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Observing and Understanding Upper-Ocean Processes and Shallow Atmospheric Convection in the Tropical Atlantic Ocean

Above most of the oceans, liquid clouds of a few thousand meters or less drive mixing in a process called shallow convection in the atmospheric boundary layer (ABL). The warm clouds dominate the ocean’s area coverage and may strongly influence weather on seasonal to sub-seasonal time scales. Shallow convection exerts an important influence on sea surface temperatures (SSTs) and salinity by moderating the air-sea exchanges of energy and moisture and represent a ‘major source of uncertainty in projections of future climate’. The interaction between shallow convection and the ocean’s surface layers is a two-way street: though shallow convection influences SSTs, shallow convection is itself controlled to a large extent by SST and air-sea fluxes, which are mediated by processes within the ocean, especially Oceanic Barrier Layers (OBL) and mesoscale ocean eddies. OBL are near-surface layers created by low salinity waters and embedded in the ocean mixed layer. OBLs tend to decouple the ocean mixed layer from surface momentum fluxes, which facilitates subsurface warming as short wave radiation penetrates to the base of the OBL. Both eddies and OBL can influence weather and climate patterns.
In this project we propose to investigate the structure and dynamics of shallow convective boundary layers and their coupling to oceanic variability and mixing via ship-based surface flux and atmospheric boundary layer observations during the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC). We propose continuous sampling aboard a research vessel that operates east of Barbados during the ATOMIC field program. The observing systems will be similar to those deployed in NOAA’s recent DYNAMO and PISTON studies. The ship will sample the atmosphere and ocean in the context of a larger array of ships and aircraft in cooperation with the Elucidating the role of cloud-circulation coupling in climate (EUREC4A) field program. Using in situ sensors, unmanned aircraft (UAS), and vertically-pointing Doppler remote sensing, we will measure and characterize mesoscale and synoptic variability in the surface fluxes, ABL and cloud turbulence as convective systems pass over the ship. The large-scale forcing will be determined by a combination of ship-launched balloon soundings and aircraft dropsondes associated with the larger ATOMIC/EUREC4A programs.
We expect to work closely with P. Zuidema (U. Miami), S. de Szoeke (OSU), G. Feingold (NOAA/CSD) and P. Sullivan (NCAR) on LES modeling of the oceanic and atmospheric boundary layer and ABL-cloud interactions. The combination of LES and UAS plus radar-lidar velocity profiles will allow us to examine local gradient vs non-local (mass flux) boundary-layer flux profile parameterizations. We will coordinate with PMEL (Quinn) on UAS and aerosols observations. We will work with E. Thompson (APL-US) and J. edson (WHOI) on connecting atmospheric forcing with oceanic response. We will coordinate with the NOAA P-3 aircraft to set the mesoscale context of the ship observations. The P-3 will deploy dropsondes and AXBT (S. Chen NRL) and it will host the PSD Airborne Doppler W-band radar and the WSRA ocean surface wave radar.

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