ESRL/PSD Seminar Series
Interactions between the ITCZ and Convectively Coupled Kelvin Waves
CIRES Postdoc, NOAA PSD
A number of studies have shown that Convectively Coupled Kelvin Waves (CCKWs) are strongly affected by the interactions among atmospheric circulation, moisture transport, and deep convection. In particular, observations show that enhanced Kelvin wave activity in the central Pacific Inter Tropical Convergence Zone (ITCZ) is associated with intensified eastward-propagating convective activity. In this presentation, the physical mechanisms of the interactions between the ITCZ and CCKWs are investigated using a simple model based upon the quasi-equilibrium concept, and through analysis of brightness temperature data. The idealized model for the tropical atmosphere is used to derive an analytical relation between the propagation speed of CCKWs and the location and width of the ITCZ. This relationship highlights several key features of the modeled CCKWs that are consistent with the observed CCKWs, including weak dispersion and meridional circulation. It is argued that the latter is necessary to have a coherent structure propagating eastwards along the ITCZ, which favors convergence and therefore enhances precipitation within the ITCZ. These modeling results suggest a robust dynamical modulation of the CCKWs through the ITCZ, and data analysis reveals several aspects of these interdependencies. For instance, a statistical analysis suggests that, consistently with the theoretical results, the fastest waves are found when the ITCZ is the furthest from the equator and the narrowest. Conversely, the slowest waves are more likely observed along broad ITCZs that are located near the equator.
Wednesday, November 3rd
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