Monday, 24 March 2003
The 1997/98 El Niņo Cloud Properties from SAGE II
The present study examines the cloud properties during the peak of the 1997/98 El Nino in relation to climatological conditions, based on measurements from the second Stratospheric Aerosol and Gas Experiment (SAGE II). Using the solar occultation technique, the SAGE II satellite instrument is capable of providing measurements with a 1-km vertical resolution facilitating the analysis with sufficient vertical as well as global scale (70S-70N) details. The results from the present study of the cloud distribution indicate: (1) above normal high-altitude opaque cloud occurrence over the eastern tropical Pacific and an opposite situation over the Pacific warm pool, leading to a global distribution of the cumulative opaque cloud anomalies at 3 km consistent with the pattern of observed tropical sea surface temperature and precipitation anomalies; (2) a similar behavior in the subvisual cloud distributions near the tropical tropopause; and (3) a zonally averaged cloud distribution that is characterized by reduced opaque clouds at low latitudes, except in the sourthern Tropics below 10 km, and enhanced opaque clouds poleward of 60 deg, along with increased subvisual clouds in the southern Tropics and decreased subvisual clouds in the northern subtropics in the upper troposphere. A discussion on the influence of the El Nino on large-scale mean tropospheric circulations is also provided. The present study demonstrates the capability of the solar occultation technique for measuring near global cloud vertical distribution under extreme climate conditions. The observed distinct cloud anomalies during this unusual 1997/98 El Nino constitute a unique dataset for validating and improving cloud-climate interactions in general circulation and climate models.
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