Multi-instrument analysis of the ionospheric signatures of a hot flow anomaly occurring on July 24, 1996

• We present the analysis of a coordinated set of observations from the POLAR ultraviolet imager (UVI), ground magnetometers, incoherent scatter radar, solar wind monitors, and the DMSP satellite, focused on a traveling convection vortex (TCV) event on July 24, 1996. Starting at approximately 1036 UT, ground magnetometers in Greenland and eastern Canada observe pulsations consistent with the passing overhead of a series of TCV field-aligned current pairs. Azimuthal scans by the Sondrestrom incoherent scatter radar located near Kangerlussuaq (formerly Sondrestrom), Greenland, at this time show strong modulation in the strength and direction of ionospheric plasma flow. The magnetometer pulsations grow in magnitude over the next hour, peaking in intensity at 1137 UT. Images from the UVI instrument show a localized intensification of auroral emissions over central and western Greenland at 1139 UT. Subsequent images show the intensification grow in strength and propagate westward (tailward) until approximately 1158 UT, at which time the intensification fades, These observations are consistent with the westward passage of four pairs of TCVs over central Greenland. The intensification of auroral emissions at 1139 UT is associated with the leading vortex of the fourth TCV pair, thought to be the result of an upward field-aligned current. The modulated flow observed by the radar is the result of the strong electric fields associated with the field-aligned current systems responsible for the impulsive TCV as they pass through the field of view of the radar. Measurements taken in the solar wind by the Wind spacecraft suggest that a pressure change triggers the onset of TCV activity. A subsequent sudden change in the orientation of the interplanetary magnetic field produces a hot flow anomaly which forms at the bow shock. We believe that the interaction of the hot flow anomaly with the magnetopause intensified the fourth TCV pair and. produced the associated auroral brightening. DMSP particle data indicate that the TCVs occur on field lines which map to the boundary plasma sheet-low latitude boundary layer interface. The ground observations associated with the hot flow anomaly are the first of their kind and provide a mechanism to tie an interplanetary magnetic field orientation change into the existing theory that TCVs result from a deformation of the magnetopause.

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NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

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