Thermospheric Winds in an Intense Auroral Substorm: The HEX-2 Sounding Rocket Missions
Abstract
Thermospheric composition at high latitudes is altered through heating in auroral substorms and geomagnetic storms. The HEX-1 investigation in March 2003 targeted a stable, quiet arc to directly observe the upward, vertical winds believed to be driven by this heating. However, no upward winds were observed. A logical conclusion at the time was that too little energy was delivered to drive the anticipated vertical motions in the thermosphere. To test this, a more complex HEX-2 investigation was executed with rocket flights into the lower thermosphere under conditions of intensely active auroral. Specifically, four sounding rockets were launched within 16 minutes into intense aurora on February 14, 2007, some 42 minutes after substorm onset. The flights were designed to release six nearly vertical TMA puffed trails over a range of altitudes, as well as a single nearly horizontal trajectory created, as in HEX-1, by an in-flight reorientation of the third stage before ignition and subsequent dispersal of TMA at nearly constant altitude over a wide range of latitudes. Neutral wind vectors were obtained by ground-based triangulation of individual TMA puffs. Densities and temperatures were obtained on all up and down legs of the vertical trajectories with cold cathode ionization gauges. The SuperDARN and AMISR radars provided concurrent observations of the ionosphere. As expected, the two missions observed quite dissimilar wind fields. But unexpectedly, HEX-2 encountered a weaker and more spatially uniform wind field than HEX-1, despite HEX-2 having flown during much more disturbed geomagnetic conditions. Equally unexpectedly, HEX-2 also failed to observe any significant upward wind. These and other observations will be presented and discussed, along with some developing interpretations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFMSA33A1061W
- Keywords:
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- 0310 Airglow and aurora;
- 0355 Thermosphere: composition and chemistry;
- 3369 Thermospheric dynamics (0358);
- 7954 Magnetic storms (2788)