A new approach to the observations of equatorial thermospheric dynamics

Details A new approach to the observations of equatorial thermospheric dynamics A new approach to the observations of equatorial thermospheric dynamics

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa43a..04f&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA43A-04

Physics

3369 Thermospheric Dynamics (0358), 3394 Instruments And Techniques

Scientific paper

The Arequipa Fabry-Perot interferometer (FPI) (16.5 ° S, 71.57 ° W) was recently upgraded with a bare CCD camera. This observatory located 4 degrees south of the magnetic equator operated automatically for nights between late March to mid-October 2005. The new results for the O1D 630-nm Doppler shifts and Doppler widths show uncertainties of ~5 ms-1 and ~20 K for 240 s exposures. A new observation mode was started in early June in which 8 azimuthal directions are sampled every 45° with respect to north with a zenith angle of 60° and 120 s exposures. The radius of this circle for the FPI line-of-sight view at the height of ~250 km is about 800 km. This approach was used two decades ago by Burnside to map the effect of the midnight temperature maximum (MTM) dynamics on the horizontal wind field. The wind vector is expanded in a Taylor series relative to the zenith of the observation site. The analysis procedure retrieves the partial derivatives of the zonal and meridional wind components by using a Fourier decomposition of the line-of-sight speed for the 8 azimuthal directions. Numerous midnight temperature maximum (MTM) events occurring between May and September with typical temperature enhancements of 50 to 150 K as compared with the NRL MSIS-00 model reference have been studied with this new strategy, and a number of interesting findings have emerged. Determination of the meridional temperature gradients has indicated, in most cases, the thermosphere to be warmer by 20-30 K toward the south at the time of the MTM peak, generally seen one or two hours after midnight. An estimate of the vertical wind can be indirectly inferred from the determination of the horizontal wind divergence of the flow. During quiet nights, the vertical wind speed is generally less than 5 ms-1. During MTM activity, the vertical displacement shows greater amplitude, up to 8-10 ms-1, both upward and downward, but with no clear indication of a phase correlation with the MTM temperature peak. The two features of the abatement and reversal of the zonal and meridional wind speeds, respectively, reported by Burnside et al.[1981], are observed as the MTM moves from the northeast to the southwest.

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