Sensitivity of near-surface atmospheric circulation to tropical instability waves

Abstract

A set of atmospheric general circulation model experiments were performed where the Community Atmospheric Model version 3.1 is forced with sea-surface temperatures (SSTs) that have the imprint of tropical instability waves (TIWs) of varying strengths. The presence of TIWs in the SSTs increased the variance in the large-scale circulation in the atmospheric boundary layer (ABL). The impact of TIWs in the SST anomalies is directly seen in enhanced mixing of the air temperature anomalies, thereby diffusing the air temperature gradients setup by the oceanic fronts throughout the ABL. The presence of TIWs transformed the diffusive-natured ABL to advection-dominated regime. This implies that within the ABL, the presence of TIWs leads to the enhanced interactions among the neighboring grid cells and prompts greater horizontal communications among atmospheric variables. However, the advection in the ABL due to the TIWs is not a linear function of increasing TIW strength. Unlike air temperature, zonal, and vertical velocity, the variance in the meridional velocity changes at the top of the ABL due to the momentum mixing across the ABL in the vertical direction. This causes the ABL to be more turbulent beyond seasonal time scales. This analysis also suggests that a simple parameterization is not sufficient to take the account of rectification effects on the atmospheric variables that are missing due to the lack of TIW representation in the coarse-resolution coupled general circulation models.