Evaluating the relationship between large-scale and storm-ambient environments

Ultimately tropical cyclones are sensitive to the environmental conditions in their local –or storm ambient– environment. However, the assumption that large-scale (basin averaged) fields, like vertical wind shear or sea surface temperature (SST), are a good proxy for storm ambient conditions is implicit in various studies regarding tropical cyclone activity and climate. Furthermore, recent work has shown that small shifts in Atlantic storm track can change, for example, storm ambient SST an equivalent amount, as will interannual to decadal changes in the mean state over the so-called Main Development Region (MDR). We test the assumption that regionally averaged fields are a good proxy for storm ambient conditions during the 1983 Atlantic hurricane season, a year of exceptionally weak Atlantic tropical cyclone activity. We manually track more than 60 disturbances across the MDR that have African Easterly Wave-like features and use the NASA-GMAO Modern Era Retrospective-analysis for Research and Applications (MERRA) reanalysis to quantify the differences and similarities between storm (or disturbance)-ambient conditions and those averaged over the broader MDR. Our results suggest that MDR averaged fields are not always a good proxy for the environment that tropical cyclones experience, and that by examining the disturbance-ambient environment we are able to gain new insight into the dominant factors that contributed to the exceptionally low numbers of tropical cyclones that formed in the Atlantic in 1983.