Equatorial modes observed in atmospheric variables |
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Authors: | L Kiranmayi G S Bhat |
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Institution: | (1) Global Modeling and Assimilation Office, NASA/Goddard Space Flight Center, Mail Code 610.1, Greenbelt, MD 20771, USA;(2) School of Ocean and Earth Science and Technology, International Pacific Research Center, University of Hawaii at Manoa, Honolulu, HI 96822, USA |
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Abstract: | Wavenumber-frequency spectral analysis of different atmospheric variables has been carried out using 25 years of data. The
area considered is the tropical belt 25°S–25°N. A combined FFT-wavelet analysis method has been used for this purpose. Variables
considered are outgoing long-wave radiation (OLR), 850 hPa divergence, zonal and meridional winds at 850, 500 and 200 hPa
levels, sea level pressure and 850 hPa geopotential height. It is shown that the spectra of different variables have some
common properties, but each variable also has few features different from the rest. While Kelvin mode is prominent in OLR
and zonal winds, it is not clearly observed in pressure and geopotential height fields; the latter two have a dominant wavenumber
zero mode not seen in other variables except in meridional wind at 200 hPa and 850 hPa divergences. Different dominant modes
in the tropics show significant variations on sub-seasonal time scales. |
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Keywords: | |
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