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In this work, the relation between Dst* (solar wind pressure corrected Dst) and solar wind parameters (north–south component of the interplanetary magnetic field B z and east–west component of the electric field E y) in the main phase of the single-step geomagnetic storms was analyzed on their peak (Dst* p and B zp / E yp) and difference values (ΔDst* p and ΔB z /ΔE y). From 1995 to 2019, 133 storms with peak Dst * ≤ −50 nT were selected. It was found that the correlations between Dst* p and B zp / E yp (r = 0.60 and −0.69) were higher than those between Dst* p and ΔB z /ΔE y (r = −0.49 and −0.45, respectively). The correlation between the variations of ΔDst* and ΔB z / ΔE y were intermediate between those ranges (r = 0.52 and 0.45, respectively). Multiple linear correlation of Dst* p with B zp /ΔB z and E yp / ΔE y explains 38 and 48% of the variance of Dst* p , respectively, with a larger effect of peak values of solar wind parameters. There were twice more single-step storms in cycle 23 than in cycle 24, but the average values of peaks and variations did not show significant differences. In terms of E yp criteria for moderate (−100 nT < Dst* p ≤ −50 nT) and intense (Dst* p ≤ 100 nT) geomagnetic storms, >93% of the moderate storms had E yp > 3 mV·m−1, while 96% of intense storms had E yp > 5 mV·m−1. On ΔE y , 87% of the moderate storms had ΔE y ≤ 10 mV·m−1, while 72% of the intense storms had ΔE y > 10 mV·m−1. Thus it may be concluded that B zp and E yp were important for Dst* p of the single-step storms and that E yp and Δ E y values could be interplanetary criteria for the moderate and intense storms. [ABSTRACT FROM AUTHOR]

Abstract: A catalog of 1377 geomagnetic storms with peak Dst (Dst p )≤−50nT for the period 1957–2008 has been compiled. The dependence of Dst p on the solar cycle and annual variation are studied in this paper. It is found that geomagnetic storm peak intensity distribution can be described by an exponential form, , where P is the probability of geomagnetic storm occurrence with a given value Dst p . The updated solar cycle and annual distribution of geomagnetic storms have confirmed the expected behavior. For the solar cycle variation, geomagnetic storms display a two-peak distribution, with one peak close to solar maximum and the other a few years later in the beginning of the declining phase. Geomagnetic storms follow the well-known seasonal variation of geomagnetic activity. More intense storms show a peak in probability occurrence in July, confirming previous observations. These results are of practical importance for space weather applications. [Copyright &y& Elsevier]

Abstract: The sun was very active in the declining phase of solar cycle 23. Large sunspot active regions gave origin to multiple flare and coronal mass ejection (CME) activity in the interval 2003–2005. On November 2004, the active region AR 10696 was the origin of dozens of flares and many CMEs. Some events of this solar activity region resulted in two large geomagnetic storms, or superstorms (Dst⩽−250nT) on November 8, peak Dst=−373nT, and on November 10, peak Dst=−289nT. It is the purpose of this article to identify the interplanetary origins of these two superstorms. The southward-directed interplanetary magnetic fields (IMF Bs) that caused the two superstorms were related to a magnetic cloud (MC) field for the first superstorm, and a combination of sheath and MC fields for the second superstorm. However, this simple, classic picture is complicated by the presence of multiple shocks and waves. Six fast-forward shocks and, at least, two reverse waves were observed in the period of the two superstorms. A detailed analysis of these complex interplanetary features is performed in this work. [Copyright &y& Elsevier]

Abstract: Plasma and magnetic field parameter variations through fast forward interplanetary shocks were correlated with the peak geomagnetic activity index Dst in a period from 0 to 3 days after the shock, during solar maximum (2000) and solar minimum (1995–1996). Solar wind speed (V) and total magnetic field (B t) were the parameters with higher correlations with peak Dst index. The correlation coefficients were higher during solar minimum (r 2 =56% for V and 39% for B t) than during solar maximum (r 2 =15% for V and 12% for B t). A statistical distribution of geomagnetic activity levels following interplanetary shocks was obtained. It was observed that during solar maximum, 36% and 28% of interplanetary shocks were followed by intense (Dst⩽−100nT) and moderate (−50⩽Dst<−100nT) geomagnetic activity, whereas during solar minimum 13% and 33% of the shocks were followed by intense and moderate geomagnetic activity. It can be concluded that the upstream/downstream variations of V and B t through the shocks were the parameters better correlated with geomagnetic activity level, and during solar maximum a higher relative number of interplanetary shocks can be followed by intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar cycle a shock has a probability of around 50% to be followed by intense/moderate geomagnetic activity. [Copyright &y& Elsevier]

Abstract: In this work a study is performed on the correlation between fast forward interplanetary shock parameters at 1 Astronomical Unit and sudden impulse (SI) amplitudes in the H-component of the geomagnetic field, for periods of solar activity maximum (year 2000) and minimum (year 1995–1996). Solar wind temperature, density and speed, and total magnetic field, were taken to calculate the static pressures (thermal and magnetic) both in the upstream and downstream sides of the shocks. The variations of the solar wind parameters and pressures were then correlated with SI amplitudes. The solar wind speed variations presented good correlations with sudden impulses, with correlation coefficients larger than 0.70 both in solar maximum and solar minimum, whereas the solar wind density presented very low correlation. The parameter better correlated with SI was the square root dynamic pressure variation, showing a larger correlation during solar maximum (r =0.82) than during solar minimum (r =0.77). The correlations of SI with square root thermal and magnetic pressure were smaller than with the dynamic pressure, but they also present a good correlation, with r >0.70 during both solar maximum and minimum. Multiple linear correlation analysis of SI in terms of the three pressure terms have shown that 78% and 85% of the variance in SI during solar maximum and minimum, respectively, are explained by the three pressure variations. Average sudden impulse amplitude was 25 nT during solar maximum and 21 nT during solar minimum, while average square root dynamic pressure variation is 1.20 and 0.86 nPa1/2 during solar maximum and minimum, respectively. Thus on average, fast forward interplanetary shocks are 33% stronger during solar maximum than during solar minimum, and the magnetospheric SI response has amplitude 20% higher during solar maximum than during solar minimum. A comparison with theoretical predictions (Tsyganenko’s model corrected by Earth’s induced currents) of the coefficient of sudden impulse change with solar wind dynamic pressure variation showed excellent agreement, with values around 17 nT/nPa1/2. [Copyright &y& Elsevier]

Abstract: A statistical study of magnetic cloud parameters and geoeffectiveness is presented in this work, based on the analysis of 149 magnetic clouds during the period 1966–2001. The distributions of maximum magnetic field strength, solar wind speed and southward magnetic field inside the clouds were determined for the whole data set and for subsets classified according to the magnetic cloud polarity (rotation in Z or Y directions). The geoeffectiveness was determined by classifying the number of magnetic clouds followed by intense, moderate and weak magnetic storms, and by calm periods. It was found that around 77% of the magnetic clouds are geoeffective, i.e., they were followed by intense or moderate geomagnetic storms . Considering also weak storms , 97% of MCs were followed by geomagnetic activity. When considering polarity, each magnetic cloud subset has a slightly different geoeffectiveness, which is in agreement with the differences observed in their parameter distributions. The was observed to be the less geoeffective of the MC subsets, with 66.6% of this class events being followed by intense or moderate storms, against 73.0% of , 80.0% of the Y, 83.3% of the and 85.7% of the . The – relation was confirmed for the magnetic clouds with rotation in Z direction. [Copyright &y& Elsevier]

Abstract: The solar and interplanetary origin of space weather disturbances, as well as the related magnetospheric dynamics, will be presented. Besides the involved phenomenology in solar–terrestrial physics, some of the main effects of space weather variability concerning mankind in space and at the earth’s surface will also be discussed. The November 2003 event is shown as an example of the solar, interplanetary and magnetospheric aspects of a space weather storm. [Copyright &y& Elsevier]