Simulation of chemical transport by Typhoon Mireille (1991)

This study examines the transport of chemical species to the upper troposphere/lower stratosphere (UTLS) by Typhoon Mireille (1991). We follow an integrated research approach, using in situ flight data when available and results from a high-resolution chemical transport model. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) was used with an innermost grid spacing of 3 km to explicitly resolve the convection being studied. Mireille was well simulated based on comparisons between the simulated fields and in situ chemical measurements from NASA's Pacific Exploratory Mission-West A field project. Results from the simulated fields show that pollution from distant sources is ingested by Mireille and subsequently lofted by eyewall convection to the upper troposphere, enhancing concentrations in this region. Flux calculations suggest that a strong tropical cyclone (TC), such as Mireille, can impact UTLS chemistry as much as a continental middle-latitude cyclone. Furthermore, overshooting convective cells in Mireille produced values of chemical flux density at tropopause level that are as much as 15-30 times greater than that of theTC as a whole. Although overshooting tops comprise only a small area of the simulated total TC, they transport large quantities of gaseous species to the upper troposphere because of their strong updrafts.