89th American Meteorological Society Annual Meeting

Tuesday, 13 January 2009
Potential contributions of Tropical Instability Waves in change of eastern equatorial Pacific's climate
Hall 5 (Phoenix Convention Center)
Balachandrudu Narapusetty, George Mason University, Calverton, MD; and B. P. Kirtman
In eastern equatorial Pacific, so-called tropical instability waves (TIWs) potentially alter sea surface temperature (SST) and atmospheric boundary layer (ABL) interactions to produce significant shifts in low-level circulation. The non-linear rectification effects by TIWs impact the low-level circulation on intraseasonal and interannual time scales. Some proposed hypotheses explain qualitatively what may be the effects of TIWs on tropical climate, however SST-ABL interactions on intra-seasonal time scales have to be demonstrated using general circulation models (GCMs).

In this study we examine the TIWs effect on SST-ABL coupling in the eastern equatorial region, in the wake of TIW-induced SST modulations on El Niņo, La niņa and normal composite years. We extract daily TIWs from the respective composite years from advanced very high resolution radiometer (AVHRR) derived data using a spectral method and use this data to drive a low (T42: 2.8o horizontal) and a modrate (T85: 1.4o horizontal) resolution atmospheric GCM (AGCM; Community Atmosphere Model (CAM 3.1)) in conjunction with climatological sea surface temperatures.

Preliminary results show low-level circulation of CAM even on T42 resolution is sensitive to imposed daily TIWs and the quantities of key meteorological variable' changes are in reasonable agreement with that of ideal AGCM-TIW studies.

Performed AGCM sensitivity experiments driven by ideal TIWs varying in space and time in association with varying the strengths of extracted TIWs from fine resolution SST observational datasets underscores the importance of non-linear rectification effect of TIWs. TIWs estimated from El Niņo, La Niņa, and neutral years of AVHRR SST derived datasets are shown to influence low-level circulation differently even on low-resolution AGCMs.

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