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3rd HyMeX workshop 1-4 June 2009 Heraklion (Gournes), Crete-Greece

Air-Sea Heat Fluxes estimation over the eastern Mediterranean based on HCMR's Poseidon buoy network

Vassilis Papadopoulos (Hellenic Centre for Marine Research, Local Office of Achaia); Themis Chronis

Air-sea interaction includes a wide range of continuously evolving phenomena with significant impacts on key atmospheric and oceanic processes. Air-sea interaction includes mass and momentum interchange. Evaporation, precipitation and absorption of atmospheric gases (O2, CO2) by the ocean are included in the mass interchange while heat fluxes and wind stress define the momentum transfer. The air-sea heat interchange plays a proven key role as:
- A basic input in the oceanic and atmospheric models
- A critical climate regulator
- The main factor of ocean heat content
- A driving force for sea water masses formation and deep water convection
- A climate change index
On a global scale, different data sources targeting the air-sea heat fluxes estimation have been adopted (Josey et al, 2006). These include: a) data from voluntary observing ships and oceanographic buoys b) reanalysis methods (e.g. ECMWF, NCEP-NCAR), c) satellite observations d) Merged techniques involving satellite observations and model reanalysis. By the time being, fluxes emanating from datasets of the first of the above categories are characterized as “quality research fluxes”. They are generally accepted as the reference for any evaluation of fluxes coming from the rest sources The Hellenic Centre for Marine Research (HCMR) has undertaken the employment of the POSEIDON in the production of air-sea heat fluxes estimates. Such process requires the following key variables: total cloud coverage, specific humidity, air temperature, sea surface temperature, wind speed and atmospheric pressure. For the turbulent components, the heat budget estimation additionally utilizes the
significant wave height. From the aforementioned variables only the first two are not directly acquired from the POSEIDON buoys. Presently, the total cloud coverage originates from the extended Hellenic National Meteorological Service ground network. Additional cloudiness information is also acquired by current satellite platforms such as MSG-II and AQUA/TERRA. Regarding specific humidity, the operational constellation of SSM/I is used (Bentamy et al, 2003).
For the calculation of the heat budget components as well as the net heat flux, we employ the bulk formulae. For the short wave radiation the Reed formula (Reed, 1977, Seckel & Beaudry, 1973) has been adopted while an attenuation factor due to atmospheric aerosol concentration is applied (Tragou & lascaratos, 2003). The Bignami formula (Bignami et al, 1995) is used for the long wave radiation and this formulation is widely used for the Mediterranean Sea region. Finally, the COARE algorithm (v3.0) is implemented for the production of the heat budget turbulent components (Fairall et al, 2003).
Each POSEIDON-based heat flux retrieval is limited to the specific buoy mooring site. Further comparison is evaluated against other products such as the global air-sea interaction atlas of National Oceanographic Centre (UK) (Josey et al, 1998) and the gridded fluxes from ECMWF and NCEP-NCAR. The future POSEIDON expansion and proper calibration of the proposed method will promote future retrievals and will include other parts of the Mediterranean (e.g. the Levantine and Ionian Seas).