Impacts of convectively coupled kelvinwaves on environmental conditions for Atlantic tropical cyclogenesis

Abstract

High-amplitude convectively coupled equatorial atmospheric Kelvin waves (CCKWs) are explored over the tropicalAtlantic during the boreal summer (1989-2009). Focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis. CCKWs are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it. This dynamical signature increases vertical wind shear over the western tropical Atlantic ahead of the convectively active phase, and reduces vertical wind shear after its passage. The opposite is true over the eastern tropical Atlantic where the climatological vertical wind shear is easterly. Positive total column water vapor (TCWV) anomalies progress eastward with the convectively active phase of the CCKW, whereas negative TCWVanomalies progress eastward with the convectively suppressed phase. During the passage of the convectively active phase of the CCKW, a zonally oriented strip of low-level cyclonic relative vorticity is generated over the tropical Atlantic. Two days later, this strip becomes more wavelike and moves back toward the west. This signature resembles a train of westward-moving easterly waves and suggests CCKWs may inuence such events. Strong CCKWs over the tropicalAtlantic tend to occur during the decay of the active convection associated with the Madden-Julian oscillation over the Pacic. This relationship could be used to provide better long-range forecasts of tropical convective patterns and Atlantic tropical cyclogenesis. © 2012 American Meteorological Society.