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Intraseasonal Variability in Tropical Mean Temperature and Precipitation and Their Relation to the Tropical 40–50 Day Oscillation

Christian H. BantzerDepartment of Atmospheric Sciences, University of Washington, Seattle, Washington

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John M. WallaceDepartment of Atmospheric Sciences, University of Washington, Seattle, Washington

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Abstract

Intraseasonal variability of tropical mean tropospheric temperature and precipitation are investigated using newly available gridded datasets from the satellite-based microwave sounding unit (MSU). Lag regression and cross-spectrum analysis reveal a strong, dynamically consistent, zonally symmetric component of the tropical 40–50 day oscillation. A fast eastward propagating signal is found in upper-tropospheric temperature and zonal wind, emanating, from the region of enhanced precipitation associated with the 40–50 day oscillation. The temperature signal is consistent with an interpretation in terms of the transient tropospheric response to the switch-on of an equatorial heat source, in the form of a Kelvin wave front, and a recently detected very fast (˜40 m s−1) tropical tropospheric signal, with a vertical structure suggestive of the first baroclinic mode. Such fast moving wave fronts are hypothesized to be instrumental in maintaining the observed high degree of homogeneity in tropical temperature fields by effectively redistributing the warming generated by latent heat released in regional convective systems over the entire Tropics.

Abstract

Intraseasonal variability of tropical mean tropospheric temperature and precipitation are investigated using newly available gridded datasets from the satellite-based microwave sounding unit (MSU). Lag regression and cross-spectrum analysis reveal a strong, dynamically consistent, zonally symmetric component of the tropical 40–50 day oscillation. A fast eastward propagating signal is found in upper-tropospheric temperature and zonal wind, emanating, from the region of enhanced precipitation associated with the 40–50 day oscillation. The temperature signal is consistent with an interpretation in terms of the transient tropospheric response to the switch-on of an equatorial heat source, in the form of a Kelvin wave front, and a recently detected very fast (˜40 m s−1) tropical tropospheric signal, with a vertical structure suggestive of the first baroclinic mode. Such fast moving wave fronts are hypothesized to be instrumental in maintaining the observed high degree of homogeneity in tropical temperature fields by effectively redistributing the warming generated by latent heat released in regional convective systems over the entire Tropics.

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