The seasonal cycle of Kelvin waves in the ECMWF analyses

Atmospheric dynamics in the tropical regions is dominated by unbalanced motions in response to convective processes, found to vary on many temporal scales from diurnal to inter-seasonal and inter-annual scales. The gravest wave excited by convection is the Kelvin wave and it is characteristics by eastward and upward propagation away from its convective source. As it propagates vertically, a pack of Kelvin waves experiences modulation, dissipation and wave breaking as determined by the environment it propagates through. This study focuses on the Kelvin wave seasonal cycle as observed in the tropical tropopause layer, a broad region between 100− 200 hPa with both tropospheric and stratospheric characteristics. The Kelvin wave properties are obtained by using the MODES methodology applied to the ECMWF operational analyses during 6 years of 91 model-level discretization. The methodology considers both wind and geopotential fields, and the latter are used to compute the temperature perturbations due to Kelvin waves. Dynamical properties of the Kelvin wave associated with the seasonal cycle are presented in relation to convection and the ambient winds and stability.