First Results From OI (6300A) Fringe Measurements Using the TIMED Doppler Interferometer (TIDI)

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0310 Airglow And Aurora, 0355 Thermosphere: Composition And Chemistry, 3369 Thermospheric Dynamics (0358)

Scientific paper

The TIMED Doppler Interferometer, TIDI, began synoptic observations of the upper thermosphere on 25 September 2008. The routine science mode was adjusted to view the Earth's limb at tangent heights from 160 to 300 km at 20 km increments at 4 seconds per altitude sample. The full mesosphere/thermosphere scan sequence is repeated every 100 seconds. This sequence provides approximately 60 altitude scans per orbit, and there are nearly 15 orbits per day. The precession rate of the TIMED satellite is slow (12 minutes per day) implying that TIDI samples any latitude circle every 24 degrees of longitude at approximately the same dayside Local Solar Time (LST) and the same nightside LST. Finally, TIDI is a multiplex instrument monitoring four tangent points during every integration which allows the measurement of the horizontal neutral wind via Doppler shifted OI (6300A) airglow emission. First look altitude brightness profiles indicate feeble OI (6300A) emission during the current minimum phase of the solar cycle. Brightness profiles peak in the neighbourhood of 220 to 240 km altitude at low latitudes on both the dayside and on the nightside. Brightness registration on global latitude/longitude charts show auroral oval brightening for winter nightside measurements. At the time of this writing, the highest Ap and Kp levels recorded since the initiation of the new TIDI mode occurred on 11 October 2008 (37 and 7 respectively). TIMED beta angle was -71.98 degrees on this date suggesting flight, as well as TIDI sampling, near the dawn/dusk terminator. TIDI cold side telescopes were able to observe nightside OI (6300A) airglow at southern latitudes and did record significant (2 orders of magnitude) enhancement in brightness in the upper thermosphere. There is no question that TIDI samples OI (6300A) thermospheric airglow. The volume emission rate is at extremely low levels during the present solar minimum period. It is anticipated that brightness levels will increase at least four-fold as the solar cycle progresses to maximum in the next few years. Neutral wind results from TIDI will improve as the instruments 'zero-wind' position is determined and constrained. This paper will also describe current 'best-effort' wind results determined from preliminary 'zero-wind' estimates.

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