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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]

The interaction and response of the magnetic cloud-type structure with Earth's magnetosphere were modeled by the SWMF/BATS-R-US code. The conversion of magnetic (Em), kinetic (Ek), and internal (Ei ) energies was analyzed as well as the wave power integrated in the ultra-low frequency (ULF) range of the poloidal (Eϕ) and toroidal (Er ) electric field components in the equatorial region of the magnetosphere, in seven 2-hr long intervals, namely, I1 through I7. The intensity of energy conversion and wave activity for I1 and I7 intervals was negligible. The energy conversion started in the I2 interval and extended to the I3, I4, and I5 intervals. The power of the Eϕ and Er components in the dayside and nightside regions is clearly observed. The I4 corresponds to interplanetary magnetic field (IMF) Bz mostly southward and the I5 has similar amplitudes of the Bz and By components, corresponding to the period of the high geomagnetic activity. The conversion rate for the I4 and I5 was similar, however, the integrated power spectral density (IPSD) of the Eϕ and Er components is more intense in I5. During the I6 interval, with predominant IMF By, the energy conversion rate is intensified mostly for inner radial distances R < 6 RE, and the Ek component becomes close to zero for outer regions. The energy conversion regions are located spatially close to or overlapping with regions where the IPSD in the ULF range is intensified. The energy conversion in the inner magnetosphere occurred preferentially between Em and Ei, with the Ek energy component always present but with lower intensities. [ABSTRACT FROM AUTHOR]

Using global magnetohydrodynamic (MHD) simulations, we investigate the role played by a complex solar structure composed of a corotating interaction region (CIR) followed by solar wind Alfvénic fluctuations on the magnetosphere's nightside, equatorial electric field oscillations in the ultra-low-frequency range. A series of numerical experiments are performed employing synthetic solar wind inputs resembling those of a real CIR+Alfvénic fluctuation event that reached Earth's magnetosphere on 2003 April 20. The following is found: (i) Radial electric field component fluctuations are excited via magnetopause boundary motions driven either by solar wind density variations characteristic of CIRs or by solar wind Alfvénic fluctuations with a given oscillation period. (ii) Azimuthal electric field component fluctuations nearer to Earth, that is, at radial distances R less than about 5RE (Earth radius), are apparently not related to either of the two types of sinusoidal solar wind Alfvénic fluctuations used in this study featuring monochromatic frequencies of 0.833 mHz (20-minute period) and 1.666 mHz (10-minute period). Instead, these innermost azimuthal component fluctuations show enhanced activity when inner magnetosphere convection increases as a result of a southward turning of the interplanetary magnetic field component Bz. (iii) Lastly, outermost (R ≳ 7 RE) azimuthal electric field oscillations weakly respond to monochromatic solar wind Alfvénic fluctuations by showing power spectral density peaks at both driving frequencies, but only near the flanks of the magnetopause, thus suggesting that such oscillations are being excited also owing to magnetopause boundary motions driven by solar wind Alfvénic fluctuations. [ABSTRACT FROM AUTHOR]

Fast interplanetary shocks occurrence, their parameters, and drivers near Jupiter's orbit are determined in this paper. It was found that 70% of the fast shocks are forward (FS) and 30% are reverse (RS). Interplanetary coronal mass ejection‐driven FS occur more frequently in all solar cycle phases except in the declining phase, when corotating interaction region‐driven shocks predominate. Most of the shocks were quasi‐perpendicularly (65° to 70°) propagating relative to the ambient interplanetary magnetic field. The average shock magnetosonic Mach number is slightly higher for FS (2.6) than for RS (2.4), which in turn are stronger than shocks near 1 and 10 AU reported in previous works. This occurs because of the full development of corotating interaction region shocks and higher occurrence of strong interplanetary coronal mass ejections near 5 AU and that the magnetosonic speed at 5 AU has only 60% of its value at 1 AU. Plan Language Summary: Interplanetary shock waves are sudden variations in solar wind plasma and magnetic field parameters. They propagate in the interplanetary space and have important effects on planetary magnetospheres. For instance, shocks cause expansions and compressions of Jupiter's magnetosphere and trigger its auroral emissions. In this work plasma and magnetic field data from several spacecraft that crossed interplanetary space near Jupiter's orbit space are analyzed. A list of interplanetary shocks is compiled, and their parameters and drivers are determined. It was found that shocks at 5 AU have preferentially a quasi‐perpendicular propagation to the magnetic field direction and are on average stronger than shocks observed near Earth's orbit. Key Points: Interplanetary shock occurrence, parameters, and drivers near Jupiter's orbit are determinedThere are about 70% fast forward and 30% reverse shocks; about 90% of RS are CIR driven, while 45% of FS are CIR driven and 55% are ICME drivenShocks at 5 AU are mostly quasi‐perpendicularly propagating and stronger on average than shocks at 1 AU [ABSTRACT FROM AUTHOR]

The interplanetary and geomagnetic characteristics of High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events are studied using wavelet analysis technique. The Morlet wavelet transform was applied to the 1 min interplanetary magnetic field (IMF) Bz component and the geomagnetic AE index during HILDCAA events. We have analyzed the AE data for the events occurring between 1975 and 2011, and the IMF Bz data (both in GSE and GSM) for the events between 1995 and 2011. We analyzed the scalograms and the global wavelet spectrum of the parameters. For 50% of all HILDCAA events, the main periodicities of the AE index are generally between 4 and 12 h. For the Bz component, the main periodicities were found to be less than 8 h for ~56% of times in GSM system and for ~54% of times in GSE system. It is conjectured that the periodicities might be associated with the Alfvén waves which have typical periods between 1 and 10 h. The results are discussed in the light of self organized criticality theory where the physical events have the capacity of releasing a considerable amount of energy in a short interval of time. [ABSTRACT FROM AUTHOR]

We examine particularly intense substorms (SML ⩽ -2500 nT), hereafter called "supersubstorms" or SSS events, to identify their nature and their magnetic storm dependences. It is found that these intense substorms are typically isolated events and are only loosely related to magnetic storms. SSS events can occur during super (Dst ⩽ -250 nT) and intense (-100 nT⩾Dst> -250) magnetic storms. SSS events can also occur during nonstorm (Dst ⩾ -50 nT) intervals. SSSs are important because the strongest ionospheric currents will flow during these events, potentially causing power outages on Earth. Several SSS examples are shown. SSS events appear to be externally triggered by small regions of very high density (∼30 to 50 cm-3/ solar wind plasma parcels (PPs) impinging upon the magnetosphere. Precursor southward interplanetary magnetic fields are detected prior to the PPs hitting the magnetosphere. Our hypothesis is that these southward fields input energy into the magnetosphere/magnetotail and the PPs trigger the release of the stored energy. [ABSTRACT FROM AUTHOR]

The influence of solar wind conditions on the Jovian auroral radio emissions has long been debated, mostly because it has always been difficult to get accurate solar wind and radio observations at the same time. We present here a study of Jupiter's radio emissions compared to solar wind conditions using radio (RPWS) and magnetic (MAG) data from the Cassini spacecraft from October to December 2000, just before its flyby of Jupiter. The spacecraft was then in the solar wind and could record both the radio emissions coming from the Jovian magnetosphere and the solar wind magnetic field (IMF). With these data, we found a good correspondence between the arrival of interplanetary shocks at Jupiter and the occurrence of radio storms. Our results confirm those from the previous studies showing that fast forward shocks (FFS) trigger mostly dusk emissions, whereas fast reverse shocks (FRS) trigger both dawn and dusk emissions. FFS-triggered emissions are found to occur 10-30 h after the shock arrival when the IMF is weak (below 2 nT), and quasi-immediately after shock arrival when the IMF is strong (above 2 nT). FRS-triggered emissions are found to occur quasi-immediately even when the IMF is weak. We show and discuss in depth the characteristic morphologies of the radio emissions related to each type of shock and their implications. We also used simultaneous radio observations from the ground-based Nançay decameter array and from the Galileo radio instrument (PWS). From the comparison of these measurements with Cassini's, we deduce the regions where the radio storms occur, as well as the radio source subcorotation rates. We show that FFS-triggered emissions onset happens in a sector of local time centered around 15:00 LT, and that all the shock-triggered radio sources sub-corotate with a subcorotation rate of ∼50% when the IMF is below 2 nT and of∼80% when it is above 2 nT. These rates could correspond to the extended and compressed states of the Jovian magnetosphere. [ABSTRACT FROM AUTHOR]

Abstract: Extreme historical and space era geomagnetic storms ( or ) are studied in terms of their sunspot and Gleissberg solar cycle distributions. Interplanetary and magnetospheric processes associated with the Carrington storm are summarized and the intense storm of August 4, 1972 is discussed in the context of the possibility of having occurred as an extreme storm instead, if the polarity of the related magnetic cloud would have been opposite. We also discuss about superintense geomagnetic storms () that occurred in the space era, showing their solar cycle and seasonal distributions and also providing averages for the peak values of their main associated interplanetary parameters. A discussion about the possible occurrence of more Carrington type storms is also addressed. [Copyright &y& Elsevier]

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]

Minima in geomagnetic activity (MGA) at Earth at the ends of SC23 and SC22 have been identified. The two MGAs (called MGA23 and MGA22, respectively) were present in 2009 and 1997, delayed from the sunspot number minima in 2008 and 1996 by ∼1/2-1 years. Part of the solar and interplanetary causes of the MGAs were exceptionally low solar (and thus low interplanetary) magnetic fields. Another important factor in MGA23 was the disappearance of equatorial and low latitude coronal holes and the appearance of midlatitude coronal holes. The location of the holes relative to the ecliptic plane led to low solar wind speeds and low IMF (Bz) variances (σBz2) and normalized variances (σBz2/B02 ) at Earth, with concomitant reduced solar wind-magnetospheric energy coupling. One result was the lowest ap indices in the history of ap recording. The results presented here are used to comment on the possible solar and interplanetary causes of the low geomagnetic activity that occurred during the Maunder Minimum. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the coupling between the solar wind and the magnetospheric cusp during the passage of a Corotating Interaction Region (CIR) high-speed stream. A CIR event on 11 January 2002 is selected for this study. We use ACE (Advanced Composition Explorer) and Geotail plasma and magnetic field data for interplanetary solar wind observations and Cluster plasma and magnetic field data for the cusp observations. The response of the solar wind on the polar cusp was studied and made visible with the wavelet and cross-wavelet analysis. During the CIR event we observe significantly enhanced wave power for waves with periods ranging from 15 to 25min (1.1–0.7mHz). Significant cross-correlation power of the ACE and Geotail interplanetary magnetic field (IMF) Bz- and Ey-component and the solar wind Vx-component versus the Cluster cusp H+ density, the thermal temperature and energetic electron flux (50–244keV) were found at the corresponding frequencies. We conclude that the solar wind Alfvén waves affect the magnetospheric dayside cusp density and heat the cusp. We interpret these correlation results as evidence of high-speed solar wind—magnetosphere coupling driven by waves in the solar wind. [ABSTRACT FROM AUTHOR]

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: Foreshock and magnetosheath waves in Uranus and Neptune magnetospheres are studied in this work with wavelet analysis. In order to conduct this study, Voyager-2 magnetometer 3-s averaged data are used. The Morlet wavelet transform is applied to the magnetic field vector data. Waves present in the magnetosheath and foreshock regions are highly non-stationary, showing large amplitude variations. It was found that the dominant periods of these waves are longer than the H+ cyclotron period. Overall, high frequency waves are seen near the bow shock crossing and low frequency oscillations near the magnetopause crossing. It can be concluded that non-stationary foreshock and magnetosheath planetary waves can be well characterized with wavelet analysis. [Copyright &y& Elsevier]