Observational and numerical study of Atlantic tropical instability waves
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This study uses high resolution satellite measurements from the Tropical Rainfall Measuring Mission (TRMM), Quick Scatterometer (QuikSCAT) and Special Sensor Mi?crowave Imager (SSM/I) to investigate the variability of sea surface temperature (SST), surface wind velocity, water vapor, cloud liquid water and precipitation associated with westward moving tropical instability waves (TIWs) in the Atlantic Ocean from 1998 to 2005. On interannual scales, TIWs in the Paci?c Ocean are strongest during the cold phase of El Ni? no Southern Oscillation (ENSO), when the cold tongue is most pronounced. The waves are weak during the warm phase of ENSO. A low-frequency Atlantic air-sea cou-pled mode in?uences the TIW activity in the Atlantic Ocean as ENSO does in the Pacific Ocean. The characteristics of TIWs are largely associated with the background oceano-graphic states. Coherent ocean-atmosphere patterns are shown in the Atlantic Ocean during eight years. Southeasterly trades strengthen and water vapor increases over warm SST anomalies associated with TIWs. The opposite is true over cold TIW SST anomalies. The cloud liquid water and rain response to the SST follows a very similar pattern, appearing to be roughly in phase with wind convergence and divergence in the central tropical Atlantic. The atmospheric response to the TIW SST anomalies extends north of the TIW active region, suggesting a remote response to the TIWs. The atmospheric response to the Atlantic TIWs shows interannual variability. In 1999, the rainfall response to the TIW SST anomalies is much larger than in other years, which is due to the southward movement of Atlantic ITCZ (Intertropical Convergence Zone). When the Atlantic ITCZ moves south, it is more susceptible to TIW in?uence. One regional climate model and one global climate model are applied to study the mechanism of atmospheric response to the Atlantic TIWs with daily TMI satellite SST forcing. Both models successfully simulated the wind velocity, wind convergence and pre-cipitation as observed. While the satellite observations support the vertical mixing mech-anism for the surface wind response to TIWs, both models show the pressure gradient mechanism is dominant in the Atlantic.