Retrievals of Convective Detrainment Heights Using Ground‐Based Radar Observations

Self Cite

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.

Section: Methodssupporting

confidence: 69%

“…Starzec et al. (2020) found that the LMD occurs between 4 and 5 km below the tropopause in the southern United States in May and July. Our study is based on the full warm season and is not fixed in geographic location, which could explain why this CO peak is observed higher in the UT.…”

Section: Resultsmentioning

confidence: 99%

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

Tinney

Homeyer

2021

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“…Irreversible exchange can occur through gravity wave breaking in and near the overshooting top (as previously mentioned to be critical for AACP formation), Kelvin‐Helmholtz instabilities near cloud top, and tropopause‐level shallow continuity circulations coupled with differential advection (O’Neill et al., 2021; Pan et al., 2014; Phoenix et al., 2020). Additionally, the amount of overshooting convection and cross‐tropopause transport in simulations exhibits several sensitivities to storm characteristics (e.g., mode—discrete supercell versus mesoscale convective system or MCS) and to the characteristics of the lower stratospheric environment (Bigelbach et al., 2014; Homeyer et al., 2014a; Mullendore et al., 2005; Starzec et al., 2020). An isolated supercell tends to have a larger updraft and deeper overshooting compared to alternative storms, while an MCS has a large number of weaker overshoots that can achieve greater overall transport and STE (Bigelbach et al., 2014).…”

Section: Introductionmentioning

confidence: 99%

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

Gordon

Homeyer

2022

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Tropopause‐overshooting convection in the midlatitudes rapidly transports lower troposphere air and cloud material to the upper troposphere and lower stratosphere (UTLS), with notable events resulting in the formation of above‐anvil cirrus plumes (AACPs). However, there is limited understanding of how transport driven by overshooting convection and AACP properties are modified by variations in UTLS environments, especially the extent of stratosphere‐to‐troposphere (i.e., downward) transport. Here, AACP development and UTLS transport sensitivities to lower stratosphere stability and the UTLS wind environment are evaluated. The Bryan Cloud Model is used to simulate midlatitude supercell convection and evaluate resulting UTLS composition changes within two common midlatitude thermodynamic environments: a single tropopause and a double tropopause, and two UTLS wind environments: one with a stronger stratospheric wind profile supportive of frequent gravity wave breaking and AACP development and the other with a weaker stratospheric wind profile to suppress gravity wave breaking and discourage AACP formation. Multiple passive tracers and water vapor concentrations are used to evaluate the exchange of air between the troposphere and stratosphere and transport confined to each layer. It is found that greater troposphere‐to‐stratosphere transport (TST) and stratospheric hydration occurs in storms with AACPs, while stratosphere‐to‐troposphere transport (STT) is greater in storms without AACPs. This STT is facilitated by a mechanical oscillation induced by the overshoot. AACP‐producing storms have increased downward transport of stratospheric overworld air to the lowermost stratosphere, which is enhanced within a double tropopause environment. More expansive AACPs, deeper overshoots, and greater TST also occurs in double tropopause environments.

Comparing Distributions of Overshooting Convection in HRRR Forecasts to Observations

Bissell,

Murillo,

Mullendore

2024

Overshooting convection can significantly impact the chemical and radiative properties of the upper troposphere and lower stratosphere through the transport of various chemical species. These impacts include enhancements of water vapor and ozone‐depleting halocarbons, which both have important consequences for climate change. Therefore, accurate prediction of the Earth's climate system requires convective overshooting to be included. To better understand how convective transport is represented in current state‐of‐the‐art models, approximately 75,000 individual updrafts in the central and eastern United States are analyzed from High‐Resolution Rapid Refresh (HRRR) simulations and NEXRAD radar observations during May and July 2021. Distributions of echo top potential temperatures and heights, as well as diurnal cycles of overshooting frequency, are compared to observations. These distributions show mean, median, and maximum echo tops 2–3 km lower than observations, both in absolute and tropopause‐relative space, with evidence of updrafts losing momentum too rapidly above the tropopause. Diurnal cycles show accurate times of maximum and minimum overshooting, but significant errors at model initialization and evidence that some simulated overshoots continue too late into the overnight hours. Despite these deficiencies, distributions of simulated levels of maximum detrainment show decent agreement with observations. All results, including the severe underprediction of echo top heights, persist at shorter forecast lead times. This indicates a need to improve representation of overshooting storms in weather and climate models, even those that are convection‐permitting, or introduce a transport parameterization.