The relationship of trade-wind cumulus and its mesoscale organization to the larger-scale environment of the Northwest Tropical Atlantic (ATOMIC)

The trade-wind region is important to global climate because its governing large-scale circulation 1) evaporates water vapor off of the ocean surface that is then fed into the precipitating ITCZ, and 2) frequently exposes the low-altitude boundary layer clouds to space, allowing a mild cooling of the Earth’s climate through radiation over a large region. The low altitude cloud fraction can fluctuate dramatically despite minor synoptic variability, and organize into characteristic mesoscale patterns (e.g., popcorn cumuli, cloud streets, mesoscale arcs) that in part reflect the influence of precipitation. The cloud fraction and its relationship to these underlying processes is an important metric for models at a wide range of resolutions. The relationship to the free-troposphere mixing serves to motivate the EUREC4A project; the cloud fraction as a function of the cloud mesoscale organization is also still not well-known. These relationships are difficult to derive from modeling experiments, because of sensitivity to the microphysical and mixing parameterizations.
This proposal seeks to improve our understanding of how the cloud fraction in the trade-wind regime relates to its organizing processes through involvement in and analysis of observations from ATOMIC: the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign. As part of ATOMIC, three unique NOAA resources have been requested, namely the Research Vessel the Ronald H. Brown, along with the NOAA P-3 and G-4 planes. Zuidema will deploy several instruments providing cloud, precipitation, and air/sea temperatures upon the R/V Brown, namely a W-band Doppler zenith-pointing radar, a microwave radiometer, disdrometers, and a hyperspectral MAERI for SST, analyze these measurements and integrate them with other ship-board measurements, including aerosols. GOES-16 satellite data will be collected and analyzed for cloud mesoscale organization, with the analysis from other years providing context for the ATOMIC time period. Dropsonde and radar measurements from the research aircraft will provide spatial context for the ship-board measurements, and flight paths will also be designed to optimize opportunities for Lagrangian sampling. This includes developing daily forecast air mass trajectories based on the positions of the NOAA/EUREC4A research platforms. Aircraft microphysical measurements will aid assessments of aerosol-cloud interactions.
The analysis will build on and contribute to collaborations with C. Fairall (NOAA ESRL) on deployment planning and data analysis, G. Feingold (NOAA ESRL) on integrating observations into modeling efforts, S. de Szoeke (OSU) on the radiosonde analysis and boundary layer energetics, E. Thompson/J. Thomson (UW APL) and C. Clayson (WHOI) on ocean-air interactions and connecting atmospheric behavior to ocean mesoscale variations, and T. Quinn (NOAA PMEL) on aerosol-cloud interactions. Collaboration with EUREC4A scientists is expected, including on developing a ‘best-estimate’ of large-scale forcing.
Broader Impacts and Relevance to CVP program: The curated, analyzed data will form a long-term legacy dataset that will serve as a basis for subsequent process model studies and large-scale model evaluation. This research will enhance process-level understanding of the ocean-atmosphere interactions and atmospheric boundary layer processes governing the expansive trade-wind region. This region remains poorly modeled within climate models, to a large degree because the low clouds and their link to the troposphere have not been as comprehensively observed as will occur through the EUREC4A/ATOMIC programs.