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.

The results of the first 18 months of the PLASMON project are presented. We have extended our three, existing ground-based measuring networks, AWDANet (VLF/whistlers), EMMA/SANSA (ULF/FLRs), and AARDDVARK (VLF/perturbations on transmitters' signal), by three, eight, and four new stations, respectively. The extended networks will allow us to achieve the four major scientific goals, the automatic retrieval of equatorial electron densities and density profiles of the plasmasphere by whistler inversion, the retrieval of equatorial plasma mass densities by EMMA and SANSA from FLRs, developing a new, data assimilative model of plasmasphere and validating the model predictions through comparison of modeled REP losses with measured data by AARDDVARK network. The first results on each of the four objectives are presented through a case study on a space weather event, a dual storm sudden commencement which occurred on August 3 and 4, 2010.

We illustrate a semi−automated procedure to detect the field line resonance (FLR) frequencies and the derived equatorial plasma mass den− sities in the inner magnetosphere from ULF measurements recorded at the European quasi−Meridional Magnetometer Array (EMMA). FLR frequencies are detected using the standard technique based on cross−phase and amplitude ratio spectra from pairs of stations latitudi− nally separated. Equatorial plasma mass densities are then inferred by solving the toroidal MHD wave equation using the TS05 Tsyga− nenko magnetic field model and assuming a 1/r dependence of the mass density along the field line. We also present a statistical analysis of the results obtained from 165 non−consecutive days of observations at 8 station pairs covering the range of magnetic L−shells 2.4−5.5 and encompassing a wide range of geomagnetic conditions. The rate of FLR detection maximizes around local noon at each pair of sta− tions, reaching the highest values (~95%) around L = 3. A clear diurnal modulation of the FLR frequency is observed at all L values. At the lowest latitudes, the variation is characterized by a rapid decrease in the early morning hours, a stagnation in the middle of the day, and an increase in the evening hours. At higher latitudes, a continuous and more pronounced decrease of the FLR frequency is observed during all daytime hours reflecting a permanent state of recovery of flux tubes depleted by events of enhanced magnetospheric convec− tion. Consistently, the radial profiles of the inferred equatorial mass density show a density increase from morning to afternoon which gets more pronounced with increasing distance and with the level of the preceding geomagnetic activity. The results also confirm the forma− tion of the plasmapause at geocentric distances that decrease as the disturbance level increases. Mean mass density distributions in the equatorial plane are also shown in 2−D maps for different geomagnetic conditions, as well as for a representative stormy day.

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.

[1] This paper, by using the data of Cluster, TC-1, GOES, and eight ground stations on 22 October 2004, studied the characteristics of low-latitude Pi2s generated by an earthward bursty bulk flow (BBF) in the near-Earth tail plasma sheet. The BBF excited simultaneously two distinct classes of Pi2s: one is long-period Pi2 (90-130 s) and the other is short-period Pi2 ($50 s). The long-period Pi2 is transient response type Pi2 associated with field-aligned current produced by the braking of BBFs. The spectrum analysis show that the amplitude spectrum peak of long-period Pi2 increases with increasing latitude, indicating that the source is at higher latitudes. The time delay for the propagation of Alfven waves from Cluster to the Earth is very close to the time difference between the onset time of the BBFs at Cluster and the starting time of the long-period Pi2 on the ground. The short-period Pi2 is a global cavity mode since the Pi2s in H components at eight stations have almost the same starting time, same oscillation period, and same waveform, which are all typical characteristics of cavity mode. The amplitude spectrum peak of short-period Pi2 at NCK (N42.7) is larger than those at higher-station UPS (N56.5) and lower-station CST (N40.8). The polarization analysis at three lower-latitude stations shows that the polarization underwent two reversals. The major axis of the polarization ellipse points to approximately the north, indicating that the short-period Pi2s are not excited by nightside current system. TC-1 observed transverse mode Pi2s. Its period is almost identical with the periods of Pi2 on the ground, indicating they belong to the same wave.