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Abstract
Pressure oscillation having a periodicity of 4 to 6 days has been reported by many workers over different parts of the globe. Yanai et al. (1968) found a westward propagating wave with a 4- to 5-day period in certain regions of the tropics in the meridional component of the wind at lower tropospheric levels. Wallace & Chang (1969) found an easterly wave with a period of 4 to 5 days and also a 4-day period of planetary scale pressure fluctuation at the equator. Misra (1971) found a pressure oscillation of a 4- to 5-day period on a global scale. Misra (1972) also found a westward propagating planetary pressure wave of a 4- to 5-day period in the tropics. Madden & Julian (1972) also showed further evidence of a global 5-day pressure wave. Gupta (1972) showed a pressure oscillation having a 5-day periodicity over the region of the Siberian anticyclone.