Tropical 45 Day Oscillations during the 1979 Northern Hemisphere Summer

Abstract

Abstract Based on FGGE 1,cvel IIIb data, the structural features of 45 day perturbations over a tropical belt (15°N-15°S) during the 1979 summer are detailed. At the equator, 45 day perturbations which are primarily associated with the zonal wind components of wavenumber 1, propagate eastward (8° of longitude per day) and upward (0.7 km per day), probably indicating downward energy flux. In the Southern Hemisphere tropics (0°–15°S), the 45 day zonal mean wind perturbations propagate downward with an approximate phase speed of 0.8 km per day. In the Northern Hemisphere tropics, they are largely of standing character with the maximum amplitude (3 m s−1) near 200 mb at 15°N. There exists a strong association between monsoon activity over South Asia and changes in the intensity of the equatorial Walker circulation. When active monsoons occur over South Asia, the Walker circulation becomes stronger than usual with prominent 850 mb easterlies (200 mb easterlies) over the eastern Pacific east of the date line an...