POPC4OM: Understanding population controls on cloud-circulation coupling based on observationally-constrained modeling
Final Report Abstract
Low level cumulus cloud fields persistently cover substantial areas in the marine subtropical Trade wind regions, and hence play an important role in Earth's climate system. Over the years systematic biases involving the representation of such cumulus cloud fields in weather- and climate models have been identified. The associated feedback mechanisms between such cloud fields and climate are still poorly understood, in particular their coupling to the larger-scale environment and the role played by their spatial structure and organization. Recent meteorological field campaigns in the Atlantic Trade Wind region have provided a wealth of new data. During the EUREC4A field campaign (ElUcidating the Role of Clouds- Circulation Coupling in ClimAte) near Barbados in Spring 2020, cumulus cloud fields and their larger-scale environment were sampled by modern airborne measurement platforms including the High Altitude and LOng-range research aircraft (HALO). The POPC4OM project aims to combine these unprecedented datasets with dedicated high-resolution Large-Eddy Simulations (LES) on High-Performance Computing (HPC) clusters. The first research objective is to design realistic simulations based on HALO dropsonde measurements, to anchor them in reality. The second objective is to thoroughly evaluate these simulations against independent cloud measurements, using both HALO and satellite datasets. The third objective is to use the model results to gain more insight into how cumulus population dynamics affects the transformation of the air mass in which they are embedded, focusing on the role of spatial organization and its evolution over time. A first key insight followed from the detailed model evaluation against high-frequency GOES satellite data. We find that defining features of the spatial organization of the cloud field along the multi-day Trade wind trajectory are well reproduced by the model. The second key insight is the identification of a particular form of nocturnal cloud organization at meso-scales in the upstream areas of the low-level Trade wind flow. This previously unknown form of organization, called “nocturnal mini-flowers”, fundamentally differs from the larger and better-known “flower” clouds encountered further downstream near the EUREC4A target area. A distinct difference is the absence of cold pool dynamics, expressed as a distinct gap in the horizontal energy spectrum of thermodynamic state variables in the atmospheric boundary layer. The outcome of the POP4COM project has wider implications. Firstly, they promote the use of field campaign data in high-resolution realizations of key atmospheric processes in our climate. Secondly, they increase our knowledge base on cloud transformations in the subtropics, inspiring follow-up research and creating new scientific opportunities for untangling the complex interactions between clouds and climate.
Publications
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2nd Workshop on Cloud Organization (WCO2, Utrecht, May 2022. Diurnal signals in flower cloud organization in the upstream Tradewind regions during EUREC4A
Salima Ghzayel et al.
