Simulation For The Thermodynamics Of Subsurface Warm Water In The Arctic Ocean

Subsurface Warm Water (SWW) is a frequently observed phenomenon in most part of Canadian Basin, which presents a temperature peak of -0.7℃under sea ice at the depth of 20 m. Researches show that the SWW is formed locally without external water source. A thermodynamical coupled sea ice-upper ocean column model is developed in this paper to examine the thermodynamics of SWW, changes of sea ice, and heat exchange between air and ocean.Annual sea ice thickness and heat exchange on air-sea interface in the central region of the Arctic Ocean are simulated by the coupled model. The results are consistent with the previous studies, which show the model is trusty. Downward longwave flux and solar flux are proved to be most important to ice thickness and lead fraction by studying their contributions, other thermodynamic factors such as air temperature and specific humidity have less influence than longwave and solar flux. The results also show that ice thickness is almost linear with forcing variations, but lead fraction is not as so. In addition, numerical experiments find that the thinner ice is, the greater lead fraction is, and the stronger air-sea heat exchange is.Using this model, the SWW is successfully simulated, consistent with observed results. The mechanism to form the SWW is proved to generate by both solar radiation heating and surface cooling. It is verified that the solar radiation is the dominant energy source for SWW, meanwhile long-wave flux, air temperature, and atmospheric humidity play an important role in determining the relative intensity of SWW. As the solar energy would be obstructed from thick ice, SWW is formed only when thin ice, ice edge, leads or undisturbed open water occurs.Numerical experiments also find that SWW is closely related to vertical eddy diffusivity. A vertically varied eddy diffusivity is fitted by the observed temperature to simulate the typical sharp peak of SWW. It is about 5.0×10-3 m2/s just under sea ice, whereas decreases down to 1.0×10-6 m2/s at peak of SWW caused by the stratification of halocline.This eddy diffusivity is also the main reason why SWW is not interfered by summer Pacific halocline water, and why they appear at the same time at the different depths. A quantitative relationship between SWW and penetrating solar flux is restablished on above results, on which a heat feedback to speed SWW is presented.