that the solar wind dynamic pressure during period 1 was larger than that during period 3, indicating that the geomagnetic storm intensity during a period not only depends on the solar wind speed and Bs, but it also depends on the solar wind dynamic pressure. The magnetosphere took 4 min to respond to the IP shock.When the z-component of the interplanetary magnetic field (IMF) turned from northward to southward, the response time of the SYM-H index to the southward component of the IMF was 21 min.

Properties of the Main Phases of the Super Geomagnetic Storms (ΔSYM-H ≤ −250 nT) with Different Heliolongitudes

“…Therefore, (Wang et al 2003a) showed that the SGS on 2001 March 31 was due to the multiple magnetic clouds, which were formed by the overtaking of successive magnetic clouds. Case studies (Cheng et al 2020;Li et al 2022;Liu et al 2022) found that the solar wind density or dynamic pressure played an important role in the ring current increase speed in the SGS on 2001 March 31 and the great geomagnetic storm on 1999 October 21-22. Statistical studies (Le et al 2020;Zhao et al 2021;Gopalswamy et al 2022;Zhao et al 2022) proved that solar wind dynamic pressure is an important factor for the geomagnetic storm intensity besides the solar wind speed and the southward component (hereafter B s ) of interplanetary magnetic field.…”

“…Hence, only the SYM-H index can describe the rapid variation of the ring current although there is some difference between Dst index and SYM-H index (Katus & Liemohn 2013). It has been proved that the temporal variation of the solar wind parameters correlates well with that of the SYM-H index, but not with that of Dst index (Li et al 2022). The variation of the SYM-H index during the main phase of a geomagnetic storm (hereafter ΔSYM-H) is usually different from the minimum of SYM-H (SYM-H min ).…”

“…Many articles have been devoted to the study of the solar and interplanetary sources for single or many SGSs that occurred during the period from 1957 to the present (e.g., Garcia & Dryer 1987;Allen et al 1989;Cliver & Crooker 1993;Smart & Shea 1996;Huttunen et al 2002;Gopalswamy et al 2005aGopalswamy et al , 2005bGopalswamy et al , 2022Farrugia et al 2005;Jadav et al 2005;Xue et al 2005;Zhang et al 2007;Kataoka & Miyoshi 2008;Cliver et al 2009Cliver et al , 2022Liu et al 2014;Lugaz et al 2015;Lefèvre et al 2016;Vennerstrom et al 2016;Wu et al 2016;Riley et al 2018;Meng et al 2019;Cheng et al 2020;Le & Zhao 2021a;Le et al 2021b;Li et al 2022). Many articles have also been devoted to the estimation of the intensities of geomagnetic storms (e.g., Burton et al 1975;Murayama 1982;Fenrich & Luhmann 1998;O'Brien & McPherron 2000;Temerin & Li 2002;Wang et al 2003b;Tsurutani et al 2003;Kumar et al 2015;Gopalswamy 2018;Zhao et al 2022).…”

A New Index to Describe the Response of Geomagnetic Disturbance to the Energy Injection from the Solar Wind

“…When the IMF is southward, the magnetic reconnection makes the solar wind energy enter the magnetotail region, and when the energy accumulates to a certain extent, the explosive release of particles and energy into the near-Earth space will eventually produce global geomagnetic disturbances. For different physical processes, the time between changes in interplanetary parameters and the response of the magnetosphere will vary, ranging from minutes to days (e.g., [39][40][41][42]). For example, ULF waves in the magnetosphere can be observed at ground-based geomagnetic stations rather quickly after a sudden increase in solar wind dynamic pressure [39], it takes about 30∼60 min for the solar wind energy to be injected into the magnetosphere and accumulated in the magnetotail [43], the formation of global geomagnetic storms will take longer delay time [44].…”

Editorial to the Special Issue “Solar Wind Structures and Phenomena: Origins, Properties, Geoeffectiveness, and Prediction”

“…Rakhmanova et al [10] investigated the transformation of a turbulent cascade behind a quasi-perpendicular bow shock in the magnetosheath depending on the type of large-scale phenomena of solar wind interacting with the Earth's magnetosphere. Li et al [11] analyzed the dynamics of the solar wind that caused a complex, multistep, magnetic storm on 21-22 October 1999.…”