Abstract
Wave proagation, forced by imposed tropical convective heat source over the Pacific warm pool in an atmospheric shallow water model, is studied. The background flows, maintained by steady climatological forcing, are based on 200 mb observed winds. Zonally asymmetric background state: equatorial and midlatitude Rossby waves extend meridionally through the westerly wind "duct" in the equatorial eastern Pacific (Webster and Holton, 1982). Upstream, the southern flank of the East Asian jet is found to be a turning latitude which reflects the inhibits waves propagating out of the tropics over the western Pacific. Impact of divergence is also studied by incorporating climatological divergence into the background flow. Both the background divergence and evolving forced divergence act as Rossby wave sources. As a positive vorticity masimum evolves, it interacts with the background divergence (convergence), causing the maximum to decay (amplify). Thus, the divergent wind, though small compared to the rotational wind, significantly alters the response pattern. Accurate specification of divergence may be essential for extended range weather forecasting. The sensitivity of responses to location of convective heat source is examined by varying the center of the heat source along the equator. Regardless of the location of heat source, teleconnection patterns similar to those observed by Wallace and Gutzler (1981) are found in the perturbation stream function field. The observed Pacific/North America pattern does not result from a barotropic instability of the basic state. Rather, the individual extrema of the observed pattern result from seperate synoptic scale interactions between the tropicws and midlatitudes; these interactions are enhanced by local Rossby wave source. In a two-layer model simulation designed to enhance baroclinic response, wave propagation in the lower layer is dramatically different from that in the upper layer. In addition to the westward propagating equatorial Rossby waves which are found in both layers, strong eastward propagating Kelvin waves appear in the lower layer. The Pacific/North America pattern developed in the one-layer model is weak or non-exist in the two-layer model, which implies that the pattern is characterized by the barotropic structure.
Zhang, Yuxia (1994). Effects of zonal asymmetry and divergence on upper troposheric responses to equatorial forcing. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1552153.