Latitudinal variations of neutral wind structures in the lower thermosphere for the March equinox period |
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| Institution: | 1. MIT Haystack Observatory, Westford, MA 01886, USA;2. SRI International, Menlo Park, CA 94025, USA;3. High Altitude Observatory, NCAR, Boulder, CO 80307, USA;4. CRESS, York University, 4700 Keele St. Toronto, ON, Canada M3J 1P3;5. Miami University, Oxford, OH 45056, USA;1. Institute of Ionosphere, National Center for Space Research and Technology, Almaty 050020, Kazakhstan;2. Institute for Physics, Southern Federal University, Rostov-on-Don 344090, Russia;3. Hacettepe University, Dept. of Electrical and Electronics Engineering, Ankara 06800, Turkey;1. Department of Physics, University of Lagos, Akoka, Yaba, Lagos, Nigeria;2. International Centre for Theoretical Physics, Trieste, Italy;3. Department of Physics, Lagos State University, Ojo, Lagos, Nigeria;4. Department of Applied Physics, S. V. National Institute of Technology, Surat, India;5. Centre for Atmosph. Research, National Space Research and Development Agency, Ayingba, Nigeria;6. Institute for Scientific Research, Boston College, Chestnut Hill, MA, USA;1. College of Geomatics, Xi''an University of Science and Technology, Xi''an, 710054, China;2. School of Geodesy and Geomatics, Wuhan University, Wuhan, 430079, China;3. Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan University, Wuhan, 430079, China |
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| Abstract: | Neutral winds in the lower thermosphere (95–) measured during the March equinox period (1991–1992) by ground-based incoherent scatter radars at Arecibo (18°N), Millstone Hill (42.5°N), and Sondrestrom (67°N) and by the space-based wind imaging interferometer (WINDII) are compared and show overall good agreement but some differences. At 18°N, the wind field in the altitude region of 95– displays prevailing upward propagating diurnal tides with wavelengths of about . The diurnal structure is affected by the semidiurnal tide resulting in regular minima separated by 11–. At altitudes above , the diurnal tide dominant wind structure changes to the semidiurnal tide dominant structure as illustrated clearly by WINDII data with coverage. Winds at 42.5°N and 67°N show similar structures in which winds at 105– are generally anti-sunward. Daytime ISR winds show prevailing upward propagating semidiurnal tides with wavelengths of 35–. Winds from WINDII reveal the existence of the in situ thermospheric diurnal tide with amplitudes comparable to those of the semidiurnal tide. The superimposition of the two tides result in a wind field stronger during daytime than during nighttime at mid- and high-latitudes. Geomagnetic influence on neutral winds is negligible at low- and mid-latitudes under solar quiet conditions, but is observed at high-latitudes, where wind vectors follow a clockwise one-cell pattern at altitudes above about in geomagnetic coordinates. Most recent simulations for the three latitudes provided by the NCAR thermosphere/ionosphere/mesosphere electrodynamics general circulation model are compared to the observations. The results at low- and mid-latitudes agree well with the observed winds in both wind structures and magnitudes, and reveal details of wave transition. Simulations for high-latitudes are less satisfactory, and require further improvements. |
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