A case of downstream baroclinic development over western North America

Abstract

Numerical simulations have been made of the initiation of a strong ridge-trough system over western North America and the eastern Pacific (the terminus of the Pacific storm track), with the objective of determining the extent to which downstream development contributed to its growth, and the possible influence of topography on the energetics of the storm. While a control simulation demonstrated considerable skill in reproducing the storm, a "simplified' simulation in which topography, surface heat fluxes, and latent heating were removed not only reproduced the primary features of the ridge-trough system - permitting a clearer interpretation of the factors contributing to its growth - but actually generated a stronger system, suggesting that these effects as a whole inhibited storm development. Application of an energy budget that distinguishes between energy generation via baroclinic processes and generation via the convergence of geopotential fluxes revealed that early growth of the system was dominated by flux convergence. These findings are in agreement with the results of previous studies that have shown that eddies near the downstream end of a storm track grow, at least initially, primarily through the convergence of downstream energy fluxes. -from Authors