An examination of summertime cyclone transport processes during Intercontinental Chemical Transport Experiment (INTEX-A)

Abstract

Warm conveyor belts (WCBs) are important mechanisms for transporting pollution during the cool season. These airstreams distribute surface emissions throughout the troposphere, playing a major role in the long-range transport of chemical species. Previous efforts to understand the lofting of WCBs have not investigated the relative importance of vertical forcing. In this study, we use fine resolution model-derived meteorological data, air parcel trajectories, flux calculations, and a diagnostic package for weather systems to perform a focused investigation of WCBs during the warm season INTEX-A period. Lifting and transport mechanisms during INTEX-A are compared to a well-documented cool season WCB case in the literature. Results show that weak, midlatitude cyclones are capable of producing vertical transport as great or greater than much stronger cyclones. An analysis of forcing terms contributing to vertical motion reveals that the Laplacian of latent heat release is the primary contributor to vertical motion during some cases of INTEX-A. The latent heating term is found to be greatest in areas of deep convection. This convection allows weak cyclones to produce WCB-like transport. WCB pathways are similar for the cases studied. In each example, air which originates far south of the low in the warm sector ascends to the north and joins the upper level westerly flow northeast of the low center. Although the transport pathways are similar, the forcing mechanism and location of maximum vertical transport are found to exhibit strong case-to-case variability. When cyclone-scale dynamics are relatively weak, widespread deep convection, especially south of the cyclone's center, is necessary to produce transport resembling a WCB. Copyright 2006 by the American Geophysical Union.