Predominant semi-annual oscillation of the upper mesospheric airglow intensities and temperatures in the equatorial region |
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| Institution: | 1. NASA Goddard Space Flight Center, Code 695, 8800 Greenbelt Rd., Greenbelt, MD 20771, USA;2. Space Telescope Science Institution, 3700 San Martin Dr., Baltimore, MD 21218, USA;1. Department of Physics, S.V. University, Tirupati, Andhra Pradesh, India;2. Department of Earth System Science, University of California, 3226 Croul Hall Irvine, CA 92627-3100, USA;3. Institute Center for Water and Environment (iWATER), Masdar Institute of Science and Technology, P.O. Box 54224, Abu Dhabi, United Arab Emirates;1. Equatorial Geophysical Research Laboratory, Krishnapuram, Tirunelveli, 627011, India;2. National Atmospheric Research Laboratory, Gadanki, Tirupati, 510112, India;3. Indian Institute of Geomagnetism, New Panvel, Navi Mumbai, 410218, India |
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| Abstract: | The upper mesospheric and lower thermospheric airglow emissions, OI 557.7 nm, NaD 589.3 mn and the OH (9,4) band and its rotational temperature have been measured using a ground-based multichannel airglow photometer located at Fortaleza (3.9°S, 38.4°W) since 1986. The observed emission intensities show predominantly semi-annual oscillations with maxima at the equinoxes and minima during the solstices. The amplitudes of the oscillations are larger than those observed from the low latitude station, Cachoeira Paulista (22.7°S, 45.0°W). The OH rotational temperature, which represents a gas kinetic atmospheric temperature at around 85–95 km, also shows a strong semi-annual oscillation, 18 K peak to peak, with an. average value around 10 K higher than that observed from Cachoeira Paulista. These results do not agree with model atmospheres presently available. It is suggested that the differences result from the effects of seasonal variations in vertical eddy transport and/or meridional circulation. |
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