[1] The interplanetary causes of intense geomagnetic storms and their solar dependence occurring during solar cycle 23 (1996-2006) are identified. During this solar cycle, all intense (Dst À100 nT) geomagnetic storms are found to occur when the interplanetary magnetic field was southwardly directed (in GSM coordinates) for long durations of time. This implies that the most likely cause of the geomagnetic storms was magnetic reconnection between the southward IMF and magnetopause fields. Out of 90 storm events, none of them occurred during purely northward IMF, purely intense IMF By fields or during purely high speed streams. We have found that the most important interplanetary structures leading to intense southward Bz (and intense magnetic storms) are magnetic clouds which drove fast shocks (sMC) causing 24% of the storms, sheath fields (Sh) also causing 24% of the storms, combined sheath and MC fields (Sh+MC) causing 16% of the storms, and corotating interaction regions (CIRs), causing 13% of the storms. These four interplanetary structures are responsible for three quarters of the intense magnetic storms studied. The other interplanetary structures causing geomagnetic storms were: magnetic clouds that did not drive a shock (nsMC), non magnetic clouds ICMEs, complex structures resulting from the interaction of ICMEs, and structures resulting from the interaction of shocks, heliospheric current sheets and high speed stream Alfvén waves. During the rising phase of the solar cycle, sMC and sheaths are the dominant structure driving intense storms. At solar maximum, sheath fields, followed by Sh+MCs and then by sMC were responsible for most of the storms. During the declining phase, sMC, Sh and CIR fields are the main interplanetary structures leading to intense storms. We have also observed that around 70% of the storms follow the interplanetary criteria of Ey ! 5 mV/m for at least 3 h. Around 90% of the storms used in the study followed a less stringent set of criteria: Ey ! 3 mV/m for at least 3 h. Finally, we obtain the approximate rate of intense magnetic storms per solar cycle phases: minimum/rising phase 3 storms.year À1 , maximum phase 8.5 storms.year À1 , and declining/minimum phases 6.5 storms.year À1 .

We present a review on the interplanetary causes of intense geomagnetic storms (Dst ≤ −100 nT), that occurred during solar cycle 23 (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005). It was reported that the most common interplanetary structures leading to the development of intense storms were: magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud and corotating interaction regions at the leading fronts of high speed streams. However, the relative importance of each of those driving structures has been shown to vary with the solar cycle phase. Superintense storms (Dst ≤ −250 nT) have been also studied in more detail for solar cycle 23, confirming initial studies done about their main interplanetary causes. The storms are associated with magnetic clouds and sheath fields following interplanetary shocks, although they frequently involve consecutive and complex ICME structures. Concerning extreme storms (Dst ≤ −400 nT), due to the poor statistics of their occurrence during the space era, only some indications about their main interplanetary causes are known. For the most extreme events, we review the Carrington event and also discuss the distribution of historical and space era extreme events in the context of the sunspot and Gleissberg solar activity cycles, highlighting a discussion about the eventual occurrence of more Carringtontype storms.

[1] There has been considerable confusion in the literature about what mirror mode (MM), magnetic decrease (MD), and linear magnetic decrease (LMD) structures are and are not. We will reexamine past spacecraft observations to demonstrate the observational similarities and differences between these magnetic and plasma structures. MM structures in planetary magnetosheaths, cometary sheaths, and the heliosheath have the following characteristics: (1) the structures have little or no changes in the magnetic field direction across the magnetic dips; (2) the structures have quasiperiodic spacings, varying from ∼20 proton gyroradii (r p ) in the Earth's magnetosheath to ∼57 r p in the heliosheath; and (3) the magnetic dips have smooth edges. Magnetosheath MM structures are generated by the mirror instability where b ? /b k > 1 + 1/b ? (b is the plasma thermal pressure divided by the magnetic pressure). In general, the sources of free energy for the mirror instability are reasonably well understood: shock compression, field line draping, and, in the cases of comets and the heliosheath, also ion pickup. The observational properties of interplanetary MDs are as follows: (1) there is a broad range of magnetic field angular changes across them; (2) their thicknesses can range from as little as 2-3 r p to thousands of r p , with no "characteristic" size; and (3) they typically are bounded by discontinuities. The mechanism(s) for interplanetary MD generation is (are) currently unresolved, although at least five different mechanisms have been proposed in the literature.

The interplanetary causes of superintense geomagnetic storms (superstorms, Dst ≤ −250 nT) that occurred during solar cycle 23 are studied. Eleven superstorms occurred during the cycle, five close to solar maximum (2000–2001) and six in the post‐maximum/declining phase (2003–2004). About 1/3 of the superstorms were caused by magnetic clouds (MCs), 1/3 by a combination of sheath and MC fields, and 1/3 by sheath fields alone. The interplanetary parameter best correlated with peak Dst was the time‐ integrated Ey during the storm main phase (in contrast with peak Bs and/or peak Ey for less intense geomagnetic storms). The range of peak Dst for these storms was −263 to −422 nT. The storm main phase durations had a range of 3–33 h. We conclude from this study that: (1) only MCs and/or interplanetary sheaths had fields intense enough and with long enough durations to cause superstorms; (2) superstorms occurred only in the maximum and declining phases; (3) the total energy transferred from the solar wind to the magnetosphere is best correlated with the time‐integrated solar wind Ey parameter.

Jupiter is a complex and at the same time very powerful radio source in the decameter wavelength range. The emission is anisotropic, intrinsically variable at millisecond to hour timescales, and also modulated by various external processes at much longer periods, ranging from ∼10 h to months or years (including Jovian day and year, solar activity and solar wind variations, and for groundbased observations, terrestrial day and year). As a consequence, long-term observations and their statistical study have proved to be necessary for disentangling and understanding the observed phenomena. We have built a database from the available 26 yr of systematic, daily observations conducted at the Nançay Decameter Array and recorded in digital format. This database contains all observed Jovian decametric emissions, classified with respect to the time-frequency morphology, their dominant circular polarization, and maximum frequency. We present the results of the first statistical analysis of this database. We confirm the earlier classification of Jovian decameter emissions in Io-A, -A , -B, -C, -D and non-Io-A, -B, -C types, but we also introduce new emission types (Io-A and Io-B ) and precise and characterize the non-Io-D type. We determine the contours of all emission types in the CML−Φ Io plane (Central Meridian Longitude in Jupiter's System III coordinates versus Io Phase), provide representative examples of their typical time-frequency patterns, and the distribution of emission's maximum frequency as a function of Λ Io (Io's Longitude). Finally, we present a statistical analysis of the distributions of the occurrence rate, duration, intensity and polarization for each emission type. non-Io-DAM appears to be related to small-scale, possibly bursty auroral structures.