A 13‐year Trajectory‐Based Analysis of Convection‐Driven Changes in Upper Troposphere Lower Stratosphere Composition Over the United States

Abstract

Moist convection frequently reaches the tropopause and alters the distribution and concentration of radiatively important trace gases in the upper troposphere and lower stratosphere (UTLS), but the overall impact of convection on regional and global UTLS composition remains largely unknown. To improve understanding of convection‐driven changes in water vapor (H2O), ozone (O3), and carbon monoxide (CO) in the UTLS, this study utilizes 13 years of observations of satellite‐based trace gas profiles from the Microwave Limb Sounder (MLS) aboard the Aura satellite and convection from the operational network of ground‐based weather radars in the United States. Locations with and without convection identified via radar are matched with downstream MLS observations through three‐dimensional, kinematic forward trajectories, providing two populations of trace gas observations for analysis. These populations are further classified as belonging to extratropical or tropical environments based on the tropopause pressure at the MLS profile location. Extratropical regions are further separated by tropopause type (single or double), revealing differing impacts. Results show that convection typically moistens the UT by up to 300% and the LS by up to 100%, largely reduces O3 by up to 40%, and increases CO by up to 50%. Changes in H2O and O3 are robust, with LS O3 reduced more by convection within tropical environments, where the median concentration decrease is 34% at ∼2 km above tropopause, compared to 24% in extratropical environments. Quantification of CO changes from convection is less reliable due to differences being near the MLS measurement precision and accuracy.

Simulated Impacts of Tropopause‐Overshooting Convection on the Chemical Composition of the Upper Troposphere and Lower Stratosphere

“…The degree to which O 3 and CO are irreversibly mixed in convection is therefore uncertain and best addressed through increased observational analyses in the future. It is noted, however that the general results found here are consistent with recent observational work (e.g., Tinney & Homeyer, 2021).…”

“…For example, higher tropopause altitudes are typically colder than lower tropopause altitudes. Since the temperature of the tropopause controls the amount of H 2 O that enters the stratosphere, it would be expected for there to be a larger LS H 2 O enhancement in environments with a lower tropopause, as has been confirmed through vertical sections of many different cases with a wide range of tropopause heights (Figures S5 and S6) and by recent satellite analysis by Tinney and Homeyer (2021). Therefore, important details are hidden without this distinction.…”

Sensitivities of Cross‐Tropopause Transport in Midlatitude Overshooting Convection to the Lower Stratosphere Environment

“…Thus, exploring observations of storms, their environments, and composition changes in tropopause‐overshooting convection is warranted to confirm some of the conclusions of this study and/or expand understanding beyond the limits of the model. The simulations can be validated using observations from satellite and radar (e.g., Tinney & Homeyer, 2021), but fine‐scale observations from aircraft are especially needed. The NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign occurring in 2021 and 2022 should provide unprecedented observations of these events for future analysis.…”

“…This hydraulic jump behavior occurs downstream of the overshooting top (which acts as a topographic obstacle) near the tropopause (O’Neill et al., 2021). UTLS composition impacts from tropopause‐overshooting convection have been investigated using both aircraft observations of individual cases (Anderson et al., 2012; Fischer et al., 2003; Fromm & Servranckx, 2003; Hanisco et al., 2007; Hegglin et al., 2004; Herman et al., 2017; Homeyer et al., 2011, 2014b; Pan et al., 2014; Poulida et al., 1996; Smith et al., 2017) and more broadly from satellite observations (Randel et al., 2012; Schwartz et al., 2013; Smith et al., 2017; Tinney & Homeyer, 2021; Werner et al., 2020), revealing that water vapor in the upper troposphere and several kilometers deep in the lower stratosphere is enhanced from both detrainment and sublimation of ice and air mass transport, while STE of more passive tropospheric and stratospheric compounds (e.g., ozone and carbon monoxide) is largely confined to within 1–3 km above/below the tropopause altitude.…”

A 22‐Year Evaluation of Convection Reaching the Stratosphere Over the United States

“…Moist convection that reaches the stratosphere provides a rapid transport mechanism that can alter the composition of the upper troposphere and lower stratosphere (UTLS). Cloud material, aerosols, and trace gases in convective plumes are irreversibly delivered to the UTLS through mixing with environmental air (e.g., Anderson et al., 2012; Chagnon & Gray, 2007; Dessler & Sherwood, 2004; Fischer et al., 2003; Frey et al., 2015; Fromm & Servranckx, 2003; Gray, 2003; Hanisco et al., 2007; Hegglin et al., 2004; Herman et al., 2017; Homeyer et al., 2011; Homeyer, 2015; Homeyer, Pan, Dorsi, et al., 2014; Mullendore et al., 2005; Pan et al., 2014; Phoenix et al., 2020; Poulida et al., 1996; Randel et al., 2012; Schwartz et al., 2013; Setvák et al., 2008; Smith et al., 2017; Tang et al., 2011; Tinney & Homeyer, 2021; Wang, 2003). Modification of the vertical distributions of water vapor and ozone is a significant concern due to their potential effects on radiative forcing, which could drive climate variability and change (e.g., Forster & Shine, 1999; Lacis et al., 1990; S. Solomon et al., 2010).…”