Tropopause‐overshooting convection transports air from the lower troposphere to the upper troposphere and lower stratosphere (UTLS) where the resulting chemistry and mixing of trace gases can modify the radiation budget. While recent work has examined output from model simulations as well as aircraft and satellite observations of the impacts of tropopause‐overshooting convection on UTLS composition, the range of potential impacts and their dependence on characteristics of storms and their environments is not known. Here, two 10‐day periods, one representative of springtime convection and one representative of summertime convection, were simulated with the Weather Research and Forecasting (WRF) model with Chemistry to examine the range of UTLS composition impacts from tropopause‐overshooting convection. Overall, springtime convection has a larger impact on UTLS composition than summertime convection, with a net effect of increasing water vapor (H2O) in the lower stratosphere and increasing ozone (O3) in the upper troposphere. Springtime convection frequently increases the domain average H2O mixing ratio in the lowermost stratosphere by over 20% while changes in stratospheric H2O from summertime convection are much lower (∼7%–11% increase), reflecting a dependence of the maximum possible H2O increase on UTLS temperature. Increases in upper troposphere O3mixing ratios span the range 8%–19% from springtime convection and are minimal from summertime convection. Changes in the composition of the UTLS from tropopause‐overshooting convection are largely dependent on the height and temperature of the tropopause, with the largest changes being in environments with relatively low tropopause heights between 11 and 13 km (typical of springtime environments in the United States).
Recent observational studies have shown that stratospheric air rich in ozone (O3) is capable of being transported into the upper troposphere in association with tropopause‐penetrating convection (anvil wrapping). This finding challenges the current understanding of upper tropospheric sources of O3, which is traditionally thought to come from thunderstorm outflows where lightning‐generated nitrogen oxides facilitate O3formation. Since tropospheric O3is an important greenhouse gas and the frequency and strength of tropopause‐penetrating storms may change in a changing climate, it is important to understand the mechanisms driving this transport process so that it can be better represented in chemistry‐climate models. Simulations of a mesoscale convective system (MCS) around which this transport process was observed are performed using the Weather Research and Forecasting model coupled with Chemistry. The Weather Research and Forecasting model coupled with Chemistry model adequately simulates anvil wrapping of ozone‐rich air. Possible mechanisms that influence the transport, including small‐scale static and dynamic instabilities and MCS‐induced mesoscale circulations, are evaluated. Model results suggest that anvil wrapping is a two‐step transport process (1) compensating subsidence surrounding the MCS, which is driven by mass conservation as the MCS transports tropospheric air into the upper troposphere and lower stratosphere, followed by (2) differential advection beneath the core of the MCS upper‐tropospheric outflow jet which wraps high O3air around and under the MCS cloud anvil. Static and dynamic instabilities are not a leading contributor to this transport process. Continued fine‐scale modeling of these events is needed to fully represent the stratosphere‐to‐troposphere transport process.more » « less
- NSF-PAR ID:
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- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Medium: X
- Sponsoring Org:
- National Science Foundation
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