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Shallow cumulus convection in the Tropical Atlantic Ocean: Controls, responses, and mechanisms

Differences in the representation of shallow cumulus convection and cloudiness are a leading contribution to diversity in climate model sensitivity and climate projections. We propose to use numerical modeling of trade-wind cumulus from large eddy simulations to regional modeling, analysis of field observations, satellite data, and of reanalysis products to address the coupling between convective mixing, surface turbulent fluxes, and low-cloud radiative effects in largescale subsidence regimes. The modeling will be tightly integrated with the Atlantic Trade-wind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC, US) and the Elucidating the Role of Clouds-Circulation Coupling in Climate (EUREC4A, Europe) Ocean-Atmosphere field campaigns. We will examine the controls on the properties, statistics, and organization of shallow cumulus convection and cloudiness, and its response to ocean and atmosphere mean state and variability. Emphasis will be placed on processes that are unresolved or unrepresented in climate models and which contribute to diversity and biases in climate simulations and model-derived climate sensitivity.
The objectives are:
• Quantification of the mean state and statistical properties of shallow cumulus convection in response to atmospheric and oceanic mean state, and atmospheric and oceanic spatiotemporal variability
• Quantification and characterization of mesoscale organization, its response to oceanic and atmospheric mean state and variability, and its role for the properties of trade cumulus convection and cloudiness
• Characterization of feedback mechanisms between the atmosphere and the ocean that codetermine ocean-atmosphere interactions and the properties of trade cumulus convection and cloudiness
Modeling will be carried out in close concert with the European and US assets to be brought to the field: aircraft observations (the NOAA P-3 and NOAA G-IV, the French ATR-42 and the German HALO), shipborne measurements (the NOAA R/V Ronald H. Brown and up to three European ships), and satellite remote sensing.
The proposed work will further NOAA’s long-term climate research goals and the goals of the NOAA CVP program by enhancing the understanding of the climate system and its predictability in a number of ways. First, it will elucidate our fundamental understanding of the trade-wind cumulus system by focusing on the meteorological/ocean surface factors that control cloud field properties (e.g. cloud fraction, condensate, and precipitation) through comprehensive modeling and observations at a broad range of scales (10s to 100s of km). Second, the extent to which variance in these factors at the sub GCM grid-scale affects these cloud field properties will reveal the model grid mesh required to adequately resolve them. Third, the model output and analysis of observations will together provide a wealth of data to inform development of GCM subgrid cloud and precipitation schemes for years to come.

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