Indirect Determination of Surface Heat Fluxes in the Northern Adriatic Sea via the Heat BudgetR. P. Signell, A. Russo, J. W. Book, S. Carniel, J. Chiggiato, H. Perkins, J. Pullen, J. D. Doyle 2004 ROMS/TOMS European Meeting
Motivations • Many processes in the Northern Adriatic Sea are strongly affected by surface forcing (i.e., production of one of the densest water in the Mediterranean) • Its coastal features, shallowness and surrounding complex orography critically stress the correctness of our ABL parameterizations and surface fluxes estimates, eventually degenerating model solutions • Surface fluxes are poorly measured and their value at a basin level in the Adriatic is still an open issue. …therefore… … we used a model-based experiment to infer what the fluxes should have been (period fall 2002 – winter 2003), comparing changes in the heat content in the model with those estimated using observations
Hypothesis • Shallow water, strong surface cooling and vertical mixing result in homogenization of the water column • this allows to work with a 2D “vertically averaged temperature” field. (to be estimated via collected data) • Although with negligible stratification, the use of a 2D averaged temperature leads to small bias (to be evaluated). • we need to compute somewhat error bars associated to the estimates • *When* the lateral advection of heat outward/inward the basin is playing a minor role, changes in the heat content can be related to exchanges at the air-sea interface • we run the model to check when this is supposed to be applicable
ADRIA 2002 data Transect bounding our domain
Comparison SST data vs moorings Full mixing conditions hypothesis: SST, surface and bottom temperature revealed similar
Heat content by means of measurements • Selection of clear sky –wind dominated days in order to have good SST images • Check if data suggest nearly full mixing • Estimate of the heat content: • Lower bound: SST - OA (SST-SBT) • Upper bound: SST – OA (SST-SSTBULK) • Reference temperature = mean between the two bounds
Limited Area Model Italy Non-hydrostatic 7 Km horz resolution, 3-hourly Operational forecast twice a day 00+03…+12, 12+03…+12 GMT 48 rivers, daily runoff: measured or climatology Full ABL Open Boundary: Tidal elevation and currents Model Set-Up Grid 160x60 variable resolution up to 3 Km to the North Initialization: spun up at rest with temperature and salinity fields obtained by OA on data collected during the cruise ADRIA 02 (late sep 2002) Length of the run: Sep 02 -- > Jun 03
Comparison between ROMS and LAMI fluxes • LAMI turbulent fluxes are always more negative • COAMPS turbulent fluxes show similar values as LAMI • This is due to different parameterizations of fluxes, • not to the SST used by ALAMs (we tested) Question: Which one is realistic? Is at least one of them realistic?
Conclusions • by carefully choosing nearly cloud-free images during periods of nearly uniform mixing, we computed heat content estimates of the Northern Adriatic Sea by means of the SST and in-situ measurements, during 5 different days between November 2002-February 2003 (planning to have more); • model results indicate that, in the period investigated, the heat budget is dominated by surface fluxes; • the total heat fluxes resulting from the ROMS/LAMI simulation fall within the reasonable bounds of total heat fluxes determined by data in each of the 4 intervals studied, indicating that using ROMS SST with LAMI meteo parameters and its own bulk formula (Fairall, 1996) is producing results as good as can be determined by data; • care must be taken when computing these estimates and associated errors (feedbacks are welcome!!!), depending then very much on the nature and distribution of available data; • LAMI (and COAMPS) turbulent fluxes are too high, indicating a suboptimal bulk flux parameterization over the ocean during strong forcing events; care must be taken when using directly model derived turbulent fluxes.