scholarly journals EUREC<sup>4</sup>A observations from the SAFIRE ATR42 aircraft

2022 ◽  
Author(s):  
Sandrine Bony ◽  
Marie Lothon ◽  
Julien Delanoë ◽  
Pierre Coutris ◽  
Jean-Claude Etienne ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Flight Pattern ◽  
Cloud Radar ◽  
Base Level ◽  
Microphysical Properties ◽  
Research Aircraft

Abstract. As part of the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field campaign, which took place in January and February 2020 over the western tropical Atlantic near Barbados, the French SAFIRE ATR42 research aircraft conducted 19 flights in the lower troposphere. Each flight followed a common flight pattern that sampled the atmosphere around the cloud-base level, at different heights of the subcloud layer, near the sea surface and in the lower free troposphere. The aircraft's payload included a backscatter lidar and a Doppler cloud radar that were both horizontally oriented, a Doppler cloud radar looking upward, microphysical probes, a cavity ring-down spectrometer for water isotopes, a multiwavelength radiometer, a visible camera and multiple meteorological sensors, including fast rate sensors for turbulence measurements. With this instrumentation, the ATR characterized the macrophysical and microphysical properties of trade-wind clouds together with their thermodynamical, turbulent and radiative environment. This paper presents the airborne operations, the flight segmentation, the instrumentation, the data processing and the EUREC4A datasets produced from the ATR measurements. It shows that the ATR measurements of humidity, wind and cloud-base cloud fraction measured with different techniques and samplings are internally consistent, that meteorological measurements are consistent with estimates from dropsondes launched from an overflying aircraft (HALO), and that water isotopic measurements are well correlated with data from the Barbados Cloud Observatory. This consistency demonstrates the robustness of the ATR measurements of humidity, wind, cloud-base cloud fraction and water isotopic composition during EUREC4A. It also confirms that through their repeated flight patterns, the ATR and HALO measurements provided a statistically consistent sampling of trade-wind clouds and of their environment. The ATR datasets are freely available at the locations specified in Table 11.

scholarly journals On the imprint of the mesoscale organization of tradewind clouds at cloud base and below

2021 ◽  
Author(s):  
Sandrine Bony ◽  
Pierre-Etienne Brilouet ◽  
Patrick Chazette ◽  
Pierre Coutris ◽  
Julien Delanoë ◽  
...  
Keyword(s):  
Large Scale ◽  
Lower Troposphere ◽  
Cloud Base ◽  
Trade Wind ◽  
Tropical Atlantic ◽  
Lidar Measurements ◽  
Research Aircraft ◽  
Cloud Patterns

&lt;p&gt;&lt;span&gt;Trade-wind clouds &lt;/span&gt;&lt;span&gt;can &lt;/span&gt;&lt;span&gt;exhibit &lt;/span&gt;&lt;span&gt;different&lt;/span&gt;&lt;span&gt; patterns of mesoscale organization. These patterns were observed during the EUREC&lt;/span&gt;&lt;sup&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;A &lt;/span&gt;&lt;span&gt;(Elucidating the role of cloud-circulation coupling in climate) &lt;/span&gt;&lt;span&gt;field campaign that took place in Jan-Feb 2020 over the western tropical Atlantic near Barbados: &lt;/span&gt;&lt;span&gt;w&lt;/span&gt;&lt;span&gt;hile the HALO aircraft &lt;/span&gt;&lt;span&gt;was observing clouds from&lt;/span&gt; &lt;span&gt;above&lt;/span&gt;&lt;span&gt; and &lt;/span&gt;&lt;span&gt;was &lt;/span&gt;&lt;span&gt;characteri&lt;/span&gt;&lt;span&gt;z&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt; &lt;span&gt;the &lt;/span&gt;&lt;span&gt;large-scale&lt;/span&gt;&lt;span&gt; environment&lt;/span&gt; &lt;span&gt;with&lt;/span&gt;&lt;span&gt; dropsondes&lt;/span&gt;&lt;span&gt;, the ATR-42 research aircraft was flying &lt;/span&gt;&lt;span&gt;in&lt;/span&gt;&lt;span&gt; the &lt;/span&gt;&lt;span&gt;lower troposphere&lt;/span&gt;&lt;span&gt;,&lt;/span&gt; &lt;span&gt;characteriz&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt; cloud&lt;/span&gt;&lt;span&gt;s &lt;/span&gt;&lt;span&gt;and turbulence &lt;/span&gt;&lt;span&gt;with horizontal radar-lidar measurements and in-situ &lt;/span&gt;&lt;span&gt;probes and &lt;/span&gt;&lt;span&gt;sensors&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;By&lt;/span&gt;&lt;span&gt; analyz&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt; &lt;span&gt;these data &lt;/span&gt;&lt;span&gt;for different cloud patterns&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;we&lt;/span&gt; &lt;span&gt;investigate the &lt;/span&gt;&lt;span&gt;extent to which the &lt;/span&gt;&lt;span&gt;cloud&lt;/span&gt;&lt;span&gt; organization &lt;/span&gt;&lt;span&gt;i&lt;/span&gt;&lt;span&gt;s imprinted &lt;/span&gt;&lt;span&gt;in&lt;/span&gt;&lt;span&gt; cloud-base &lt;/span&gt;&lt;span&gt;properties &lt;/span&gt;&lt;span&gt;and&lt;/span&gt;&lt;span&gt; subcloud-layer &lt;/span&gt;&lt;span&gt;heterogeneities&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;The implications of our findings for understanding the roots of the mesoscale organization &lt;/span&gt;&lt;span&gt;of tradewind clouds&lt;/span&gt;&lt;span&gt; will be discussed.&lt;/span&gt;&lt;/p&gt;

scholarly journals Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

2014 ◽  
Vol 14 (13) ◽  
pp. 6695-6716 ◽  
Author(s):  
A. Muhlbauer ◽  
I. L. McCoy ◽  
R. Wood
Keyword(s):  
Physical Properties ◽  
Global Scale ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Radiative Effects ◽  
Regional Variability ◽  
Microphysical Properties ◽  
Low Clouds ◽  
Low Cloud

Abstract. An artificial neural network cloud classification scheme is combined with A-train observations to characterize the physical properties and radiative effects of marine low clouds based on their morphology and type of mesoscale cellular convection (MCC) on a global scale. The cloud morphological categories are (i) organized closed MCC, (ii) organized open MCC and (iii) cellular but disorganized MCC. Global distributions of the frequency of occurrence of MCC types show clear regional signatures. Organized closed and open MCCs are most frequently found in subtropical regions and in midlatitude storm tracks of both hemispheres. Cellular but disorganized MCC are the predominant type of marine low clouds in regions with warmer sea surface temperature such as in the tropics and trade wind zones. All MCC types exhibit a pronounced seasonal cycle. The physical properties of MCCs such as cloud fraction, radar reflectivity, drizzle rates and cloud top heights as well as the radiative effects of MCCs are found highly variable and a function of the type of MCC. On a global scale, the cloud fraction is largest for closed MCC with mean cloud fractions of about 90%, whereas cloud fractions of open and cellular but disorganized MCC are only about 51% and 40%, respectively. Probability density functions (PDFs) of cloud fractions are heavily skewed and exhibit modest regional variability. PDFs of column maximum radar reflectivities and inferred cloud base drizzle rates indicate fundamental differences in the cloud and precipitation characteristics of different MCC types. Similarly, the radiative effects of MCCs differ substantially from each other in terms of shortwave reflectance and transmissivity. These differences highlight the importance of low-cloud morphologies and their associated cloudiness on the shortwave cloud forcing.

scholarly journals Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

2014 ◽  
Vol 14 (5) ◽  
pp. 6981-7023 ◽  
Author(s):  
A. Muhlbauer ◽  
I. L. McCoy ◽  
R. Wood
Keyword(s):  
Physical Properties ◽  
Global Scale ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Radiative Effects ◽  
Regional Variability ◽  
Microphysical Properties ◽  
Low Clouds ◽  
Low Cloud

Abstract. An artificial neural network cloud classification scheme is combined with A-Train observations to characterize the physical properties and radiative effects of marine low clouds based on their morphology and type of mesoscale cellular convection (MCC) on a global scale. The cloud morphological categories are (i) organized closed MCC, (ii) organized open MCC and (iii) cellular but disorganized MCC. Global distributions of the frequency of occurrence of MCC types show clear regional signatures. Organized closed and open MCCs are most frequently found in subtropical regions and in mid-latitude storm tracks of both hemispheres. Cellular but disorganized MCC are the predominant type of marine low clouds in regions with warmer sea surface temperature such as in the tropics and trade wind zones. All MCC types exhibit a pronounced seasonal cycle. The physical properties of MCCs such as cloud fraction, radar reflectivity, drizzle rates and cloud top heights as well as the radiative effects of MCCs are found highly variable and a function of the type of MCC. On a global scale, the cloud fraction is largest for closed MCC with mean cloud fractions of about 90% whereas cloud fractions of open and cellular but disorganized MCC are only about 51% and 40%, respectively. Probability density functions (PDFs) of cloud fractions are heavily skewed and exhibit modest regional variability. PDFs of column maximum radar reflectivities and inferred cloud base drizzle rates indicate fundamental differences in the cloud and precipitation characteristics of different MCC types. Similarly, the radiative effects of MCCs differ substantially from each other in terms of shortwave reflectance and transmissivity. These differences highlight the importance of low cloud morphologies and their associated cloudiness on the shortwave cloud forcing.

scholarly journals Improvement of airborne retrievals of cloud droplet number concentration of trade wind cumulus using a synergetic approach

2019 ◽  
Vol 12 (3) ◽  
pp. 1635-1658 ◽  
Author(s):  
Kevin Wolf ◽  
André Ehrlich ◽  
Marek Jacob ◽  
Susanne Crewell ◽  
Martin Wirth ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Cloud Base ◽  
Trade Wind ◽  
Liquid Water Path ◽  
Cloud Properties ◽  
Research Aircraft ◽  
Cloud Droplet Number Concentration

Abstract. In situ measurements of cloud droplet number concentration N are limited by the sampled cloud volume. Satellite retrievals of N suffer from inherent uncertainties, spatial averaging, and retrieval problems arising from the commonly assumed strictly adiabatic vertical profiles of cloud properties. To improve retrievals of N it is suggested in this paper to use a synergetic combination of passive and active airborne remote sensing measurement, to reduce the uncertainty of N retrievals, and to bridge the gap between in situ cloud sampling and global averaging. For this purpose, spectral solar radiation measurements above shallow trade wind cumulus were combined with passive microwave and active radar and lidar observations carried out during the second Next Generation Remote Sensing for Validation Studies (NARVAL-II) campaign with the High Altitude and Long Range Research Aircraft (HALO) in August 2016. The common technique to retrieve N is refined by including combined measurements and retrievals of cloud optical thickness τ, liquid water path (LWP), cloud droplet effective radius reff, and cloud base and top altitude. Three approaches are tested and applied to synthetic measurements and two cloud scenarios observed during NARVAL-II. Using the new combined retrieval technique, errors in N due to the adiabatic assumption have been reduced significantly.

Measuring the variability of the shallow convective mass flux profiles in the tropical trade wind region

2020 ◽  
Author(s):  
Marcus Klingebiel ◽  
Heike Konow ◽  
Bjorn Stevens
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Doppler Radar ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Geophysical Research ◽  
Wind Region ◽  
Convective Mass Flux

&lt;p&gt;Mass flux is a key parameter to represent shallow convection in global circulation models. To estimate the shallow convective mass flux as accurately as possible, observations of this parameter are necessary. Prior studies from Ghate et al. (2011) and Lamer et al. (2015) used Doppler radar measurements over a few months to identify a typical shallow convective mass flux profile based on cloud fraction and vertical velocity. In this study, we extend their observations by using long term remote sensing measurements at the Barbados Cloud Observatory (13&amp;#176; 09&amp;#8217; N, 59&amp;#176; 25&amp;#8217; W) over a time period of 30 months and check a hypothesis by Grant (2001), who proposed that the cloud base mass flux is just proportional to the sub-cloud convective velocity scale. Therefore, we analyze Doppler radar and Doppler lidar measurements to identify the variation of the vertical velocity in the cloud and sub-cloud layer, respectively. Furthermore, we show that the in-cloud mass flux is mainly influenced by the cloud fraction and provide a linear equation, which can be used to roughly calculate the mass flux in the trade wind region based on the cloud fraction.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;br&gt;Ghate,&amp;#160; V.&amp;#160; P.,&amp;#160; M.&amp;#160; A.&amp;#160; Miller,&amp;#160; and&amp;#160; L.&amp;#160; DiPretore,&amp;#160; 2011:&amp;#160;&amp;#160; Vertical&amp;#160; velocity structure of marine boundary layer trade wind cumulus clouds. Journal&amp;#160; of&amp;#160; Geophysical&amp;#160; Research: Atmospheres, 116&amp;#160; (D16), doi:10.1029/2010JD015344.&lt;/p&gt;&lt;p&gt;Grant,&amp;#160; A.&amp;#160; L.&amp;#160; M.,&amp;#160; 2001:&amp;#160;&amp;#160; Cloud-base&amp;#160; fluxes&amp;#160; in&amp;#160; the&amp;#160; cumulus-capped boundary layer. Quarterly Journal of the Royal Meteorological Society, 127 (572), 407&amp;#8211;421, doi:10.1002/qj.49712757209.&lt;/p&gt;&lt;p&gt;Lamer, K., P. Kollias, and L. Nuijens, 2015:&amp;#160; Observations of the variability&amp;#160; of&amp;#160; shallow&amp;#160; trade&amp;#160; wind&amp;#160; cumulus&amp;#160; cloudiness&amp;#160; and&amp;#160; mass&amp;#160; flux. Journal of Geophysical Research: Atmospheres, 120&amp;#160; (12), 6161&amp;#8211;6178, doi:10.1002/2014JD022950.&lt;/p&gt;

A 19-Month Record of Marine Aerosol–Cloud–Radiation Properties Derived from DOE ARM Mobile Facility Deployment at the Azores. Part I: Cloud Fraction and Single-Layered MBL Cloud Properties

2014 ◽  
Vol 27 (10) ◽  
pp. 3665-3682 ◽  
Author(s):  
Xiquan Dong ◽  
Baike Xi ◽  
Aaron Kennedy ◽  
Patrick Minnis ◽  
Robert Wood
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Liquid Water ◽  
Mixed Boundary ◽  
Cloud Condensation Nuclei ◽  
Low Pressure ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Microphysical Properties ◽  
Cloud Properties

Abstract A 19-month record of total and single-layered low (&lt;3 km), middle (3–6 km), and high (&gt;6 km) cloud fractions (CFs) and the single-layered marine boundary layer (MBL) cloud macrophysical and microphysical properties was generated from ground-based measurements at the Atmospheric Radiation Measurement Program (ARM) Azores site between June 2009 and December 2010. This is the most comprehensive dataset of marine cloud fraction and MBL cloud properties. The annual means of total CF and single-layered low, middle, and high CFs derived from ARM radar and lidar observations are 0.702, 0.271, 0.01, and 0.106, respectively. Greater total and single-layered high (&gt;6 km) CFs occurred during the winter, whereas single-layered low (&lt;3 km) CFs were more prominent during summer. Diurnal cycles for both total and low CFs were stronger during summer than during winter. The CFs are bimodally distributed in the vertical with a lower peak at ~1 km and a higher peak between 8 and 11 km during all seasons, except summer when only the low peak occurs. Persistent high pressure and dry conditions produce more single-layered MBL clouds and fewer total clouds during summer, whereas the low pressure and moist air masses during winter generate more total and multilayered clouds, and deep frontal clouds associated with midlatitude cyclones. The seasonal variations of cloud heights and thickness are also associated with the seasonal synoptic patterns. The MBL cloud layer is low, warm, and thin with large liquid water path (LWP) and liquid water content (LWC) during summer, whereas during winter it is higher, colder, and thicker with reduced LWP and LWC. The cloud LWP and LWC values are greater at night than during daytime. The monthly mean daytime cloud droplet effective radius re values are nearly constant, while the daytime droplet number concentration Nd basically follows the LWC variation. There is a strong correlation between cloud condensation nuclei (CCN) concentration NCCN and Nd during January–May, probably due to the frequent low pressure systems because upward motion brings more surface CCN to cloud base (well-mixed boundary layer). During summer and autumn, the correlation between Nd and NCCN is not as strong as that during January–May because downward motion from high pressure systems is predominant. Compared to the compiled aircraft in situ measurements during the Atlantic Stratocumulus Transition Experiment (ASTEX), the cloud microphysical retrievals in this study agree well with historical aircraft data. Different air mass sources over the ARM Azores site have significant impacts on the cloud microphysical properties and surface CCN as demonstrated by great variability in NCCN and cloud microphysical properties during some months.

scholarly journals Meteorological and Aerosol Effects on Marine Stratocumulus

2016 ◽  
Vol 73 (2) ◽  
pp. 807-820 ◽  
Author(s):  
Zhe Li ◽  
Huiwen Xue ◽  
Jen-Ping Chen ◽  
Wei-Chyung Wang
Keyword(s):  
Precipitation Amount ◽  
Wrf Model ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Diurnal Cycles ◽  
Microphysical Properties ◽  
Southeastern Pacific ◽  
Lower Cloud

Abstract This study investigates the effects of meteorological conditions and aerosols on marine stratocumulus in the southeastern Pacific using the Weather Research and Forecasting (WRF) Model. Two regimes with different temperature and moisture conditions in the finest model domain are investigated. The western regime is around 87°–79°W, while the eastern regime is around 79°–71°W. In both regimes, cloud fraction, liquid water path (LWP), cloud thickness, and precipitation show significant diurnal cycles. Cloud fraction can be 0.83 during the night and down to 0.29 during the day in the western regime. The diurnal cycles in the eastern regime have smaller amplitudes but are still very strong. Stratocumulus properties also differ in the two regimes. Compared to the western regime, the eastern regime has lower temperature, higher relative humidity, and a more coupled boundary layer, leading to higher cloud fraction (by 0.11) and lower cloud-base height. The eastern regime also has lower inversion height that causes lower cloud-top height and thinner clouds and, hence, lower LWP and less precipitation. Cloud microphysical properties are very sensitive to aerosols in both regimes. Increasing aerosols greatly increase cloud number concentration, decrease cloud effective radius, and suppress precipitation. Cloud macrophysical properties (cloud fraction, LWP) are not sensitive to aerosols in either regime, most notably in the eastern regime where precipitation amount is less. The changes in cloud fraction and LWP caused by changes in aerosol concentrations are smaller than the changes in the diurnal cycle and the spatial variability between the two regimes.

scholarly journals Shallow cumulus cloud feedback in large eddy simulations – bridging the gap to storm-resolving models

2021 ◽  
Vol 21 (5) ◽  
pp. 3275-3288
Author(s):  
Jule Radtke ◽  
Thorsten Mauritsen ◽  
Cathy Hohenegger
Keyword(s):  
Cloud Cover ◽  
Horizontal Resolution ◽  
Cloud Fraction ◽  
Cloud Feedback ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Carry Over

Abstract. The response of shallow trade cumulus clouds to global warming is a leading source of uncertainty in projections of the Earth's changing climate. A setup based on the Rain In Cumulus over the Ocean field campaign is used to simulate a shallow trade wind cumulus field with the Icosahedral Nonhydrostatic Large Eddy Model in a control and a perturbed 4 K warmer climate, while degrading horizontal resolution from 100 m to 5 km. As the resolution is coarsened, the base-state cloud fraction increases substantially, especially near cloud base, lateral mixing is weaker, and cloud tops reach higher. Nevertheless, the overall vertical structure of the cloud layer is surprisingly robust across resolutions. In a warmer climate, cloud cover reduces, alone constituting a positive shortwave cloud feedback: the strength correlates with the amount of base-state cloud fraction and thus is stronger at coarser resolutions. Cloud thickening, resulting from more water vapour availability for condensation in a warmer climate, acts as a compensating feedback, but unlike the cloud cover reduction it is largely resolution independent. Therefore, refining the resolution leads to convergence to a near-zero shallow cumulus feedback. This dependence holds in experiments with enhanced realism including precipitation processes or warming along a moist adiabat instead of uniform warming. Insofar as these findings carry over to other models, they suggest that storm-resolving models may exaggerate the trade wind cumulus cloud feedback.

scholarly journals The vertical structure and spatial variability of lower-tropospheric water vapor and clouds in the trades

2020 ◽  
Vol 20 (10) ◽  
pp. 6129-6145
Author(s):  
Ann Kristin Naumann ◽  
Christoph Kiemle
Keyword(s):  
Water Vapor ◽  
Cloud Fraction ◽  
Airborne Lidar ◽  
Cloud Base ◽  
Trade Wind ◽  
Model Resolution ◽  
Grid Spacing ◽  
Model Bias ◽  
Shallow Cumulus ◽  
Vapor Distribution

Abstract. Horizontal and vertical variability of water vapor is omnipresent in the tropics, but its interaction with cloudiness poses challenges for weather and climate models. In this study we compare airborne lidar measurements from a summer and a winter field campaign in the tropical Atlantic with high-resolution simulations to analyze the water vapor distributions in the trade wind regime, its covariation with cloudiness, and their representation in simulations. Across model grid spacing from 300 m to 2.5 km, the simulations show good skill in reproducing the water vapor distribution in the trades as measured by the lidar. An exception to this is a pronounced moist model bias at the top of the shallow cumulus layer in the dry winter season which is accompanied by a humidity gradient that is too weak at the inversion near the cloud top. The model's underestimation of water vapor variability in the cloud and subcloud layer occurs in both seasons but is less pronounced than the moist model bias at the inversion. Despite the model's insensitivity to resolution from hecto- to kilometer scale for the distribution of water vapor, cloud fraction decreases strongly with increasing model resolution and is not converged at hectometer grid spacing. The observed cloud deepening with increasing water vapor path is captured well across model resolution, but the concurrent transition from cloud-free to low cloud fraction is better represented at hectometer resolution. In particular, in the wet summer season the simulations with kilometer-scale resolution overestimate the observed cloud fraction near the inversion but lack condensate near the observed cloud base. This illustrates how a model's ability to properly capture the water vapor distribution does not necessarily translate into an adequate representation of shallow cumulus clouds that live at the tail of the water vapor distribution.

scholarly journals Remote Sensing of Sea Salt Aerosol below Trade Wind Clouds

2019 ◽  
Vol 76 (5) ◽  
pp. 1189-1202 ◽  
Author(s):  
Marcus Klingebiel ◽  
Virendra P. Ghate ◽  
Ann Kristin Naumann ◽  
Florian Ditas ◽  
Mira L. Pöhlker ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Relative Humidity ◽  
Sea Salt ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Clouds ◽  
Ka Band ◽  
Sea Salt Aerosol ◽  
Cloud Radar ◽  
Shallow Cumulus

Abstract Sea salt aerosol in the boundary layer below shallow cumulus clouds is remotely observed with a Ka-band cloud radar at the Barbados Cloud Observatory and is detected in 76% of the measurements over 1 year. Carried by convection, sea salt particles with a diameter larger than 500 nm show an upward motion of 0.2 m s−1 below shallow cumulus clouds for a 2-day case study. Caused by an increasing relative humidity with increasing altitude, the sea salt particles become larger as they move closer to the cloud base. By using combined measurements of a Ka-band cloud radar and a Raman lidar, the retrieved equivolumetric diameter of the hygroscopically grown sea salt particles is found to be between 6 and 11 μm with a total number concentration of 20 cm−3 near cloud base. Assuming a fixed shape parameter, a size distribution of sea salt particles under high-relative-humidity conditions below cloud base is estimated and agrees with measurements taken by a dry-deposition sampler and online aerosol observations. The methods outlined in this paper can be used in future studies to get a better understanding of the vertical and temporal sea salt distribution in the boundary layer and sea salt aerosol–cloud interaction processes.

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