Patterns of North Atlantic Strom Track in the Upper and Lower Troposphere and Their Eddy Kinetic Energy Analysis

This study investigates the distribution of the North Atlantic Storm Track (NAST) in the upper and lower troposphere, and associated eddy kinetic energy (EKE) distribution in each layer. EKE is then isolated in each layer. The results shows that there is a great difference in NAST and EKE between the upper and lower troposphere. In the upper troposphere, the NAST stays a bit further southwest; in the lower troposphere, the NAST shifts poleward. By examining each term in the EKE equation, it is found that the barotropic conversion is opposite in the two layers, which could be responsible for the great difference in their storm track distribution patterns. That is to say, the barotropic conversion mainly damps EKE in the upper layer whereas it strengthens EKE in the lower layer because the barotropic conversion is negative in the upper layer but positive and shows the maximum value in the center of NAST in the lower layer. Furthermore, the baroclinic conversion and the ageostrophic geopotential flux divergence both contribute to the maintenance of EKE in the upper layer.