Sea Ice Dynamics Induced by External Stochastic Fluctuations
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Pure and Applied Geophysics
Sea Ice Dynamics Induced by External Stochastic Fluctuations DMITRI V. ALEXANDROV,1 IRINA A. BASHKIRTSEVA,1 ALEXEY P. MALYGIN,1 and LEV B. RYASHKO1 Abstract—The influence of stochastic fluctuations in the atmosphere and in the ocean caused by different occasional phenomena (noises) on dynamic processes of sea ice growth with a mushy layer is studied. It is shown that atmospheric temperature variances substantially increase the sea ice thickness, whereas dispersion variations of turbulent flows in the ocean to a great extent decrease the ice content produced by false bottom evolution. Key words: Sea ice, mushy layer, false bottom, stochastic fluctuations, nonlinear dynamics.
1. Introduction Recent studies of the ice cover changes have refocused attention on the correct description of local processes that have large scale consequences. For instance, the growth and decay of sea ice in the Polar Regions is the high-latitude equivalent of the evaporation-precipitation cycle in the remainder of the world’s oceans (AAGARD and CARMACK, 1994). One of the important contributions of the ice evolution is connected with cracks in the perennial ice cover, known as leads. These transient fissures attract scientific attention because they provide a thermal conduit through which heat- and radiative-transfer processes are enhanced tremendously, relative to the thick pack ice that surrounds them. The thermal importance of leads was put in context by BADGLEY (1966), who showed that during winter the atmospheric heat flux from rapidly freezing leads can be several orders of magnitude larger than over perennial sea ice. He emphasized the large-scale implications of leads by arguing that they need
1 Department of Mathematical Physics, Ural Federal University, Ekaterinburg 620000, Russian Federation. E-mail: [email protected]
occupy only 1 % of the area of the ice cover in order to dominate the heat exchange from the ocean to the atmosphere. In the Arctic winter, the relatively warm water in leads is exposed to the cold air above it. As a result, a thin veneer of ice rapidly forms across an exposed lead. After 1 day’s growth the ice layer is about 10 cm deep, which is still thin compared with the surrounding ice, which is typically 1–2 m thick. The field observations show that the heat loss through leads can be up to 300 Wm-2, or 15 times that from the surrounding ice (The LEADEX Group, 1993). Although leads occupy less than 10 % of the surface area, they are responsible for roughly half of the total oceanic heat loss (The LEADEX Group, 1993). It is known that sea ice growth can be sufficiently fast, so that its depth 8–10 cm can be attained in the first 24 h (WETTLAUFER, WORSTER and HUPPERT, 2000; PEROVICH and RICHTER-MENGE, 2000). A rapid growth of such young sea ice produces the greatest heat flux, so the role of brine drainage on the phase evolution is significant in determining the overall heat budget (see, among others, WETTLAUFER, WORSTER and HUPPERT, 1997; ALEXANDROV and MALYGIN, 2011a). Since
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