Coherent disturbances in the tropics: Climatology, vertical structure and relationship with tropical cyclones

Tropical and equatorial waves are the subject of a substantial body of literature. Several studies have documented their influence in modulating tropical cyclone activity within most ocean basins. In addition to these waves, the tropical atmosphere also contains localized coherent disturbances that have received relatively limited attention in the past. In this study, we examine the distribution and structure of coherent disturbances within the tropics with a special emphasis on the Atlantic.

Coherent disturbances are identified using isentropic potential vorticity (IPV) fields. An objective method is used to identify disturbances that are associated with closed contours of IPV, which is a criterion for ensuring trapped fluid parcels. The main issues of interest to this study are:

(1) The spatial variability of coherent disturbances within the tropics. (2) Their vertical structure. (3) Their relationship with convection. (4) Their relationship with the background environment; specifically, in the cases of the long-lived disturbances that track across the Atlantic basin. (5) Their relationship with tropical cyclogenesis.

This study is in progress and the presentation at the conference will highlight some of the key results.