From Sugar to Flowers: A Transition of Shallow Cumulus Organization During ATOMIC. (11th October 2021)

• Record Type: Journal Article
• Authors: Narenpitak, Pornampai; Kazil, Jan; Yamaguchi, Takanobu; Quinn, Patricia; Feingold, Graham
• Is Part Of: Journal of advances in modeling earth systems. Volume 13:Number 10(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-11
• Subjects: shallow cumulus -- cloud organization -- cloud and aerosol -- Lagrangian large eddy simulation -- mesoscale circulation -- large scale subsidence; Geological modeling -- Periodicals; Climatology -- Periodicals; Geochemical modeling -- Periodicals; 551.5011
• DOI: 10.1029/2021MS002619
• Languages: English
• ISSNs: 1942-2466

Abstract

Abstract: The Atlantic Tradewind Ocean‐Atmosphere Mesoscale Interaction Campaign (ATOMIC) took place in January–February, 2020. It was designed to understand the relationship between shallow convection and the large‐scale environment in the trade‐wind regime. A Lagrangian large eddy simulation, following the trajectory of a boundary‐layer airmass, can reproduce a transition of trade cumulus organization from "sugar" to "flower" clouds with cold pools, observed on February 2–3. The simulation is driven with reanalysis large‐scale meteorology, and in‐situ aerosol data from ATOMIC and its joint field study EUREC 4 A. During the transition, large‐scale upward motion deepens the cloud layer. The total water path and optical depth increase, especially in the moist regions where flowers aggregate. This is due to mesoscale circulation that renders a net convergence of total water in the already moist and cloudy regions, strengthening the organization. An additional simulation shows that stronger large scale upward motion reinforces the mesoscale circulation and accelerates the organization process by strengthening the cloud‐layer mesoscale buoyant turbulence kinetic energy production. Plain Language Summary: Fair‐weather shallow clouds have different sizes and cloud properties. A field study called the Atlantic Tradewind Ocean‐Atmosphere Mesoscale Interaction Campaign (ATOMIC) and Elucidating the Role of Clouds‐Circulation Coupling in Climate (EUREC 4 A) was designed to further understand the properties of these clouds. On February 2–3, very small and shallow "sugar" clouds grow into wider and deeper "flower" cloud clusters, no more than 3 km high. The clear spaces between the clouds expand. This study finds that local air circulation is responsible for making the moist and cloudy areas moister, and dry and cloud‐free areas drier, enabling a process responsible for this transition. The large‐scale vertical winds modulate the rate and strength of this process, which occurs locally at smaller scales. Key Points: Lagrangian large eddy simulation can reproduce the transition of shallow cumulus organization from sugar to flowers observed on February 2–3, 2020 during Atlantic Tradewind Ocean‐Atmosphere Mesoscale Interaction Campaign While large‐scale upward vertical wind deepens the cloud layer, mesoscale wind renders moist areas moister assisting cloud organization Stronger large‐scale upward motion strengthens the mesoscale circulation and accelerates the sugar‐to‐flowers transition process