"Understanding our global environment and our role
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Reports to the Nation:
Our Changing Planet
What controls the seasonal and interannual variations of
precipitation in tropical South America?
- A combined observational and
climate model study of
ocean-atmosphere-land coupling for improving climate prediction
School of Earth and Atmospheric Sciences, Georgia Institute of Technology
| With support from a previous PACS grant, we have
comprehensively documented convection and the atmospheric
thermodynamic structure on seasonal and diurnal scales for
tropical South America. For example, we have discovered that the
expected austral spring rainy season is suppressed by an inversion
and dryness in the lower troposphere in the eastern basin. Hence
the rainy season only appears once a year in austral fall,
compared to twice a year in the western basin. This different
seasonality between the east and west appears to be influenced by
the difference in the annual changes of sea surface temperatures
(SSTs) between the eastern Pacific and Atlantic. Based on these
findings, the future research proposed here will focus more
closely on the following questions:
a) How do the SSTs in the southeastern Pacific and south Atlantic affect the lower troposphere humidity and static stability in the western and eastern equatorial South America? b) How do boundary layer temperature, humidity and clouds in the morning affect the onset of afternoon deep convection? How do changes in day-time and nocturnal precipitation contribute to the seasonal and interannual variations of precipitation? d) Why do climate models simulate a semi-annual, rather than the observed annual cycle, for equatorial eastern Amazon? What causes the inadequate simulations of the lower tropospheric thermodynamic structure, especially with regards the inversion? To address a), we will analyze the assimilated atmospheric thermal and dynamic fields and radiosonde data, satellite and ground-based cloud and precipitation observations, and satellite observations of surface latent flux over the Atlantic Ocean. In addition to monthly means, daily to 5-day resolutions will be used to examine the responses of the atmosphere to the changes of the land and ocean surface conditions prior to the onset of the wet season. Simulations of a climate model, such as the National Center For Atmospheric Research (NCAR) Climate System Model (CSM), will be used to isolate the effects of SSTs in the adjacent oceans. We will examine b) in detail by combining the satellite data of meso-scale convective systems and ground-based cloud observations, with hourly data of surface fluxes and meteorological variables from past and future field experiments. Simulations of a boundary layer model will be used to test the effects of surface fluxes and boundary layer clouds on the occurrence of afternoon convection. We will address c) by comparing CSM simulations with radiosonde, satellite clouds and precipitation, and assimilated data. CONTACTS Principal Investigator: Rong Fu Co-Investigator: Robert E. Dickinson INSTITUTION: School of Earth and Atmospheric Sciences Return to CLIVAR PACS Home Page |
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