Long-range stratospheric ozone contribution to the troposphere during INTEX

Globally assimilated stratospheric ozone from the Regional Air Quality Modeling System (RAQMS UW hybrid component) is used to initialize the high resolution regional model component (University of Wisconsin Nonhydrostatic Modeling System or UWNMS) to quantify the contribution of ozone flux across the tropopause to tropospheric ozone traveling across the Pacific to the United States during the Intercontinental Chemical Transport Experiment (INTEX) in 2004. The two-scale method of Buker et al. (2005) allows quantification of irreversible and reversible stratosphere/troposphere exchange (STE) of ozone. The contribution of stratospheric ozone is treated with a separate conserved ozone tracer.

The focus is on two distinct transport paradigms: classical tropopause folding associated with Rossby wave breaking (RWB), and tropopause folding associated with convective complexes. Simulations performed on the UWNMS reveal detailed distributions of ozone flux (both into and out of the stratosphere) in the vicinity of a large, quasi-stable RWB feature upstream of North America. RWB is useful as an indicator for the general region for STE; however, the largest magnitudes tended to be found near intense shortwaves traveling well north of the large meridional PV reversal. Differences in the definition of the tropopause and grid resolution from other studies results in a significantly different picture of STE in this 'classical' RWB pattern. Long-range stratospheric influence due to convection is illustrated in a second case study, where a convective complex on July 2-3 over the central north Pacific contributed significant ozone to the troposphere, which accounted for more than 10% of the modeled background ozone on July 6 over the western U.S. during the INTEX transit flight.