A Composite Analysis of the Environmental Memory of Tropical Cyclones

An important focus of ongoing research in tropical meteorology is why there are, on average, 90 tropical cyclones (TCs) globally per year and how this number may vary in response to climate change. Greater understanding of current and future trends in TC activity may be achieved by determining whether TCs have a substantial impact upon the climate. While the potential climate role of TCs remains undefined, prior research suggests that TCs may cool and dry their atmospheric environment for several weeks following TC passage. Building upon prior work, the present study seeks to refine the potential climate role of TCs by examining the atmospheric thermodynamic anomalies induced by western North Pacific tropical cyclone passage using storm-relative composites.

The composite analysis reveals negative moist static energy (MSE) anomalies containing embedded westward propagating anomalies that generally only occur following larger TCs. Negative MSE anomalies occur for nearly two months following TC passage in a region extending from the domain center to ~3000 km to its west. These negative MSE anomalies are primarily composed of dry anomalies in the lower-and-midtroposphere and, to lesser extent, cool anomalies at the boundary layer and upper troposphere. Larger TCs force negative MSE anomalies due to feedbacks from stronger, broader TC-induced negative sea surface temperature anomalies and the excitation of TC-induced Rossby waves to the southeast of the TC. These results conservatively suggest that larger TCs can anomalously cool and dry their synoptic-scale environment for ~40 days following TC passage.