The contribution of convection to the stratospheric water vapor: the first budget using a Global-Storm-Resolving Model

The deepest convection on Earth injects water in the tropical stratosphere, but its contribution to the global stratospheric water budget remains uncertain. The Global Storm-Resolving Model ICOsahedral Non-hydrostatic is used to simulate the moistening of the lower stratosphere for 40 days during boreal summer. The decomposition of the water vapor budget in the tropical lower stratosphere (TLS, 10°S–30°N, and 17–20 km altitude) indicates that the average moistening (+21 Tg) over the simulated 40-day period is the result of the combined effect of the vertical water vapor transport from the troposphere (+27 Tg), microphysical phase changes and subgrid-scale transport (+2 Tg), partly compensated by horizontal water vapor export (−8 Tg). The very deep convective systems, explicitly represented thanks to the employed 2.5 km grid spacing of the model, are identified using the very low Outgoing Longwave Radiation of their cold cloud tops. The water vapor budget reveals that the vertical transport, the sublimation and the subgrid-scale transport at their top contribute together to 11% of the water vapor mass input into the TLS

The mechanisms leading to a stratospheric hydration by overshooting convection

AbstractOvershoots are convective air parcels that rise beyond their level of neutral buoyancy. A giga-large-eddy simulation (100-m cubic resolution) of “Hector the Convector,” a deep convective system that regularly forms in northern Australia, is analyzed to identify overshoots and quantify the effect of hydration of the stratosphere. In the simulation, 1507 individual overshoots were identified, and 46 of them were tracked over more than 10 min. Hydration of the stratosphere occurs through a sequence of mechanisms: overshoot penetration into the stratosphere, followed by entrainment of stratospheric air and then by efficient turbulent mixing between the air in the overshoot and the entrained warmer air, leaving the subsequent mixed air at about the maximum overshooting altitude. The time scale of these mechanisms is about 1 min. Two categories of overshoots are distinguished: those that significantly hydrate the stratosphere and those that have little direct hydration effect. The former reach higher altitudes and hence entrain and mix with air that has higher potential temperatures. The resulting mixed air has higher temperatures and higher saturation mixing ratios. Therefore, a greater amount of the hydrometeors carried by the original overshoot sublimates to form a persistent vapor-enriched layer. This makes the maximum overshooting altitude the key prognostic for the parameterization of deep convection to represent the correct overshoot transport. One common convection parameterization is tested, and the results suggest that the overshoot downward acceleration due to negative buoyancy is too large relative to that predicted by the numerical simulations and needs to be reduced.This research was supported by the StratoClim project funded by the European Union Seventh Framework Programme under Grant Agree- ment 603557 and the Idex Teasao project. Todd Lane is supported by the Australian Research Council’s Centres of Excellence scheme (CE170100023). Computer re- sources were allocated by GENCI through Projects 90569 and 100231 (Grand Challenge Turing)

Ice injected into the tropopause by deep convection - Part 2: Over the Maritime Continent

Abstract. The amount of ice injected into the tropical tropopause layer has a strong radiative impact on climate. A companion paper (Part 1) used the amplitude of the diurnal cycle of ice water content (IWC) as an estimate of ice injection by deep convection, showed that the Maritime Continent (MariCont) region provides the largest injection to the upper troposphere (UT; 146 hPa) and to the tropopause level (TL; 100 hPa). This study focuses on the MariCont region and extends that approach to assess the processes, the areas and the diurnal amount and duration of ice injected over islands and over seas during the austral convective season. The model presented in the companion paper is again used to estimate the amount of ice injected (ΔIWC) by combining ice water content (IWC) measured twice a day by the Microwave Limb Sounder (MLS; Version 4.2) from 2004 to 2017 and precipitation (Prec) measurements from the Tropical Rainfall Measurement Mission (TRMM; Version 007) binned at high temporal resolution (1 h). The horizontal distribution of ΔIWC estimated from Prec (ΔIWCPrec) is presented at 2∘×2∘ horizontal resolution over the MariCont. ΔIWC is also evaluated by using the number of lightning events (Flash) from the TRMM-LIS instrument (Lightning Imaging Sensor, from 2004 to 2015 at 1 h and 0.25∘ × 0.25∘ resolution). ΔIWCPrec and ΔIWC estimated from Flash (ΔIWCFlash) are compared to ΔIWC estimated from the ERA5 reanalyses (ΔIWCERA5) with the vertical resolution degraded to that of MLS observations (ΔIWCERA5). Our study shows that the diurnal cycles of Prec and Flash are consistent with each other in phase over land but different over offshore and coastal areas of the MariCont. The observational ΔIWC range between ΔIWCPrec and ΔIWCFlash, interpreted as the uncertainty of our model in estimating the amount of ice injected, is smaller over land (where ΔIWCPrec and ΔIWCFlash agree to within 22 %) than over ocean (where differences are up to 71 %) in the UT and TL. The impact of the MLS vertical resolution on the estimation of ΔIWC is greater in the TL (difference between ΔIWCERA5 and 〈ΔIWCERA5〉 of 32 % to 139 %, depending on the study zone) than in the UT (difference of 9 % to 33 %). Considering all the methods, in the UT, estimates of ΔIWC span 4.2 to 10.0 mg m−3 over land and 0.4 to 4.4 mg m−3 over sea, and in the TL estimates of ΔIWC span 0.5 to 3.9 mg m−3 over land and 0.1 to 0.7 mg m−3 over sea. Finally, based on IWC from MLS and ERA5, Prec and Flash, this study highlights that (1) at both levels, ΔIWC estimated over land can be more than twice that estimated over sea and (2) small islands with high topography present the largest ΔIWC (e.g., island of Java).This research has been supported by the Cen- tre National de la Recherche Scientifique-Institut National des Sci- ences de l’Univers (CNRS-INSU), Météo-France, and the Excel- lence Initiative (Idex) of Toulouse, France (grant no. 139225)

Ice injected into the tropopause by deep convection-Part 1: In the austral convective tropics

© Author(s) 2019. The contribution of deep convection to the amount of water vapour and ice in the tropical tropopause layer (TTL) from the tropical upper troposphere (UT; around 146 hPa) to the tropopause level (TL; around 100 hPa) is investigated. Ice water content (IWC) and water vapour (WV) measured in the UT and the TL by the Microwave Limb Sounder (MLS; Version 4.2) are compared to the precipitation (Prec) measured by the Tropical Rainfall Measurement Mission (TRMM; Version 007). The two datasets, gridded within 2° ×2° horizontal bins, have been analysed during the austral convective season, December, January, and February (DJF), from 2004 to 2017. MLS observations are performed at 01:30 and 13:30 local solar time, whilst the Prec dataset is constructed with a time resolution of 1 h. The new contribution of this study is to provide a much more detailed picture of the diurnal variation of ice than is provided by the very limited (two per day) MLS observations. Firstly, we show that IWC represents 70% and 50% of the total water in the tropical UT and TL, respectively, and that Prec is spatially highly correlated with IWC in the UT (Pearson's linear coefficient R=0:7). We propose a method that uses Prec as a proxy for deep convection bringing ice up to the UT and TL during the growing stage of convection, in order to estimate the amount of ice injected into the UT and the TL, respectively. We validate the method using ice measurements from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) during the period DJF 2009-2010. Next, the diurnal cycle of injection of IWC into the UT and the TL by deep convection is calculated by the difference between the maximum and the minimum in the estimated diurnal cycle of IWC in these layers and over selected convective zones. Six tropical highly convective zones have been chosen: South America, South Africa, Pacific Ocean, Indian Ocean, and the Maritime Continent region, split into land (MariCont-L) and ocean (MariCont-O). IWC injection is found to be 2.73 and 0.41 mgm -3 over tropical land in the UT and TL, respectively, and 0.60 and 0.13 mgm -3 over tropical ocean in the UT and TL, respectively. The MariCont-L region has the greatest ice injection in both the UT and TL (3.34 and 0.42-0.56 mgm -3 , respectively). The MariCont-O region has less ice injection than MariCont-L (0.91 mgm -3 in the UT and 0.16-0.34 mgm -3 in TL) but has the highest diurnal minimum value of IWC in the TL (0.34-0.37 mgm -3 ) among all oceanic zones

EUREC⁴A

The science guiding the EUREC⁴A campaign and its measurements is presented. EUREC⁴A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC⁴A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC⁴A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC⁴A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement

EUREC⁴A

The science guiding the EUREC⁴A campaign and its measurements is presented. EUREC⁴A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC⁴A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC⁴A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC⁴A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement

The Mechanisms Leading to a Stratospheric Hydration by Overshooting Convection

Overshoots are convective air parcels that rise beyond their level of neutral buoyancy. A giga-large-eddy simulation (100-m cubic resolution) of ''Hector the Convector,'' a deep convective system that regularly forms in northern Australia, is analyzed to identify overshoots and quantify the effect of hydration of the stratosphere. In the simulation, 1507 individual overshoots were identified, and 46 of them were tracked over more than 10 min. Hydration of the stratosphere occurs through a sequence of mechanisms: overshoot penetration into the stratosphere, followed by entrainment of stratospheric air and then by efficient turbulent mixing between the air in the overshoot and the entrained warmer air, leaving the subsequent mixed air at about the maximumovershooting altitude. The time scale of these mechanisms is about 1 min. Two categories of overshoots are distinguished: those that significantly hydrate the stratosphere and those that have little direct hydration effect. The former reach higher altitudes and hence entrain and mix with air that has higher potential temperatures. The resulting mixed air has higher temperatures and higher saturation mixing ratios. Therefore, a greater amount of the hydrometeors carried by the original overshoot sublimates to form a persistent vapor-enriched layer. This makes the maximum overshooting altitude the key prognostic for the parameterization of deep convection to represent the correct overshoot transport. One common convection parameterization is tested, and the results suggest that the overshoot downward acceleration due to negative buoyancy is too large relative to that predicted by the numerical simulations and needs to be reduced

Ice injected into the tropopause by deep convection-Part 1: In the austral convective tropics

© Author(s) 2019. The contribution of deep convection to the amount of water vapour and ice in the tropical tropopause layer (TTL) from the tropical upper troposphere (UT; around 146 hPa) to the tropopause level (TL; around 100 hPa) is investigated. Ice water content (IWC) and water vapour (WV) measured in the UT and the TL by the Microwave Limb Sounder (MLS; Version 4.2) are compared to the precipitation (Prec) measured by the Tropical Rainfall Measurement Mission (TRMM; Version 007). The two datasets, gridded within 2° ×2° horizontal bins, have been analysed during the austral convective season, December, January, and February (DJF), from 2004 to 2017. MLS observations are performed at 01:30 and 13:30 local solar time, whilst the Prec dataset is constructed with a time resolution of 1 h. The new contribution of this study is to provide a much more detailed picture of the diurnal variation of ice than is provided by the very limited (two per day) MLS observations. Firstly, we show that IWC represents 70% and 50% of the total water in the tropical UT and TL, respectively, and that Prec is spatially highly correlated with IWC in the UT (Pearson's linear coefficient R=0:7). We propose a method that uses Prec as a proxy for deep convection bringing ice up to the UT and TL during the growing stage of convection, in order to estimate the amount of ice injected into the UT and the TL, respectively. We validate the method using ice measurements from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) during the period DJF 2009-2010. Next, the diurnal cycle of injection of IWC into the UT and the TL by deep convection is calculated by the difference between the maximum and the minimum in the estimated diurnal cycle of IWC in these layers and over selected convective zones. Six tropical highly convective zones have been chosen: South America, South Africa, Pacific Ocean, Indian Ocean, and the Maritime Continent region, split into land (MariCont-L) and ocean (MariCont-O). IWC injection is found to be 2.73 and 0.41 mgm -3 over tropical land in the UT and TL, respectively, and 0.60 and 0.13 mgm -3 over tropical ocean in the UT and TL, respectively. The MariCont-L region has the greatest ice injection in both the UT and TL (3.34 and 0.42-0.56 mgm -3 , respectively). The MariCont-O region has less ice injection than MariCont-L (0.91 mgm -3 in the UT and 0.16-0.34 mgm -3 in TL) but has the highest diurnal minimum value of IWC in the TL (0.34-0.37 mgm -3 ) among all oceanic zones

Fennec dust forecast intercomparison over the Sahara in June 2011

In the framework of the Fennec international programme, a field campaign was conducted in June 2011 over the western Sahara. It led to the first observational data set ever obtained that documents the dynamics, thermodynamics and composition of the Saharan atmospheric boundary layer (SABL) under the influence of the heat low. In support to the aircraft operation, four dust forecasts were run daily at low and high resolutions with convection-parameterizing and convection-permitting models, respectively. The unique airborne and ground-based data sets allowed the first ever intercomparison of dust forecasts over the western Sahara. At monthly scale, large aerosol optical depths (AODs) were forecast over the Sahara, a feature observed by satellite retrievals but with different magnitudes. The AOD intensity was correctly predicted by the high-resolution models, while it was underestimated by the low-resolution models. This was partly because of the generation of strong near-surface wind associated with thunderstorm-related density currents that could only be reproduced by models representing convection explicitly. Such models yield emissions mainly in the afternoon that dominate the total emission over the western fringes of the Adrar des Iforas and the Aïr Mountains in the high-resolution forecasts. Over the western Sahara, where the harmattan contributes up to 80 % of dust emission, all the models were successful in forecasting the deep well-mixed SABL. Some of them, however, missed the large near-surface dust concentration generated by density currents and low-level winds. This feature, observed repeatedly by the airborne lidar, was partly forecast by one high-resolution model only

Ship- and island-based atmospheric soundings from the 2020 EUREC(4)A field campaign [Data paper]

To advance the understanding of the interplay among clouds, convection, and circulation, and its role in climate change, the Elucidating the role of clouds-circulation coupling in climate campaign (EUREC(4)A) and Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) collected measurements in the western tropical Atlantic during January and February 2020. Upper-air radiosondes were launched regularly (usually 4-hourly) from a network consisting of the Barbados Cloud Observatory (BCO) and four ships within 6-16 degrees N, 51-60 degrees W. From 8 January to 19 February, a total of 811 radiosondes measured wind, temperature, and relative humidity. In addition to the ascent, the descent was recorded for 82% of the soundings. The soundings sampled changes in atmospheric pressure, winds, lifting condensation level, boundary layer depth, and vertical distribution of moisture associated with different ocean surface conditions, synoptic variability, and mesoscale convective organization. Raw (Level 0), quality-controlled 1 s (Level 1), and vertically gridded (Level 2) data in NetCDF format (Stephan et al., 2020) are available to the public at AERIS (https://doi.org/10.25326/137). The methods of data collection and post-processing for the radiosonde data set are described here