Reconciling the surface drag and enthalpy coefficients using in-situ and tank measurements.
Abstract
Approved for Public ReleasePredictions of coupled models depend heavily on the fluxes of momentum and enthalpy across the air-sea interface. Current parameterizations of these fluxes, mostly based on Monin-Obukhov scaling, appear to have significant errors. Morerobust schemes including the effects of wave roughness, of wave directions relative to the wind and of spray, are likely needed, but there are currently insufficient data to formulate such schemes. The proposed project will measure and estimate the exchange coefficients under tropical cyclones (TC) and over shoaling waves in shallow water, as well as under similar but controlled laboratory conditions in the UM SUSTAIN wind/wave facility. Comparison of the field and previous laboratory measurements will be used to assess existing and proposed flux parameterizations using the oceanic response as a tracer of momentum and enthalpy fluxes. An overall goalis to compare the variations in exchange coefficients found in these three very different environments, TC, shoaling waves and SUSTAIN.The TC component aims to make high-quality enthalpy flux measurements above 35 m s-1 including simultaneous drag and enthalpy flux estimates from both sides of the air-sea interface that can be used to test model predictions that the air and water side fluxes differ due to transport of wave momentum. It aims to test a new wave-based drag parameterization and estimate the importance of spray to enthalpy fluxes. Air-deployed profiling EM-APEX floats and spotter buoys will measure fluxes from changes in the ocean complemented by in-situ measurements from atmospheric and oceanic expendables from the NOAA WP-3D and remote sensors on the aircraft. Winds, directional waves and atmospheric profiles will be measured from aircraft using operational passive microwave, wave radar and dropsonde data. We anticipate ocean-side measurements by ten EM-APEX floats in two storms in the Western Atlantic during the 2025 and 2026 seasons and additional floats to be deployed in the western Pacific typhoons in 2027 from the USAF WC-130J. The coastal component will measure the expected, but poorly measured, increase in drag and enthalpy coefficients over shoaling. Wave buoys and moorings will measure directional wave spectra and surface meteorological conditions (temperature, humidity, pressure, waves, etc). Coastalradars, sponsored by SECOORA, will measure ocean currents and waves and provide regional context. We anticipate measurements in early 2028 in the South Atlantic Bight. The UM SUSTAIN tank component will (1) utilize previous experimental results in conceptualizingphysical processes controlling the drag and enthalpy coefficients under a wide range of wind/wave conditions including those of TC;and (2) quantify the variability of broadband wave spectra in the tank (i.e. wave steepness, directional spreading) that has not been fully explored and its net effect on the drag. The proposed experimentation focuses on explaining the differences between laboratory (saturating) and field (decreasing) measurements of drag coefficients with increasing extreme winds and the field observations of decreased drag coefficient in the complex wave fields (left-side) of storms, and estimating the relative contribution of spray toenthalpy fluxes. Measurement techniques will build upon developments and insights from recent projects and cover regimes overlapping with those from the field campaigns. The measurements will include turbulent eddy-covariance heat, moisture, and momentum fluxes, wave spectra at multiple locations and from redundant sensors, and high-speed shadow-imaging of spray concentrations. The proposed research will also collaborate with the MURI team led by the University of Notre Dame. Instrumentation will be proposed through a DURIP proposal in FY25. The proposed research will educate and train students and a post-doctoral fellow.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142412598
Entities
People
- Lynn Shay
Organizations
- Office of Naval Research
- United States Navy
- University of Miami