In-situ estimates of the role of radiative cooling for shallow convective organization

2021 ◽  
Author(s):  
Benjamin Fildier ◽  
Caroline Muller ◽  
Ludovic Touze-Peiffer ◽  
Anna Lea Albright
Keyword(s):  
Boundary Layer ◽  
Radiative Transfer ◽  
Radiative Cooling ◽  
Shallow Convection ◽  
Field Campaign ◽  
Radiative Processes ◽  
Horizontal Gradients ◽  
Convective Organization

<p>This study investigates the role of radiative processes in shaping the spatial distribution of shallow clouds, using in-situ measurements retrieved during the EUREC4A field campaign. Horizontal gradients in atmospheric radiative cooling above the boundary layer had been advanced as important drivers of shallow circulation and low-level winds, through their effect on surface pressure gradients. Modeling studies first recognized their importance in idealized simulations of deep convection in radiative-convective equilibrium, then found a weaker role for idealized cases of very shallow convection; but recent work using remote-sensing data argued for their importance in strengthening the circulation close to the margin between dry and moist regions, on synoptic scales, arguing for a possible significance for these radiative effects on observed cloud structures.</p><p>Here we investigate cases of intermediate scale, observed during the EUREC<sup>4</sup>A field campaign, where shallow convection extends vertically up to 4 km, and whose spatial organization can be described on mesoscales as “fish” or “flower” patterns. We perform careful radiative transfer calculations, using state-of-the-art spectroscopic data and over two thousand of dropsondes and radiosondes launched, to capture the fine details of radiative cooling profiles usually missed by satellite measurements. The large number of sondes allows us to sample radiative cooling information for the organization pattern of interest and analyze it in conjunction with the direct wind and humidity measurements. We also use geostationary estimates of precipitable water in clear-sky in order to cross-check the sonde data, and connect them to the organization pattern and to the position of the moist margin.</p><p>Our results target the following relationships previously identified in idealized simulations: (a) between horizontal gradients in moisture and in top-of-the-boundary-layer radiative cooling, (b) between these radiative cooling gradients and surface wind anomalies across the moist margin, and (c) between the strength of surface winds as a function of the distance from the moist margin. These results will allow us to test the importance of radiative transfer processes in a real case of shallow convective organization.</p>

scholarly journals A Moist Conceptual Model for the Boundary Layer Structure and Radiatively Driven Shallow Circulations in the Trades

2019 ◽  
Vol 76 (5) ◽  
pp. 1289-1306 ◽  
Author(s):  
Ann Kristin Naumann ◽  
Bjorn Stevens ◽  
Cathy Hohenegger
Keyword(s):  
Boundary Layer ◽  
Conceptual Model ◽  
Mass Flux ◽  
Large Scale ◽  
Layer Structure ◽  
Radiative Cooling ◽  
Shallow Convection ◽  
Tropical Oceans ◽  
Moderate Range ◽  
Convective Mass Flux

Abstract A conceptual model is developed to analyze how radiative cooling and the effect of moisture and shallow convection modify the boundary layer (BL) structure and the strength of mesoscale shallow circulations. The moist BL allows for a convective mass flux to modify the BL mass balance, which enhances inversion entrainment compared to a dry case and acts as a moisture valve to the BL. The convective mass flux is found to be insensitive to the applied radiative cooling and in the absence of heterogeneities cloud-free conditions exist only for unusual large-scale forcings. The model is able to explain the moderate range of BL heights and humidities observed in the trades. In a two-column setup, differential radiative BL cooling causes a pressure difference, which drives a BL flow from the cold and moist column to the warm and dry column and couples them dynamically. The small inversion buoyancy jump of the moist BL yields a stronger BL flow of 4 m s−1 instead of 1 m s−1 in the dry case. For typical conditions of the subsidence-dominated tropical oceans, a radiatively driven shallow circulation is stronger than one driven by sea surface temperature (SST) gradients. While the strength of the SST-driven circulation decreases with decreasing SST difference, the radiatively driven circulation is insensitive to the radiative BL cooling difference. In both cases, convection is suppressed in the descending branch of the shallow circulation and enhanced in the ascending branch, resembling patterns of organized shallow convection.

scholarly journals The Aerosols, Radiation and Clouds in Southern Africa Field Campaign in Namibia: Overview, Illustrative Observations, and Way Forward

2019 ◽  
Vol 100 (7) ◽  
pp. 1277-1298 ◽  
Author(s):  
Paola Formenti ◽  
Barbara D’Anna ◽  
Cyrille Flamant ◽  
Marc Mallet ◽  
Stuart John Piketh ◽  
...  
Keyword(s):  
Southern Africa ◽  
Marine Boundary Layer ◽  
Regional Climate ◽  
Mobile Station ◽  
Lower Troposphere ◽  
Anthropogenic Aerosols ◽  
Field Campaign ◽  
Radiative Processes ◽  
Surface Measurements

AbstractThe Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical properties of the lower troposphere. The focus laid on mineral dust emitted from salty pans and ephemeral riverbeds in northern Namibia, the advection of biomass-burning aerosol plumes from Angola subsequently transported over the Atlantic Ocean, and aerosols in the marine boundary layer at the ocean–atmosphere interface. This article presents an overview of the AEROCLO-sA field campaign with results from the airborne and surface measurements. These observations provide new knowledge of the interactions of aerosols and radiation in cloudy and clear skies in connection with the atmospheric dynamics over southern Africa. They will foster new advanced climate simulations and enhance the capability of spaceborne sensors, ultimately allowing a better prediction of future climate and weather in southern Africa.

scholarly journals Multidimensional Longwave Forcing of Boundary Layer Cloud Systems

2008 ◽  
Vol 65 (12) ◽  
pp. 3963-3977 ◽  
Author(s):  
David B. Mechem ◽  
Yefim L. Kogan ◽  
Mikhail Ovtchinnikov ◽  
Anthony B. Davis ◽  
K. Franklin Evans ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Radiative Transfer ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Dynamical Behavior ◽  
Radiative Cooling ◽  
Slight Reduction ◽  
Entrainment Rate ◽  
Cloud Systems ◽  
Eddy Simulation

Abstract The importance of multidimensional (MD) longwave radiative effects on cloud dynamics is evaluated in an eddy-resolving model (ERM)—the two-dimensional analog to large-eddy simulation (LES)—framework employing multidimensional radiative transfer [Spherical Harmonics Discrete Ordinate Method (SHDOM)]. Simulations are performed for a case of unbroken, marine boundary layer stratocumulus and a broken field of trade cumulus. “Snapshot” calculations of MD and independent pixel approximation (IPA; 1D) radiative transfer applied to simulated cloud fields show that the total radiative forcing changes only slightly, although the MD effects significantly modify the spatial structure of the radiative forcing. Simulations of each cloud type employing MD and IPA radiative transfer, however, differ little. For the solid cloud case, relative to using IPA, the MD simulation exhibits a slight reduction in entrainment rate and boundary layer total kinetic energy (TKE) relative to the IPA simulation. This reduction is consistent with both the slight decrease in net radiative forcing and a negative correlation between local vertical velocity and radiative forcing, which implies a damping of boundary layer eddies. Snapshot calculations of the broken cloud case suggest a slight increase in radiative cooling, although few systematic differences are noted in the interactive simulations. This result is attributed to the fact that radiative cooling is a relatively minor contribution to the total energetics. For the cloud systems in this study, the use of IPA longwave radiative transfer is sufficiently accurate to capture the dynamical behavior of boundary layer clouds. Further investigations are required to generalize this conclusion for other cloud types and longer time integrations.

scholarly journals Trade-wind clouds and aerosols characterized by airborne horizontal lidar measurements during the EUREC<sup>4</sup>A field campaign

2020 ◽  
Author(s):  
Patrick Chazette ◽  
Julien Totems ◽  
Alexandre Baron ◽  
Cyrille Flamant ◽  
Sandrine Bony
Keyword(s):  
Marine Boundary Layer ◽  
Horizontal Resolution ◽  
Trade Wind ◽  
Shallow Convection ◽  
Field Campaign ◽  
Lidar Measurements ◽  
Level 1 ◽  
Cloud Mask ◽  
Level 2

Abstract. From 23 January to 13 February 2020, twenty ATR-42 flights were conducted over the tropical Atlantic, off the coast of Barbados (−58°30' W 13°30' N), to characterize the trade-wind clouds generated by shallow convection. These flights were conducted as part of the international EUREC4A (Elucidating the role of clouds-circulation coupling in climate) field campaign. One of the objectives of these flights was to characterize the trade-wind cumuli at their base for a range of meteorological conditions, convective mesoscale organizations and times of the day, with the help of sidewards staring remote sensing (lidar and radar). This paper presents the datasets associated with horizontal lidar measurements. The lidar sampled clouds from a lateral window of the aircraft over a range of about 8 km, with a horizontal resolution of 15 to 30 m, over a rectangle pattern of 20 km by 130 km. The measurements made it possible to characterize the size distribution of clouds near their base, and the presence of dust-like aerosols within and above the marine boundary layer. This paper presents the measurements and the different levels of data processing, ranging from raw level 1 data (https://doi.org/10.25326/57; Chazette et al., 2020c) to level 2 and 3 processed data that include an horizontal cloud mask (https://doi.org/10.25326/58; Chazette et al., 2020b) and aerosol extinction coefficients (https://doi.org/10.25326/59; Chazette et al., 2020a). An intermediate level, companion to the level 1 data (level 1.5), is also available for calibrated and geolocalized data ( https://doi.org/10.25326/57; Chazette et al., 2020c).

Recommendations for In Situ and Remote Sensing Capabilities in Atmospheric Convection and Turbulence

2018 ◽  
Vol 99 (12) ◽  
pp. 2463-2470 ◽  
Author(s):  
Bart Geerts ◽  
David J. Raymond ◽  
Vanda Grubišić ◽  
Christopher A. Davis ◽  
Mary C. Barth ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
National Science Foundation ◽  
Shallow Convection ◽  
Boundary Layer Flows ◽  
Stable Boundary Layers ◽  
Remote Sensors ◽  
National Science ◽  
New Facilities

AbstractRecommendations are presented for in situ and remote sensing instruments and capabilities needed to advance the study of convection and turbulence in the atmosphere. These recommendations emerged from a community workshop held on 22–24 May 2017 at the National Center for Atmospheric Research and sponsored by the National Science Foundation. Four areas of research were distinguished at this workshop: i) boundary layer flows, including convective and stable boundary layers over heterogeneous land use and terrain conditions; ii) dynamics and thermodynamics of convection, including deep and shallow convection and continental and maritime convection; iii) turbulence above the boundary layer in clouds and in clear air, terrain driven and elsewhere; and iv) cloud microphysical and chemical processes in convection, including cloud electricity and lightning.The recommendations presented herein address a series of facilities and capabilities, ranging from existing ones that continue to fulfill science needs and thus should be retained and/or incrementally improved, to urgently needed new facilities, to desired capabilities for which no adequate solutions are as yet on the horizon. A common thread among all recommendations is the need for more highly resolved sampling, both in space and in time. Significant progress is anticipated, especially through the improved availability of airborne and ground-based remote sensors to the National Science Foundation (NSF)-supported community.

scholarly journals C<sup>3</sup>ONTEXT: A Common Consensus on Convective OrgaNizaTion during the EUREC<sup>4</sup>A eXperimenT

2021 ◽  
Author(s):  
Hauke Schulz
Keyword(s):  
Satellite Images ◽  
Shallow Convection ◽  
Field Campaign ◽  
Future Studies ◽  
Full Dataset ◽  
The Common ◽  
Cloud Patterns ◽  
Meso Scale ◽  
Good Agreement ◽  
Convective Organization

Abstract. The C3ONTEXT (A Common Consensus on Convective OrgaNizaTion during the EUREC4A eXperimenT) dataset is presented as an overview about the meso-scale cloud patterns identified during the EUREC4A field campaign in early 2020. Based on infrared and visible satellite images, 50 researchers of the EUREC4A science team manually identified the four prevailing meso-scale patterns of shallow convection observed by Stevens et al. (2020). The common consensus on the observed meso-scale cloud patterns emerging from these manual classifications is presented. It builds the basis for future studies and reduces the subjective nature of these visually defined cloud patterns. This consensus makes it possible to contextualize the measurements of the EUREC4A field campaign and interpret them in the meso-scale setting. Commonly used approaches to capture the meso-scale patterns are computed for comparison and show good agreement with the manual classifications. All four patterns as classified by Stevens et al. (2020) were present in January–February 2020 although not all were dominant during the observing period of EUREC4A. The full dataset including postprocessed datasets for easier usage are openly available at the Zenodo archive at https://doi. org/10.5281/zenodo.5724585 (Schulz, 2021b).

scholarly journals Trade-wind clouds and aerosols characterized by airborne horizontal lidar measurements during the EUREC<sup>4</sup>A field campaign

2020 ◽  
Vol 12 (4) ◽  
pp. 2919-2936
Author(s):  
Patrick Chazette ◽  
Julien Totems ◽  
Alexandre Baron ◽  
Cyrille Flamant ◽  
Sandrine Bony
Keyword(s):  
Marine Boundary Layer ◽  
Horizontal Resolution ◽  
Trade Wind ◽  
Shallow Convection ◽  
Field Campaign ◽  
Lidar Measurements ◽  
Level 3 ◽  
Level 1 ◽  
Cloud Mask

Abstract. From 23 January to 13 February 2020, 20 manned research flights were conducted over the tropical Atlantic, off the coast of Barbados (13∘30′ N, 58∘30′ W), to characterize the trade-wind clouds generated by shallow convection. These flights were conducted as part of the international EUREC4A (Elucidating the role of cloud–circulation coupling in climate) field campaign. One of the objectives of these flights was to characterize the trade-wind cumuli at their base for a range of meteorological conditions, convective mesoscale organizations and times of the day, with the help of sidewards-staring remote sensing instruments (lidar and radar). This paper presents the datasets associated with horizontal lidar measurements. The lidar sampled clouds from a lateral window of the aircraft over a range of about 8 km, with a horizontal resolution of 15 m, over a rectangle pattern of 20 km by 130 km. The measurements made possible the characterization of the size distribution of clouds near their base and the presence of dust-like aerosols within and above the marine boundary layer. This paper presents the measurements and the different levels of data processing, ranging from the raw Level 1 data (https://doi.org/10.25326/57; Chazette et al., 2020c) to the Level 2 and Level 3 processed data that include a horizontal cloud mask (https://doi.org/10.25326/58; Chazette et al., 2020b) and aerosol extinction coefficients (https://doi.org/10.25326/59; Chazette et al., 2020a). An intermediate level, companion to Level 1 data (Level 1.5), is also available for calibrated and geolocalized data (https://doi.org/10.25326/57; Chazette et al., 2020c).

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