Coordinated ISTP satellite and ground observations of morningside Pc5 waves

Abstract

Abstract. This paper reports the result of a coordinated data analysis of a morningside Pc5 event observed at different altitudes in the magnetosphere and also on the ground. The event took place during 1400-1500 UT of April 29, 1993. The Geotail satellite was located in the boundary region and observed a 5-min quasi-periodic magnetic oscillation. The oscillation was mostly transverse to the background magnetic field. A 90 ø phase lag between the magnetic field and electric field variations was not clear, suggesting that the oscillation was not a standing wave and that Geotail was located in or close to the excitation region. The plasma flow vector rotated clockwise on the equatorial plane viewed from the north as expected for a magnetospheric surface wave on the morningside. At geosynchronous altitude, the GOES satellites also observed a 5-min magnetic oscillation but with a significantly smaller amplitude than at the Geotail position. Five-minute magnetic oscillations were also detected at Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) and Magnetometer Array for Cusp and Cleft Studies (MACCS) ground stations in the same local time sector as the satellites, even equatorward of a region 2 field-aligned current observed by the Freja magnetometer data. From the phase analysis of ground signatures, the wave is inferred to propagate westward (antisunward) at a velocity of 18 ø in longitude per minute. The propagation speed mapped to the equator, 400 km/s, is in the range of the expected flow speed of the magnetosheath. It is inferred that in the present event, the Kelvin-Helmholtz instability at the magnetopause, rather than at the inner edge of the boundary layer, excited an oscillation at the single frequency in a large area from the boundary region to deep inside the magnetosphere.

Mapping of the quasi-periodic oscillations at the flank magnetopause into the ionosphere

“…Station B15 recorded two different frequencies during Event 6, one of which was within 0.1 mHz of the two Cluster dominating frequencies. Events 1, 5, and 6 were similar to the previously published results obtained by Ohtani et al (1999) whom discovered dominating frequencies within 0.2 mHz of the spacecraft frequency. All oscillation frequencies were higher in the ground magnetometer data than the Cluster data.…”

“…These magnetic latitudes were less than the latitudes at which Lui (1989) and Farrugia et al (1994) observed their auroral bright spots and where McHenry et al (1990) observed traveling convection vortices. The mapped magnetic latitude range was similar to where Ohtani et al (1999) observed the Pc5 magnetometer pulsations.…”

“…The ionospheric magnetic local time ranged between 5.0 to 13.8 h in the Northern Hemisphere and 4.9 to 11.9 h in the Southern Hemisphere. These magnetic latitudes were similar to the latitudes at which Lui (1989) and Farrugia et al (1994) observed their auroral bright spots, where Ohtani et al (1999) observed the Pc5 magnetometer pulsations, and where McHenry et al (1990) observed traveling convection vortices. They were also mapped to significantly higher magnetic latitudes than the global MHD models.…”

“…Magnetic oscillations varied up to [35,25,20] nT in the X, Y , and Z directions, respectively. The oscillation periods varied from 1 to 7 min, generally falling within the Pc5 range as suspected by Ohtani et al (1999). Table 10 documents the signature results from SuperMAG.…”

“…Low-frequency magnetic pulsations in the Pc5 range have been suggested as the effect of KHI when observed in the dawn region as studied by Ohtani et al (1999). The Pc5 range lies between 1 and 10 mHz, having a period of 1.6 to 16 min.…”