Atmospheric Kelvin waves and Convective Variability

over the EPIC Study Region

George N. Kiladis, Aeronomy Laboratory, NOAA, Boulder, CO, 80304-3328 USA

[gkiladis@al.noaa.gov]

Katherine H. Straub, Geological and Environmental Sciences, Susquehanna University, Selinsgrove, PA, 17870-1001 USA

[straubk@susqu.edu]

` Atmospheric Kelvin waves have been shown to play an important role in modulating convective variability over the Pacific ITCZ. These convectively coupled Kelvin waves are large-scale, eastward-propagating disturbances with the dispersion characteristics of equatorially trapped shallow water Kelvin modes. The envelope of convection in these waves propagates eastward at around 15 m/s, with a horizontal scale of approximately 3000 km, and is accompanied by large-scale dynamical perturbations in the troposphere and lower stratosphere that are broadly consistent with linear equatorial wave theory.

Several Kelvin waves were observed during the EPIC 2001 field campaign which had substantial impact on convection over the study region. The structure and evolution of the events of October 2001 are analyzed using a variety of EPIC data sources along with satellite data and large scale dynamical fields from reanalysis. The Kelvin wave envelope that reached the eastern Pacific on October 9 was associated with a major convective outbreak off the southern coast of Mexico that was well observed by a variety of platforms. This wave was preceded by enhanced surface fluxes caused by a surge in the low level northeasterly trade wind field, followed by a substantial cross-equatorial flow as convection set up off the coast. Another somewhat weaker Kelvin event occurred during the following week. The large scale structure of these waves appear to show broad agreement with the mean structure of Kelvin waves from a statistical analysis of many such events in the historical record.