HR: 11:05h
AN: GC12A-04    [Abstracts]
TI: Changes of cloudiness over tropical land during the past few decades and its link to global climate change
AU: * Arias, P
EM: paola.arias@eas.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Drive, Earth and Atmospheric Sciences, Atlanta, GA 30329, United States
AU: Fu, R
EM: rf66@mail.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Drive, Earth and Atmospheric Sciences, Atlanta, GA 30329, United States
AU: Li, W
EM: wenhong@eas.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Drive, Earth and Atmospheric Sciences, Atlanta, GA 30329, United States
AB: Tropical forests play a key role in determining the global carbon-climate feedback in the 21st century. Changes in rainforest growth and mortality rates, especially in the deep and least perturbed forest areas, have been consistently observed across global tropics in recent years. Understanding the underlying causes of these changes, especially their links to the global climate change, is especially important in determining the future of the tropical rainforests in the 21st century. Previous studies have mostly focus on the potential influences from elevated atmospheric CO2 and increasing surface temperature. Because the rainforests in wet tropical region is often light limited, we explore whether cloudiness have changed, if so, whether it is consistent with that expected from changes in forest growth rate. We will report our observational analysis examining the trends in annual average shortwave (SW) downwelling radiation, total cloud cover, and cumulus cover over the tropical land regions and to link them with trends in convective available potencial energy (CAPE). ISCCP data and radiosonde records available from the Department of Atmospheric Sciences of the University of Wyoming (http://www.weather.uwyo.edu/upperair/sounding.html) are used to study the trends. The period for the trend analysis is 1984-2004 for the ISCCP data and 1980-2006 for the radiosondes. The results for the Amazon rainforest region suggest a decreasing trend in total cloud and convective cloud covers, which results in an increase in downwelling SW radiation at the surface. These changes of total and convective clouds are consistent with a trend of decreasing CAPE and an elevated Level of Free Convection (LFC) height, as obtained from the radiosondes. All the above mentioned trends are statistically significant based on the Mann-Kendall test with 95% of confidence. These results consistently suggest the downward surface solar radiation has been increasing since 1984, result from a decrease of convective and total cloudiness over the Southern Amazon basin, due to an increase of LFC and atmospheric thermodynamic stability. Such an increase of surface SW radiation probably has contributed to the increasing in growth rate for the forests in the Amazon forests. Currently, the same analysis is being applied using radiosonde data from the Comprehensive Aerological Reference Data Set (CARDS) over the Amazon and Congo basins and the Southeast Asia. Our objective is to identify changes in cloudiness over tropical land and identify its underlying causes, especially the link to changes in surface temperature and humidity.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1637 Regional climate change
DE: 1699 General or miscellaneous
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting