Geostationary satellite data can be used to diagnose the time evolution of climatic events such as the El-Nino Southern Oscillation (ENSO) or tropical monsoon seasons. The two figures below are examples of the time series of the zonally averaged relative humidity and east-west (or u) component of the wind.

 The upper tropospheric humidity (or UTH in %) was determined using a modified version of the Soden and Bretherton (1996) technique. Dry regions are shown in red while moist regions are in blue. The large dry zone in the Southern Hemisphere during the Austral winter is influenced by the semi-permanent high pressure belt usually centered between 10-20°S latitude. In the Northern Hemisphere winter, a similar high pressure region (regionally called the "Bermuda High") also takes shape. The subtle interannual variations in the latitudinal extent, intensity, and duration of moist or dry periods are tell-tale signals of an anomalous climate event. For example, during the warm phase of ENSO, the upper troposphere is typically more moist than the cool phase of the Southern Oscillation (or La-Nina). This is apparent in the figure below during 1987 when the subtropics display higher UTH than during the strong La-Nina event of 1988.  

 The time series of the zonal mean u-wind shows similar seasonal changes as is evident in RH. In this figure, westerlies are indicated in green and blue, easterlies in yellow, orange, and red. In this figure easterlies tend to be observed in the deep tropics and the summer subtropics. Interestingly, Southern Hemisphere westerlies are quite persistent on average and do not undergo the seasonal variations as does the Northern Hemisphere. Northern Hemisphere easterlies are more intense, widespread, and of longer duration during the La-Nina period (1988). This signal appears to be well correlated with the occurence of tropical storms over the Atlantic Ocean and Carribean (see Gray 1984 Mon. Wea. Rev., 112, 1649-1668).

Last updated on: November 2, 1999