MECHANISMS OF INTERACTION BETWEEN MESOSCALE OCEAN EDDIES AND SEA ICE IN HIGH-RESOLUTION ICE-OCEAN COUPLED MODEL OF THE LAPTEV SEA IN SUMMER

摘要

Precise ice distribution prediction is one of key issues to realize safe and efficient navigation in the Northern Sea Route (NSR). Results of high-resolution (2.5km) hindcast computation (De Silva, 2015) have shown good agreement with observational ice distribution, which has motivated us to search for possible factors driving the sea ice variability in NSR using numerical model. We have found that mesoscale eddy production is one of the main factors responsible for sea ice variability in the Laptev Sea marginal ice zones. A three-dimensional high-resolution ice-ocean coupled model is used to investigate the eddy generation mechanisms. The model is designed to represent a typical condition for the summertime Laptev Sea mixed layer. Eddy generation due to ice-ocean interaction is discussed in details; a wind stress is larger over the ice than that on open water and induces Ekman pumping and suction, which produce dipole eddy motions. Vertical motions associated with the dipole eddies lead to deep vertical mixing and the subsequent melting of the ice. The dipole eddies generated by barotropic instability is further enhanced by vertical mixing and freshwater input due to sea ice melt. Those eddies are important to exchange the heat across the ice edge and to meandering of ice edge. Numerical sensitivity experiments suggest that the horizontal scale of generated eddies depends on the surface forcing. Also, these small-scale features are not modeled well with horizontal grids coarser than approximately 5 km.