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Upper Ocean Observations of Upwelling Processes During Tropical Storm/Hurricane Isaac

This study focuses on the ocean response to tropical storm/hurricane Isaac through high-resolution oceanic and atmospheric measurements. The data includes analysis of upwelling due to wind-driven current divergence, current shear effects, sea surface temperature cooling, and potential storm feedback. Upwelling patterns were observed using probes, drifters, and ocean sensors during storm flights. Results highlight contrasting ocean responses, cyclonic wind stress impacts, and eddy interactions. The synthesized dataset aids in evaluating ocean-atmosphere interactions and improving operational models for efficient forecasting.

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Upper Ocean Observations of Upwelling Processes During Tropical Storm/Hurricane Isaac

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  1. Upper Ocean Observations of Upwelling Processes During Tropical Storm/Hurricane Isaac B. Jaimes, L. K. Shay, J. Brewster, R. Schuster (RSMAS/UM), M. D. Powell (HRD/NOAA) Acknowledge: HRD (Frank Marks) and NCEP, J. McFadden and Steven Paul (NOAA-AOC)

  2. Idealized ocean response carton that includes upwelling due to the divergence of the wind-driven current in the surface mixed layer, current shear central for mixing, SST cooling and, potential feedback to the storm. Leaman (1976)

  3. Key Air-Sea Parameter and Scales ( From Price , JPO, 1983) Rmax (Km) τ is from the HRD Hwind Product (Powell and Houston, MWR, 1996) Uh (m s-1) τ (Pa)

  4. High levels of oceanic heat content (OHC) were measured 9 days before the arrival of tropical cyclone (TC) Isaac. Successful probes during the P3 flight: 19 AXBT, 21 AXCTD, 5 AXCP, 8 dropsondes. • Altimeter-based surface geostrophic currents during the day that Isaac moved into the Gulf of Mexico.

  5. Expendable probes deployed during in-storm flights in Isaac

  6. In-storm flight (28 Aug, 4AM)

  7. Post-Isaac flight (30 Aug) Isaac Flight Summary • 58 AXBTs deployed in other 3 in-storm flights (97%) • 218 Ocean probes • overall success: 88% during six flights • Below are the T/S curves from XCTDs prior, during and after Isaac.

  8. Intensification to hurricane status over OHC gradients. Stronger hurricane winds occurred across OHC gradients.

  9. Contrasting ocean response in oceanic geostrophic features. Contrasting distribution of θE as a function of underlying oceanic features.

  10. vectors: Vg (altimeter-based) h20pre (m) Isaac moved over and intense geostrophic oceanic eddy field in the eastern Gulf of Mexico. During intensification to hurricane (28 Aug), the cyclonic curl of the wind stress extended over a region of more than 300 km in diameter (4Rmax to 5Rmax). contours: h20pre (m) • h20pre is from SMARTS (25 Aug) • τ is from Hwind (1030z, 28 Aug)

  11. contours: η = h20in - h20pre (m) h20pre (m) Contrasting upwelling (dashed contours) and downwelling (solid contours) regimes developed inside the region of cyclonic curl of the wind stress. • h20pre is from SMARTS (25 Aug) • h20in is from in situ P-3 data (28 Aug) • τ is from Hwind (1030z, 28 Aug) Vertical velocity associated with isopycnal displacements are a function both the geostrophic current vorticity and the wind stress (Stern, 1965; Jaimes nd Shay 2009): h20pre (m) (contours)

  12. Contrasting upwelling and cooling inside the region of cyclonic wind stress curl Downwelling Upwelling In-storm data is from the 28 August morning flight (during intensification to hurricane level)

  13. Isaac Response Summary Isaac data set has both atmospheric and oceanographic measurements across the entire Gulf (GPS sonde, expendables, drifters, moorings). Complete post-processing of the Isaac data set and analyze results for the • Upwelling (3-D) signals (Isaac slow mover over the shelf break); • Upper ocean response relative to the storm forcing; and • Integrate the AXBT (from the Demo Project), drifters and subsurface mooring data from GoMRI projects. Provide a synthesized data set to carefully evaluate ocean component of the coupled system and OSSEs. Operational models need temperature, current and salinity to evaluate oceanic and air-sea parameterizations used in coupled system.

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