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.

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 variation of the spectral characteristics of daytime Pc3 geomagnetic pulsations recorded at L'Aquila (Italy, L ∼ 1.6) during one solar cycle (1985–1994) is investigated on a yearly time scale. We find in the frequency domain two peaks in the event distribution for the H component during years of minimum solar activity and a single peak during years of maximum solar activity. These features can be interpreted in terms of the solar cycle variation of the predicted dominant frequency of the main driving source (upstream waves) as well as of the local fundamental field line eigenfrequency. The dominant frequency for the D component also changes according to the expected solar cycle variation of the dominant source frequency. The solar cycle variation of the estimated fundamental field line eigenfrequency is consistent with a general increase of the plasmasphere density along the local field line by a factor of ∼2 from minimum to maximum solar activity which is in agreement with theoretical models.

We present a statistical analysis of Pc3–4 pulsations during 2005 at two polar cap stations (Terra Nova Bay and Dome C, Antarctica) and, for comparison, at a low‐latitude station (L'Aquila). The analysis technique allows to discriminate the signal component from the background noise in the power spectrum and to determine the frequency of such ULF signal, commonly associated to the upstream wave source. The comparison of data makes evident that the characteristics of the ULF pulsations are different at low and high latitudes, and significant differences emerge also between the two polar cap stations. At Dome C the ULF signals are observed during the whole day, while at Terra Nova Bay and at L'Aquila the signals are mainly observed in the dayside sector. The different cone angle dependence at L'Aquila and Dome C, the steeper slope in the frequency dependence on the interplanetary magnetic field strength at Dome C with respect to L'Aquila and Terra Nova Bay and the time dependence of the coherence between pulsations at the Antarctic stations suggest that at low‐latitude waves are transmitted to the ground from a region close to the subsolar bow shock, while near the geomagnetic pole waves are mainly transmitted through the magnetotail lobes. At Terra Nova Bay, where the local field lines approach the cusp around noon and are stretched into the magnetotail around midnight, the transmission path seems to be time dependent, with daytime and nighttime pulsations penetrating through the subsolar point and via the magnetotail lobes, respectively.

[1] In this study we analyzed a long-duration ULF wave event detected on 18-19 February 2005 by Cluster satellites, upstream of the nose of the bow shock. The availability of simultaneous data from Geotail satellite, located in the foreshock region close to the dawn flank of the bow shock, allowed us to make a comparison between the observations at the two different sites. The results can be explained in terms of local wave generation, depending on the orientation of the interplanetary magnetic field with respect to the local bow shock normal. In addition, simultaneous data from Polar satellite in the inner magnetosphere and from ground stations in the southern polar cap and at low latitude allowed us to investigate the transmission of the external waves through the magnetosphere up to the ground. The observations suggest different paths of transmission. Waves generated upstream of the bow shock nose directly transmit near the subsolar point, progressively propagate into the magnetosphere and, after conversion into field-guided Alfven modes, reach the ground at high and low latitudes; waves generated on the flanks of the bow shock do not affect the subsolar magnetosphere, and consequently, there is no propagation along the closed field lines at both high and low latitudes. On the other hand, near the geomagnetic pole, the occurrence of pulsations can be related to the transmission across the magnetopause flanks of upstream waves, anywhere generated, as they are convected downstream by the solar wind; the compressional waves do not propagate deeply into the tail lobes but can couple to Alfven-guided waves along the outermost field lines.Citation: Francia, P., M. Regi, M. De Lauretis, U. Villante, and V. A. Pilipenko (2012), A case study of upstream wave transmission to the ground at polar and low latitudes,