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Abstract
The percentage of the interannual variance of cirrus clouds, explained by the variability of the El Niño Southern Oscillation (ENSO), the Quasi-biennial Oscillation (QBO) and solar activity over the tropics, is presented in this article. Analysis is focused on the eastern and western tropical Pacific Ocean, which is strongly affected by the ENSO. It is shown that over the eastern tropical Pacific Ocean, the amplitude of the ENSO in cirrus-cloud cover (CCC) is about 8.0%. The amplitude of the annual cycle is about 0.8% and the amplitudes of the QBO, solar cycle and long-term trends are the order of 1.0%, 0.1% and 0.3%, respectively. Using as an index of convective activity in the upper troposphere the vertical velocities at 300 hPa, we have calculated a vertical velocity related to cloud component. It is shown that the total contribution, from all related cloud components examined explains about 65% of the variance in cirrus clouds over the eastern Pacific and about 50% of the variance in cirrus clouds over its western part.
Acknowledgements
This study was conducted within the FP6 Integrated Project QUANTIFY (Contract No 003893-GOCE). NCEP reanalysis data were provided by NOAA/OAR/ESRL PSD, Boulder, CO, USA, from their web site at http://www.cdc.noaa.gov/. We also acknowledge the MODIS mission scientists and associated NASA personnel for the production of the data used in this research effort.