Extended Abstract (984K)5.7
A study of tropical instability waves over the Atlantic using a coupled regional atmosphere–ocean model
Jen-Shan Hsieh, Department of Oceanography, Texas A & M University, College Station, TX; and P. Chang and R. Savaranan
The tropical instability waves with wavelengths of about 1000 km and periods between 25 and 40 days are frequently observed in the tropical regions of the Pacific and the Atlantic oceans. The generation of these waves trapped within the atmospheric boundary layer has been considered a direct response of the atmosphere to the SST variations, resulting from advection of the SST front by instabilities of the near-surface equatorial ocean currents. Some previous numerical studies also indicate that such ocean instability waves are controlled to some extent by surface wind forcing, suggesting a feedback from the atmosphere to the ocean instability waves.
A regional climate model forced by observed daily SST over the Atlantic has demonstrated the ability to realistically capture the tropical instability waves in the atmosphere, induced by SST perturbations due to the corresponding ocean instability waves. Preliminary results has shown that these instability waves over the Atlantic can cause some remote climate effects over the west coast of Africa and the tropical Atlantic, i.e. intraseasonal variation of the ITCZ precipitation. These waves not only contribute to the climate variability over the Atlantic but also are influenced by it. For example, tropical instability waves tend to be less active under El Nino condition and more active during La Ninas. A regional climate model has been coupled with a reduced gravity ocean model to explore the ocean-atmosphere coupling mechanism for these waves. A comparison between the waves forced by observed daily SST and air-sea interaction may help uncover the ocean-atmosphere coupling effect on the properties of tropical instability waves. To further investigate how the atmosphere interacts with the ocean through the generations of these equatorial instability waves, a detailed diagnosis of these modeled waves, such as the dispersion relation and the energetics of these instability waves, will be conducted to study the main mechanisms responsible for the generation and maintenance of these waves in the lower troposphere.
Session 5, Comparisons between high-resolution regional and global models for studying climate
Thursday, 18 January 2007, 1:30 PM-4:30 PM, 206B
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