The Physical Constraint On The Air-sea Heat Flux Based On The Heat Budget Analysis

Air-sea heat flux is of importance and significance for the air-sea interactionstudies. The thermal perspective of heat flux contributes directly to the global climatechange. However, the previous studies mainly focused on the parameterization of theheat flux, the observations of the meteorological variables at the air-sea interface andtheir inter-comparisons. The global and regional heat flux quantification andvariability is still poorly understood.Based on the integrated heat budget analysis, this paper shows how much air-seanet heat flux should go into the ocean inversely from the heat budget balance of theocean. The nine climatological heat fluxes （observations, objectively analyzed andreanalyses） are diagnosed by the constrained results, which can provide the possibilityfor the heat flux validation. Two main scientific questions are addressed, includingwhat the magnitude of the heat flux over the ice-free and ice ocean is and what therole of large-scale ocean and atmospheric circulations is for the global and regionalheat flux changes.Integrating the heat equation over the isotherm, the topography and the combinedisotherm and topography, this paper choose the global ice-free ocean, the ice ocean,the western Pacific warm pool, the Mediterranean Sea and the high-latitude waterformation as the testing bed. The heat fluxes over these regions will be inverselyobtained by the physical constraint under different integration cases. The mechanismsfor the heat fluxes associated with the climate events are also elucidated. The mainresults of this paper are as follows:1. With a constant vertical eddy coefficientk4v1.5×10-m2s-1, the climatologicalannual mean heat flux that goes into the ice-free ocean should be4.2Wm^-2approximately. The ice-free ocean is represented by the5oC isotherm here.According the heat balance of the whole ocean that all the mechanical forcingshould be transferred into internal energy, there should be a-44.8Wm^-2energyflux for the ice ocean approximately, releasing heat to the above atmosphere. However, large errors exist due to the physical assumption and data uncertaintyused in this paper. The heat exchange between the colder land and warmer oceanat high latitudes might contribute to the errors for the estimation. In the other cases,the mean air-sea net surface heat fluxes for the western Pacific warm pool definedby the28oC isotherm and whole Mediterranean Sea are27.9Wm^-2and-3.3Wm^-2,respectively. The mean ocean Hadley circulation transport is only2.1Sv (1Sv=1×10⁶m³s^-1 forced by the nine climatologies, which is far less than the previousestimate20+Sv.2. From the above constrained results, the OAFlux+ISCCP, NOCSv2.0, CFSR andMERRA are warmer biased between10Wm^-2and20Wm^-2, while ERA-40showscolder bias. Except for the Mediterranean Sea, the NCEP products also showcolder bias, but less than10Wm^-2. CORE.2and ERA-Interim show warmer biasover the global ocean but colder bias for the particular Pacific warm pool. Thecause for the common warm bias for all the climatologies is the underestimate ofthe high-latitude fluxes especially the turbulent heat flux （latent and sensible heatflux）. In the region near the ice edge, there should be more heat flux that should bereleased into the atmosphere. From the case of high-latitude water formation, theinsufficient meridional thermal difference cannot drive a volume flux of20+Sv,which confirms the warmer biased estimate of the nine climatologies.3. The role of large-scale ocean and atmospheric circulations for the globalintegrated surface heat flux is only an internal process, which can redistribute theglobal heat flux pattern and affect some local climate events. For example, thehigh-latitude turbulent heat flux corresponds to the global atmospheric oscillation,physically and statistically. The heat diffusion along the isotherm in the Pacificwarm pool is dominated by the velocity shear between the surface jet and thesubsurface Equatorial Undercurrent. Under the global warming background, thesea ice decreases dramatically at high latitudes. An estimate of a3-10Wm^-2heatanomaly is induced by the sea ice retreat when the ocean losses its shield. This candirectly trigger the ice cap warming in the troposphere. Thus, the feedback of theglobal warming and ice retreat will affect the heat flux, as well as the high-latitudedeep convection and enhance the climate process and cycles.