Measurements from the University of Colorado RAAVEN Uncrewed Aircraft System during ATOMIC

Between 24 January and 15 February 2020, small uncrewed aircraft systems (sUASs) were deployed to Morgan Lewis (Barbados) as part of the Atlantic Tradewind Ocean–Atmosphere Mesoscale Interaction Campaign (ATOMIC), a sister project to the ElUcidating the RolE of Cloud-Circulation Coupling in ClimAte (EUREC4A) project. The observations from ATOMIC and EUREC4A were aimed at improving our understanding of trade-wind cumulus clouds and the environmental regimes supporting them and involved the deployment of a wide variety of observational assets, including aircraft, ships, surface-based systems, and profilers. The current paper describes ATOMIC observations obtained using the University of Colorado Boulder RAAVEN (Robust Autonomous Aerial Vehicle – Endurant Nimble) sUAS. This platform collected nearly 80 h of data throughout the lowest kilometer of the atmosphere, sampling the near-shore environment upwind from Barbados. Data from these platforms are publicly available through the National Oceanic and Atmospheric Administration's National Center for Environmental Intelligence (NCEI) archive. The primary DOI for the quality-controlled dataset described in this paper is https://doi.org/10.25921/jhnd-8e58 (de Boer et al., 2021).

Vertical Distributions of Aerosol and Cloud Microphysical Properties and the Aerosol Impact on a Continental Cumulus Cloud Based on Aircraft Measurements From the Loess Plateau of China

Based on aircraft measurements of aerosols and continental cumulus clouds made over the Loess Plateau of China (Xinzhou, Shanxi Province) on 30 July 2020, this study focuses on the vertical profiles of microphysical properties of aerosols and cumulus clouds, and use them to study aerosol-cloud interactions. During the study period, the boundary layer was stable with a height ∼1,500 m above sea level. Aerosols in the boundary layer mainly came from local emissions, while aerosols above this layer were mostly dust aerosols transported over long distances. Vertical profiles of aerosols and cloud condensation nuclei were obtained, and aerosol activation ratios at different supersaturation (SS) levels ranged from 0.16 to 0.32 at 0.2% SS and 0.70 to 0.85 at 0.8% SS. A thick cumulus cloud in the development stage was observed from the bottom to the top with the horizontal dimension of 10 km by 7 km, the cloud-base height of 2,450 m (15.8°C), and the cloud-top height of 5,400 m (−3°C). The maximum updraft velocity near the cloud top was 13.45 m s−1, and the maximum downdraft velocity occuring in the upper-middle part of the cloud was 4.44 ms−1. The temperature inside the cloud was higher than the outside, with their difference being positively correlated with the cloud water content. The temperature lapse rate inside the cloud was about −6.5°C km−1. The liquid water content and droplet effective radius (Re) increased with increasing height. The cloud droplet number concentration (Nc) increased first then decreased, peaking in the middle and lower part of the cloud, the average values of Nc and Re were 767.9 cm−3 and 5.17 μm, respectively. The cloud droplet spectrum had a multi-peak distribution, with the first appearing at ∼4.5 μm. SS in the cloud first increased then decreased with height. The maximum SS is ∼0.7% appearing at ∼3,800 m. The conversion rate of intra-cloud aerosols to cloud droplets was between 0.2 and 0.54, with the ratio increasing gradually with increasing height. The cloud droplet spectral dispersion and Nc were positively correlated. The aerosol indirect effect (AIE) was estimated to be 0.245 and 0.16, based on Nc and Re, respectively. The cloud droplet dispersion mainly attenuated the AIE, up to ∼34.7%.

Field report: Deployment of a fleet of drones for cloud exploration

Drones are commonly used for civil applications and are accessible to those with limited piloting skills in several scenarios. However, the deployment of a fleet in the context of scientific research can lead to complex situations that require an important preparation in terms of logistics, permission to fly from authorities, and coordination during the flights. This paper is a field report of the flight campaign held at the Barbados Island as part of the NEPHELAE project. The main objectives were to fly into trade wind cumulus clouds to understand the microphysical processes involved in their evolution, as well as to provide a proof of concept of sensor-based adaptive navigation patterns to optimize the data collection. After introducing the flight strategy and context of operation, the main challenges and the solutions to address them will be presented, to conclude with the evaluation of some technical evolution developed from these experiments.

CLOUD DROP SPECTRA IN MARITIME AND INLAND REGIONS

Measurements o f clo ud drop ..ire spectra on non-preci pitating cumulus clouds, 1·2 km thick,were made at differe nt levels o ver the Arabian Sea (maritime) and over r une (inland) regio n during the end ofthe summer monsoo n seasons of 1973, 1974 and 1979.The macimurn size of clo ud drops for the. Arabian Sea generally increased with height. while that for run eJiJ not show a systematic change with height. At bot h the local ions. the total concentration o f drops decreasedwith height. The maritime dist ributions were bimodal at all levels while those o..-er Punc were usually unimodal.The average values of liquid water content. mean vo lume diameter. dispersion and conccnt rarion of drops withdiameter > 50 «m were a lin le greater and total concentration a little smaller over the maritime region as ' om'pared to those over inland. The co ncentrations of drops with diameter < 14 ,...m and those > 78 I'm and thema ximum ~ i 7e were greater over Pune than o..er the sea. The ..'a riarions in cloud drop spectra and the clo udphysical parameters over beth the locations are discussed.Kc) words - Cloud drop size spectra, Drop co ncentration,

Deployment of the C-band radar Poldirad on Barbados during EUREC⁴A

The German polarimetric C-band weather radar Poldirad (Polarization Diversity Radar) was deployed for the international field campaign EUREC4A (Elucidating the role of clouds–circulation coupling in climate) on the island of Barbados where it was operated from February until August 2020. Focus of the installation was monitoring clouds and precipitation in the trade wind region east of Barbados. Different scanning modes were used with a temporal sequence of 5 min and a maximum range of 375 km. In addition to built-in quality control performed by the radar signal processor, it was found that the copoloar correlation coefficient ρHV can be used to remove contamination of radar products by sea clutter. Radar images were available in real time for all campaign participants and aboard research aircraft. Examples of mesoscale precipitation patterns, rain rate accumulation, diurnal cycle, and vertical distribution are given to show the potential of the radar measurements for further studies on the life cycle of precipitating shallow cumulus clouds and other related aspects. Poldirad data from the EUREC4A campaign are available on the EUREC4A AERIS database: https://doi.org/10.25326/218 (Hagen et al., 2021a) for raw data and https://doi.org/10.25326/217 (Hagen et al., 2021b) for gridded data.

Wolkenverfolgung: Vom Experiment zur Realität

&lt;p&gt;Die Wolkenverfolgung ist die einzige M&amp;#246;glichkeit zur Beobachtung der zeitlichen Entwicklung von Wolken und zur Quantifizierung der Ver&amp;#228;nderung ihrer physikalischen Eigenschaften w&amp;#228;hrend ihrer Lebensdauer (Seelig et al., 2021). Der Schl&amp;#252;ssel dazu sind zeitaufgel&amp;#246;ste Messungen von Instrumenten an Bord geostation&amp;#228;rer Satelliten. Experimente mit atmosph&amp;#228;ren&amp;#228;hnlicher Konfiguration treiben die Entwicklung von Messmethoden und Alghoritmen unter Laborbedingungen voran. Heutzutage ist es z.B. m&amp;#246;glich zweidimensionale, zeitlich und r&amp;#228;umlich hochaufgel&amp;#246;ste Geschwindigkeitsfelder auf Basis der Verschiebung kleinster Partikel zu messen (Seelig and Harlander, 2015; Seelig et al., 2018). Die Methodik der Partikelgeschwindigkeitsmessung dient als Anfangsbedingung zum Verfolgen dieser Partikel und kann auf troposph&amp;#228;rische Wolken angewendet werden. Diese Pr&amp;#228;sentation stellt die Analogie von Experiment zur Realit&amp;#228;t vor, beschreibt das Verfahren der Partikelgeschwindigkeitsmessung und die Anwendung auf Daten geostation&amp;#228;rer Satelliten.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Literatur:&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;Seelig, T., Deneke, H., Quaas, J., and Tesche, M.: Life cycle of shallow marine cumulus clouds from geostationary satellite observations, J. Geophys. Res.: Atmos., 126(22), e2021JD035577, https://doi.org/10.1029/2021JD035577, 2021.&lt;/p&gt; &lt;p&gt;Seelig, T., Harlander, U., and Gellert, M.: Experimental investigation of stratorotational instability using a thermally stratified system: instability, waves and associated momentum flux, Geophys. Astrophys. Fluid Dyn., 112, 239-264, https://doi.org/10.1080/03091929.2018.1488971, 2018.&lt;/p&gt; &lt;p&gt;Seelig, T. and Harlander, U.: Can zonally symmetric inertial waves drive an oscillating zonal mean flow?, Geophys. Astrophys. Fluid Dyn., 109, 541-566, https://doi.org/10.1080/03091929.2015.1094064, 2015.&lt;/p&gt;

Vertical development of precipitation echoes from cumulus clouds near Calcutta during the post-monsoon season

Vertical development of precipitation echoes from cumulus clouds near Calcutta during the post-monsoon season of 1956 was studied by using a Decca Type.41 3-cm radar installed at the Meteorological Office at Dum Dum airport. It has been shown that the origin of the first precipitation echoes were below the freezing level in most cases. The rate of growth of the precipitation echoes was found to be comparable with that found in USA.A condensation coalescence mechanism has been suggested for the formation of rain from these clouds.