Daniel Phoenix Oct-2

Name:     Daniel Phoenix

Title:    Simulated Impacts of Tropopause-Penetrating Convection on the Chemical Composition of the Upper Troposphere and Lower Stratosphere

Location: NWC 5930

Date:     2019/10/2

Time:     03:00 PM

Series:   Weather and Climate Systems

Abstract: Tropopause-penetrating convection is capable of rapidly transporting air from the lower troposphere to the upper troposphere and lower stratosphere (UTLS). Since the vertical redistribution of gases in the atmosphere by convection can have important impacts on the chemistry of the UTLS, the radiative budget, and climate, it has become a recent focus of observational and modeling studies. Despite being otherwise limited in space and time, recent aircraft observations from field campaigns such as the Deep Convective Clouds and Chemistry (DC3) experiment have provided new high-resolution observations of convective transport. Modeling studies, on the other hand, offer the advantage of providing high-resolution spatially and temporally continuous output related to the physical, dynamical, and chemical characteristics of storms and their environments.

To examine the impact of tropopause-penetrating convection on the chemical composition of the UTLS, two 10-day periods of high frequency, tropopause-penetrating convection over the United States were simulated using the Weather Research and Forecasting model with Chemistry (WRF-Chem). One period representative of springtime convection (May 18-27, 2011) and one period representative of summertime convection (August 5-15, 2013) were chosen to examine the differences in convective transport between the two seasons. Overall, springtime convection has a larger impact than summertime convection, with a net effect of increasing water vapor in the lower stratosphere and increasing ozone in the upper troposphere. Springtime convection frequently increases the water vapor mixing ratio in the lowermost stratosphere by over 20% while changes in stratospheric water vapor from summertime convection are much lower (~7-11% increase). Increases in the upper tropospheric ozone mixing ratio range from

8-19% from springtime convection and are minimal from summertime convection. Changes in the composition of the UTLS are largely sensitive to the height of the tropopause, with the largest changes being in environments with tropopause heights between 11 and 13 km (typical of springtime environments in the United States). An objective algorithm to detect stratosphere-to-troposphere transport of ozone-rich air shows that while this air occasionally descends in the troposphere around the anvil of convective storms, the air is rarely of stratospheric origin. The algorithm suggests that large springtime convective systems in low-tropopause environments are most responsible for this downward transport.