I. G. Lodkina

Catalog of Large-Scale Solar Wind Phenomena during 1976-2000

The main goal of this paper is to compile a catalog of large-scale phenomena in the solar wind over the observation period of 1976–2000 using the measurement data presented in the OMNI database. This work included several stages. At first the original OMNI database was supplemented by certain key parameters of the solar wind that determine the type of the solar wind stream. The following parameters belong to this group: the plasma ratio β, thermal (NkT) and kinetic (mNV2) pressures of the solar wind, the ratio T/Texp of measured and expected temperatures, gradients of the plasma velocity and density, and the magnetic field gradient. The results of visualization of basic plasma parameters that determine the character of the solar wind stream are presented on the website of the Space Research Institute, Moscow. Preliminary identification of basic types of the solar wind stream (FAST and SLOW streams, Heliospheric Current Sheet (HCS), Corotating Interaction Region (CIR), EJECTA (or Interplanetary Coronal Mass Ejections), Magnetic Cloud (MC), SHEATH (compression region before EJECTA/MC), rarified region RARE, and interplanetary shock wave IS) had been made with the help of a preliminary identification program using the preset threshold criteria for plasma and interplanetary magnetic field parameters. Final identification was done by comparison with the results of visual analysis of the solar wind data. In conclusion, histograms of distributions and statistical characteristics are presented for some parameters of various large-scale types of the solar wind.

Geoeffectiveness and efficiency of CIR, sheath, and ICME in generation of magnetic storms

We investigate relative role of various types of solar wind streams in generation of magnetic storms. On the basis of the OMNI data of interplanetary measurements for the period of 1976-2000 we analyze 798 geomagnetic storms with Dst < -50 nT and their interplanetary sources: corotating interaction regions (CIR), interplanetary CME (ICME) including magnetic clouds (MC) and Ejecta and compression regions Sheath before both types of ICME. For various types of solar wind we study following relative characteristics: occurrence rate; mass, momentum, energy and magnetic fluxes; probability of generation of magnetic storm (geoeffectiveness) and efficiency of process of this generation. Obtained results show that despite magnetic clouds have lower occurrence rate and lower efficiency than CIR and Sheath they play an essential role in generation of magnetic storms due to higher geoeffectiveness of storm generation (i.e higher probability to contain large and long-term southward IMF Bz component).

Statistical Investigation of Heliospheric Conditions Resulting in Magnetic Storms: 2

Time behavior of the solar wind and interplanetary magnetic field parameters is investigated for 623 magnetic storms of the OMNI database for the period 1976–2000. The analysis is carried out by the superposed epoch technique (the magnetic storm onset time is taken to be the beginning of an epoch) for five various categories of storms induced by various types of solar wind: CIR (121 storms), Sheath (22 storms), MC (113 storms), and “uncertain type” (367 storms). In total, the analysis conducted for “all storms” included 623 storms. The obtained data, on one hand, confirm the results obtained earlier without selecting the intervals according to the solar wind types, and, on the other hand, they indicate the existence of distinctions in the time variation of parameters for various types of solar wind. Though the lowest values of the Bz-component of IMF are observed in the MC, the lowest values of the Dst-index are achieved in the Sheath. Thus, the strongest magnetic storms are induced, on average, during the Sheath rather than during the MC body passage, probably owing to higher pressure in the Sheath. Higher values of nkT, T/Texp, and β parameters are observed in the CIR and Sheath and lower ones in the MC, which corresponds to the physical essence of these solar wind types.

Dependence of Geomagnetic Activity during Magnetic Storms on the Solar Wind Parameters for Different Types of Streams

The dependence of the maximal values of the |Dst| and AE geomagnetic indices observed during magnetic storms on the value of the interplanetary electric field (Ey) was studied based on the catalog of the large-scale solar wind types created using the OMNI database for 1976–2000 [Yermolaev et al., 2009]. An analysis was performed for eight categories of magnetic storms caused by different types of solar wind streams: corotating interaction regions (CIR, 86 storms); magnetic clouds (MC, 43); Sheath before MCs (ShMC, 8); Ejecta (95); Sheath (ShE, 56); all ICME events (MC + Ejecta, 138); all compression regions Sheaths before MCs and Ejecta (ShMC + ShE, 64); and an indeterminate type of storm (IND, 75). It was shown that the |Dst| index value increases with increasing electric field Ey for all eight types of streams. When electric fields are strong (Ey > 11 mV m−1), the |Dst| index value becomes saturated within magnetic clouds MCs and possibly within all ICMEs (MC + Ejecta). The AE index value during magnetic storms is independent of the electric field value Ey for almost all streams except magnetic clouds MCs and possibly the compressed (Sheath) region before them (ShMC). The AE index linearly increases within MC at small values of the electric field (Ey < 11 mV m−1) and decrease when these fields are strong (Ey > 11 mV m−1). Since the dynamic pressure (Pd) and IMF fluctuations (σB) correlate with the Ey value in all solar wind types, both geomagnetic indices (|Dst| and AE) do not show an additional dependence on Pd and IMF δB. The nonlinear relationship between the intensities of the |Dst| and AE indices and the electric field Ey component, observed within MCs and possibly all ICMEs during strong electric fields Ey, agrees with modeling the magnetospheric-ionospheric current system of zone 1 under the conditions of the polar cap potential saturation.

Relative occurrence rate and geoeffectiveness of large-scale types of the solar wind

We investigate the relative occurrence rate for various types of the solar wind and their geoeffectiveness for magnetic storms with Dst < —50 nT. Both integrated effect for the entire time 1976–2000 and variations during this period of 2.5 cycles of solar activity are studied As raw data for the analysis we have used the catalog of large-scale types of the solar wind for the period 1976-2000 (see ftp://ftp.iki.rssi.ru/omni/) created by us with the use of the OMNI database (http://omni.web.gsgc.nasa.gov) [1] and described in detail in [2]. The average annual numbers of different type of events are as follows: 124 ±81 for the heliospheric current sheet (HCS), 8 ±6 for magnetic clouds (MC), 99 ±38 for Ejecta, 46 ±19 for Sheath before Ejecta, 6 ±5 for Sheath before MC, and 63 ±15 for CIR. The measurements that allowed one to determine a source in the solar wind were available only for 58% of moderate and strong magnetic storms (with index Dst < —50 nT) during the period 1976–2000. Magnetic clouds (MC) are shown to be the most geoeffective (~61%). The CIR events and Ejecta with Sheath region are three times less geoeffective (~20–21 %). Variations of occurrence rate and geoeffectiveness of various types of the solar wind in the solar cycle are discussed.

Dynamics of large‐scale solar wind streams obtained by the double superposed epoch analysis

Using the OMNI data for period 1976–2000, we investigate the temporal profiles of 20 plasma and field parameters in the disturbed large-scale types of solar wind (SW): corotating interaction regions (CIR), interplanetary coronal mass ejections (ICME) (both magnetic cloud (MC) and Ejecta), and Sheath as well as the interplanetary shock (IS). To take into account the different durations of SW types, we use the double superposed epoch analysis (DSEA) method: rescaling the duration of the interval for all types in such a manner that, respectively, beginning and end for all intervals of selected type coincide. As the analyzed SW types can interact with each other and change parameters as a result of such interaction, we investigate separately eights sequences of SW types: (1) CIR, (2) IS/CIR, (3) Ejecta, (4) Sheath/Ejecta, (5) IS/Sheath/Ejecta, (6) MC, (7) Sheath/MC, and (8) IS/Sheath/MC. The main conclusion is that the behavior of parameters in Sheath and in CIR are very similar both qualitatively and quantitatively. Both the high-speed stream (HSS) and the fast ICME play a role of pistons which push the plasma located ahead them. The increase of speed in HSS and ICME leads at first to formation of compression regions (CIR and Sheath, respectively) and then to IS. The occurrence of compression regions and IS increases the probability of growth of magnetospheric activity.

Statistical study of interplanetary condition effect on geomagnetic storms

Based on the archive OMNI data for the period 1976–2000 an analysis has been made of 798 geomagnetic storms with Dst < −50 nT and their interplanetary sources-large-scale types of the solar wind: CIR (145 magnetic storms), Sheath (96), magnetic clouds MC (62), and Ejecta (161). The remaining 334 magnetic storms have no well-defined sources. For the analysis, we applied the double method of superposed epoch analysis in which the instants of the magnetic storm beginning and minimum of Dst index are taken as reference times. The well-known fact that, independent of the interplanetary source type, the magnetic storm begins in 1–2 h after a southward turn of the IMF (Bz < 0) and both the end of the main phase of a storm and the beginning of its recovery phase are observed in 1–2 h after disappearance of the southward component of the IMF is confirmed. Also confirmed is the result obtained previously that the most efficient generation of magnetic storms is observed for Sheath before MC. On the average parameters Bz and Ey slightly vary between the beginning and end of the main phase of storms (minimum of Dst and Dst* indices), while Dst and Dst* indices decrease monotonically proportionally to integral of Bz and Ey over time. Such a behavior of the indices indicates that the used double method of superposed epoch analysis can be successfully applied in order to study dynamics of the parameters on the main phase of magnetic storms having different duration.

Modeling the Time Behavior of the D st Index during the Main Phase of Magnetic Storms Generated by Various Types of Solar Wind

Results of modeling the time behavior of the Dst index at the main phase of 93 geomagnetic storms (−250 < Dst ≤ −50 nT) caused by different types of solar wind (SW) streams: magnetic clouds (MC, 10 storms), corotating interaction regions (CIR, 31 storms), the compression region before interplanetary coronal ejections (Sheath before ICME, 21 storms), and “pistons” (Ejecta, 31 storms) are presented. The “Catalog of Large-Scale Solar Wind Phenomena during 1976–2000” (ftp://ftp.iki.rssi.ru/pub/omni/) created on the basis of the OMNI database was the initial data for the analysis. The main phase of magnetic storms is approximated by a linear dependence on the main parameters of the solar wind: integral electric field sumEy, dynamic pressure Pd, and fluctuation level sB in IMF. For all types of SW, the main phase of magnetic storms is better modeled by individual values of the approximation coefficients: the correlation coefficient is high and the standard deviation between the modeled and measured values of Dst is low. The accuracy of the model in question is higher for storms from MC and is lower by a factor of ∼2 for the storms from other types of SW. The version of the model with the approximation coefficients averaged over SW type describes worse variations of the measured Dst index: the correlation coefficient is the lowest for the storms caused by MC and the highest for the Sheath- and CIR-induced storms. The model accuracy is the highest for the storms caused by Ejecta and, for the storms caused by Sheath, is a factor of ∼1.42 lower. Addition of corrections for the prehistory of the development of the beginning of the main phase of the magnetic storm improves modeling parameters for all types of interplanetary sources of storms: the correlation coefficient varies within the range from r = 0.81 for the storms caused by Ejecta to r = 0.85 for the storms caused by Sheath. The highest accuracy is for the storms caused by MC. It is, by a factor of ∼1.5, lower for the Sheath-induced storms.

Statistical study of interplanetary condition effect on geomagnetic storms: 2. Variations of parameters

We investigate the behavior of mean values of the solar wind’s and interplanetary magnetic field’s (IMF) parameters and their absolute and relative variations during the magnetic storms generated by various types of the solar wind. In this paper, which is a continuation of paper [1], we, on the basis of the OMNI data archive for the period of 1976–2000, have analyzed 798 geomagnetic storms with Dst ≤ −50 nT and their interplanetary sources: corotating interaction regions CIR, compression regions Sheath before the interplanetary CMEs; magnetic clouds MC; “Pistons” Ejecta, and an uncertain type of a source. For the analysis the double superposed epoch analysis method was used, in which the instants of the magnetic storm onset and the minimum of the Dst index were taken as reference times. It is shown that the set of interplanetary sources of magnetic storms can be sub-divided into two basic groups according to their slowly and fast varying characteristics: (1) ICME (MC and Ejecta) and (2) CIR and Sheath. The mean values, the absolute and relative variations in MC and Ejecta for all parameters appeared to be either mean or lower than the mean value (the mean values of the electric field Ey and of the Bz component of IMF are higher in absolute value), while in CIR and Sheath they are higher than the mean value. High values of the relative density variation sN/〈N〉 are observed in MC. At the same time, the high values for relative variations of the velocity, Bz component, and IMF magnitude are observed in Sheath and CIR. No noticeable distinctions in the relationships between considered parameters for moderate and strong magnetic storms were observed.

Influence of the interplanetary driver type on the durations of the main and recovery phases of magnetic storms

We study the durations of the main and recovery phases of magnetic storms induced by different types of large-scale solar-wind streams (Sheath, magnetic cloud (MC), Ejecta, and corotating interaction region (CIR)) on the basis of OMNI data for 1976–2000. The durations of both the main and recovery phases depend on the type of interplanetary drivers. On average, the duration of the main phase of storms induced by compressed regions (CIR and Sheath) is shorter than for MC and Ejecta, while the duration of the recovery phase of CIR- and Sheath-induced storms is longer. Analysis of the durations of individual storms shows that the durations of the main and recovery phases anticorrelate for CIR- and Sheath-induced storms and there is no dependence between them for (MC + Ejecta)-induced storms.