Multiple and spin off initiation of atmospheric convectively coupled Kelvin waves

A novel atmospheric convectively coupled Kelvin wave trajectories database, derived from Tropical Rainfall Measuring Mission precipitation data, is used to investigate initiation of sequential Kelvin wave events. Based on the analysis of beginnings of trajectories from years 1998–2012 it is shown that sequential event initiations can be divided into two distinct categories: multiple initiations and spin off initiations, both of which involve interactions with ocean surface and upper ocean temperature variability. The results of composite analysis of the 83 multiple Kelvin wave initiations show that the local thermodynamic forcing related to the diurnal sea surface temperature variability is responsible for sequential Kelvin wave development. The composite analysis of 91 spin off Kelvin wave initiations shows that the dynamic forcing is a dominant effect and the local thermodynamic forcing is secondary. Detail case studies of both multiple and spin off initiations confirm statistical analysis. A multiple initiation occurs in the presence of the high upper ocean diurnal cycle and a spin off initiation results from both dynamic and local thermodynamic processes. The dynamic forcing is related to increased wind speed and latent heat flux likely associated with an off equatorial circulation. In addition a theoretical study of the sequential Kelvin waves is performed using a shallow water model. Finally, conceptual models of these two types of initiations are proposed.