Magnetic field and plasma data of Helios 1 and 2 between 0.3 and 1 AU have been used to investigate the Alfvénic character of the solar wind fluctuations with periods above 1 hour. Clear evidence for the existence of very long period Alfvén waves, up to ∼15 hours (in the spacecraft frame) close to the sun, has been obtained. The observations at different heliocentric distances suggest that the longest wavelengths are removed from the Alfvénic regime leaving the sun.

During June–July 2002 the low‐altitude (h ∼ 400 km) Challenging Minisatellite Payload (CHAMP) satellite passed approximately every 2nd day close to the South European Geomagnetic Array (SEGMA, 1.56 < L < 1.88) during daytime hours. We present here the analysis of a Pc3 geomagnetic pulsation event observed simultaneously in space and at the ground array during the conjunction of 6 July 2002. Both compressional and transverse oscillations were identified in CHAMP magnetic measurements. A close correspondence between the compressional component and the ground signals is observed. The behavior of the CHAMP azimuthal component shows evidence for the occurrence of a field line resonance at L ≅ 1.6. The frequency of these azimuthal oscillations is ∼20% higher than the frequency of both the compressional oscillation and the ground pulsations. Such a difference is explained in terms of a sort of Doppler shift caused by the fast movement of the satellite across the resonance region where the phase signal changes rapidly. A further analysis verifies for the first time by space measurements the theoretical pattern of the wave polarization sense in the resonance region. The comparison with corresponding SEGMA measurements also provides an unprecedented direct confirmation of the well‐known 90° rotation of the ULF wave polarization ellipse through the ionosphere.

A statistical study of magnetic field discontinuities for the interval February to October 1968 using data from the NASA Goddard Space Flight Center/University of Rome experiment on Pioneer 8 has been conducted. High-resolution data (10-sec averages) have been employed, stringent criteria bei, ng utilized to select more than 16,000 events, about 50% being identified as disturbances that are probably tangential discontinuities (TD). Near 1 AU the average occurrence rate of discontinuities is about 3.6/hr, whereas that of tangentiallike discontinuities is about 1.6/hr. The rate of occurrence of discontinuities is found to be correlated with the directional change of the field across the discontinuity surface. The normal to the TD discontinuity plane is most often perpendicular to the Archimedean spiral field configuration. A decrease of the rate of occurrence of TD is found with increasing heliocentric distance and/or with decreasing heliographic latitude. Possible interpretations of the effect are discussed.

Abstract. Ionospheric TEC (Total ElectronContentThis local TEC disturbance arises preparatory to the EQ main shock occurred at 01:32 UT on 06 April 2009, maximizes its amplitude of ~ 0.8 TECu after the shock moment and disappears after it. The TEC disturbance was localized at heights below 160 km, i.e. in the lower ionosphere.

The definite identification of the characteristics of the geomagnetic response to solar wind pressure changes represents an interesting element of magnetospheric dynamics that is also important in the Space Weather context. In the present analysis the aspects of the global response in ground‐based observations have been examined for three case events, discriminating between magnetospheric and ionospheric contributions in ground manifestations of sudden impulses (SI). The separation between the magnetospheric and ionospheric contributions is obtained by a comparison between the observations at geostationary orbit and the predictions of the Tsyganenko and Sitnov (2005) model for the different magnetospheric current systems (from the magnetopause, ring current, tail current, etc.). The magnetopause current is the key element for the SI variation observed at geosynchronous orbit in a wide local time sector and practically represents the DL field of magnetospheric origin. The expected DL field is then subtracted, at each ground station, from the experimental measurements, in order to obtain a confident estimate of the residual DP field at different latitudes and local times. After evaluating the contribution of the field‐aligned currents, we estimate the ionospheric current flow pattern of the preliminary and main impulses (PIIC and MIIC). The patterns of PIIC and MIIC fields are consistent with those proposed by Araki (1994). Some “anomalous” ground manifestations can be interpreted in terms of the combined effect of the irregular configuration of the boundary of the vortices of the ionospheric currents, of the rapid temporal evolution of the entire pattern, and of the station rotation beneath the pattern.

Interplanetary observations from Helios 1, Helios 2, and IMP-8 spacecraft during 1976 and 1977, namely the early portion of solar cycle 21, have been used to investigate the latitudinal gradients of the solar wind parameters with respect to the angular displacement from the current sheet inferred from synoptic HAt white-light maps of the solar corona at 1.75 solar radii. A latitudinal belt of + 25 deg around the current sheet has been investigated. Large gradients for solar wind flow speed, proton density and temperature have been found, Smoother gradients were also found for particle flux, kinetic, gravitational and thermal energy density flux. All these gradients revealed to become smoother going towards the solar cycle's maximum. Neither latitudinal nor temporal variations were identified for magnetic and thermal energy density. A remarkable result of this study is that the momentum flux density and the total energy flux density which other authors found to be independent of any longitudinal stream structure were also found to be independent of any latitudinal structure. Moreover, these two parameters did not show any temporal variation during the period of interest.

An analysis of sudden impulses (SI) at geosynchronous orbit (2000–2004) confirms a general dependence of the SI amplitude on the variation of the square root of the solar wind pressure, together with an explicit LT dependence, with greater responses at satellites located closer to noon meridian. In the dayside hemisphere the magnetospheric response, which mostly influences the Bz component, is well consistent with the magnetic field jump expected for changes of the magnetopause current alone, driven by changes of the solar wind pressure. In the dark hemisphere, where the changes of the Bx component are often relevant, the competing contributions of several current systems (from the magnetopause, cross‐tail current, ring current, Birkeland current) determine a large variety of responses that cannot be interpreted in a statistical sense. Depending on the solar wind conditions, different situations emerge for nightside events. We present a case in which a remarkable magnetospheric compression determined field variations which can be interpreted in terms of a strongly dominant contribution of the magnetopause current even in the midnight sector, while in other cases the observed features are consistent with the predictions of the global current system. We also speculated that additional elements (such as the geocentric distance of the hinging point, the separation point between closed and open field lines in the geomagnetic tail) might play a crucial role in determining the aspects of the magnetospheric response. The correspondence between model predictions and observations persists even in cases of moderate Southward orientations of the IMF.

A full-halo coronal mass ejection left the sun on June 21, 2015 from the active region NOAA 12371 encountering Earth on June 22, 2015, generating a G3 strong geomagnetic storm. The CME was associated with an M2 class flare observed at 01:42 UT, located near the center disk (N12E16). Using satellite data from solar, heliospheric, magnetospheric missions and ground-based instruments, we performed a comprehensive Sun-to-Earth analysis. In particular, we analyzed the active region evolution using ground-based and satellite instruments (BBSO, IRIS, HINODE, SDO/AIA, RHESSI --Halpha, EUV, UV, X), the AR magnetograms, using data from SDO HMI, the relative particle data, using PAMELA instruments and the effects of interplanetary perturbation on cosmic ray intensity. We also evaluated the