Atmospheric response to SST anomalies. Part I: Background-state dependence, teleconnections, and local effects in winter

Abstract

The atmospheric response to SST anomalies is notoriously difficult to simulate and may be sensitive to model details and biases, particularly in midlatitudes. Studies have suggested that the response is particularly sensitive to a model's background wind field and its variability. The dependence on such factors has meant that it is difficult to know what responses, if any, are robust, and whether the system itself is sensitive or whether models themselves are failing. Our goal in this work is to better understand the geographical and seasonal dependence of the atmospheric response to SST anomalies, with particular attention to the role of the background state. We examine the response of an idealized atmospheric model to SST anomalies using two slightly different configurations of continents and topography. These configurations give rise to different background wind fields and variability within the same season and therefore give a measure of how robust a response is to small changes in the background state. We find that many of the midlatitude SST anomalies considered do not produce responses that are common across our model configurations, confirming that this problem is very sensitive to the background state. Local responses in the tropics, however, are much more robust. Some of the basic-state dependence seen in midlatitudes appears to be related to the structure of both the model's modes of internal variability and the stationary wave field. In addition, midlatitude responses involving a significant amount of vertical temperature advection produce larger-scale responses, consistent with recent studies of atmospheric responses near strong western boundary currents.