Extratropical Tropopause Transition Layer Characteristics from High-Resolution Sounding Data

Accurate determination of the tropopause is important for applications such as dynamical analysis and forecasting, radiative transfer calculations, and the diagnosis of chemical transport in the atmosphere. In this paper, we examine how well the extratropical tropopause is determined in the National Centers for Environmental Prediction (NCEP) high-resolution Global Forecast System (GFS) model analysis over the continental United States using high-resolution aircraft and radiosonde data. The GFS analyses and sounding data compare well, with r.m.s. differences of approximately 600m, which is comparable to the vertical resolution of the model. The GFS tropopause is a good proxy in areas without in situ observations, but near the subtropical jet the GFS analysis often mistakenly identifies the secondary rather than the primary tropopause. We also explore an alternative method to identify the tropopause by fitting a smoothed step-function to the static stability profile. This new approach provides a measure of the depth of the troposphere-stratosphere transition and facilitates the study of the dynamical behavior of the tropopause region. In particular, using the transition depth, we are able to identify the statistical behavior of temperature in profiles with deep or shallow tropopause transition layers

Wet scavenging of soluble gases in DC3 deep convective storms using WRF-Chem simulations and aircraft observations

We examine wet scavenging of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. We conduct high-resolution simulations with the Weather Research and Forecasting model with Chemistry (WRF-Chem) of a severe storm in Oklahoma. The model represents well the storm location, size, and structure as compared with Next Generation Weather Radar reflectivity, and simulated CO transport is consistent with aircraft observations. Scavenging efficiencies (SEs) between inflow and outflow of soluble species are calculated from aircraft measurements and model simulations. Using a simple wet scavenging scheme, we simulate the SE of each soluble species within the error bars of the observations. The simulated SEs of all species except nitric acid (HNO_3) are highly sensitive to the values specified for the fractions retained in ice when cloud water freezes. To reproduce the observations, we must assume zero ice retention for formaldehyde (CH_2O) and hydrogen peroxide (H_2O_2) and complete retention for methyl hydrogen peroxide (CH_3OOH) and sulfur dioxide (SO_2), likely to compensate for the lack of aqueous chemistry in the model. We then compare scavenging efficiencies among storms that formed in Alabama and northeast Colorado and the Oklahoma storm. Significant differences in SEs are seen among storms and species. More scavenging of HNO_3 and less removal of CH_3OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Graupel is associated with mixed-phase scavenging and lightning production of nitrogen oxides (NO_x), processes that may explain the observed differences in HNO_3 and CH_3OOH scavenging

A Case Study of Convectively Sourced Water Vapor Observed in the Overworld Stratosphere over the United States

On 27 August 2013, during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys field mission, NASA's ER2 research aircraft encountered a region of enhanced water vapor, extending over a depth of approximately 2 km and a minimum areal extent of 20,000 km(exp 2) in the stratosphere (375 K to 415 K potential temperature), south of the Great Lakes (42N, 90W). Water vapor mixing ratios in this plume, measured by the Harvard Water Vapor instrument, constitute the highest values recorded in situ at these potential temperatures and latitudes. An analysis of geostationary satellite imagery in combination with trajectory calculations links this water vapor enhancement to its source, a deep tropopausepenetrating convective storm system that developed over Minnesota 20 h prior to the aircraft plume encounter. High resolution, groundbased radar data reveal that this system was composed of multiple individual storms, each with convective turrets that extended to a maximum of ~4 km above the tropopause level for several hours. In situ water vapor data show that this storm system irreversibly delivered between 6.6 kt and 13.5 kt of water to the stratosphere. This constitutes a 2025% increase in water vapor abundance in a column extending from 115 hP to 70 hPa over the plume area. Both in situ and satellite climatologies show a high frequency of localized water vapor enhancements over the central U.S. in summer, suggesting that deep convection can contribute to the stratospheric water budget over this region and season

Effects of Scavenging, Entrainment, and Aqueous Chemistry on Peroxides and Formaldehyde in Deep Convective Outflow over the Central and Southeast U.S.

Deep convective transport of gaseous precursors to ozone (O3) and aerosols to the upper troposphere is affected by liquid- and mixed-phase scavenging, entrainment of free tropospheric air, and aqueous chemistry. The contributions of these processes are examined using aircraft measurements obtained in storm inflow and outflow during the 2012 Deep Convective Clouds and Chemistry (DC3) experiment combined with high resolution (dx <= 3 km) WRF-Chem simulations of a severe storm, an airmass storm, and a mesoscale convective system (MCS). The simulation results for the MCS suggest that formaldehyde (CH2O) is not retained in ice when cloud water freezes, in agreement with previous studies of the severe storm. By analyzing WRF-Chem trajectories, the effects of scavenging, entrainment, and aqueous chemistry on outflow mixing ratios of CH2O, methyl hydroperoxide (CH3OOH), and hydrogen peroxide (H2O2) are quantified. Liquid-phase microphysical scavenging was the dominant process reducing CH2O and H2O2 outflow mixing ratios in all three storms. Aqueous chemistry did not significantly affect outflow mixing ratios of all three species. In the severe storm and MCS, the higher than expected reductions in CH3OOH mixing ratios in the storm cores were primarily due to entrainment of low background CH3OOH. In the airmass storm, lower CH3OOH and H2O2 scavenging efficiencies (SEs) than in the MCS were partly due to entrainment of higher background CH3OOH and H2O2. Overestimated rain and hail production in WRF-Chem reduces the confidence in ice retention fraction values determined for the peroxides and CH2O

Introduction to the SPARC Reanalysis Intercomparison Project (S-RIP) and overview of the reanalysis systems

The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This paper summarizes the motivation and goals of the S-RIP activity and extensively reviews key technical aspects of the reanalysis data sets that are the focus of this activity. The special issue The SPARC Reanalysis Intercomparison Project (S-RIP) in this journal serves to collect research with relevance to the S-RIP in preparation for the publication of the planned two (interim and full) S-RIP reports

Microphysical Modeling of Water Isotopic Composition in the Asian Summer Monsoon

International audienceThe summertime Asian Monsoon (AM) is the single most important contributor to water vapor in the UTLS and overworld stratosphere. Much of that water comes from sublimating ice, but the life cycle of the condensate lofted by overshooting convection is not well understood. We report here on insights into that life cycle derived from the first in-situ measurements of water vapor isotopic composition over the Asian Monsoon. The Chicago Water Isotope Spectrometer (ChiWIS) flew on high-altitude aircraft in the monsoon center during the StratoClim (2017) campaign out of Nepal, and in monsoon outflow during ACCLIP (2022) out of South Korea. Both campaigns sampled a broad range of convective and post-convective conditions, letting us trace how convective ice sublimates, reforms, and leaves behind characteristic isotopic signatures. We use the Bin Resolved Isotopic Microphysical Model (BRIMM), along with TRACZILLA backtrajectories and convective interactions derived from cloud-top products, to follow the evolving isotopic composition along flight paths in both campaigns. Results support the wide diversity of isotopic enhancement seen in both campaigns and show how temperature cycles downstream of convective events progressively modify environmental isotopic compositions

Microphysical Modeling of Water Isotopic Composition in the Asian Summer Monsoon

International audienceThe summertime Asian Monsoon (AM) is the single most important contributor to water vapor in the UTLS and overworld stratosphere. Much of that water comes from sublimating ice, but the life cycle of the condensate lofted by overshooting convection is not well understood. We report here on insights into that life cycle derived from the first in-situ measurements of water vapor isotopic composition over the Asian Monsoon. The Chicago Water Isotope Spectrometer (ChiWIS) flew on high-altitude aircraft in the monsoon center during the StratoClim (2017) campaign out of Nepal, and in monsoon outflow during ACCLIP (2022) out of South Korea. Both campaigns sampled a broad range of convective and post-convective conditions, letting us trace how convective ice sublimates, reforms, and leaves behind characteristic isotopic signatures. We use the Bin Resolved Isotopic Microphysical Model (BRIMM), along with TRACZILLA backtrajectories and convective interactions derived from cloud-top products, to follow the evolving isotopic composition along flight paths in both campaigns. Results support the wide diversity of isotopic enhancement seen in both campaigns and show how temperature cycles downstream of convective events progressively modify environmental isotopic compositions