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Effects of surface heterogeneity on the atmosphere over polar oceans

Effects of surface heterogeneity on the atmosphere over polar oceans. Timo Vihma Finnish Institute of Marine Research. Photo: H. Söderman. Heterogeneity is present in:. Material proper ties of the surface. Surface fluxes, temperature and albedo. Atmospheric boundary layer.

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Effects of surface heterogeneity on the atmosphere over polar oceans

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  1. Effects of surface heterogeneity on the atmosphere over polar oceans Timo Vihma Finnish Institute of Marine Research Photo: H. Söderman

  2. Heterogeneity is present in: Material properties of the surface Surface fluxes, temperature and albedo Atmospheric boundary layer Conductive heat flux through ice and snow material propertiesABL Ice thickness Turbulent heat fluxes Air temperature Surface temperature Snow thickness Air humidity Albedo Ice concentration Net shortwave radiation Cloud cover Floe and lead size Net longwave radiation Wind speed Freeboard ridges, and sastrugi Momentum flux

  3. Aspects related to surface heterogeneity: • 1. Turbulent fluxes over leads • 2. Vertical distribution of heat • rising from leads • 3. Area-averaged turbulent fluxes • and their parameterization • 4.Mesoscale evolution of ABL • 5.Effect of leads and polynyas on • large-scale circulation • 6.Cloud-radiative effects related • to surface heterogeneity Approximate number of journal papers in 1972-2002

  4. Horizontally interactive fluxes:the situation is less clear Mixture method: Mosaic method: Modified from Mahrt (1996, 2000, BLM) Blending height Top of equilibrium layer Zref Transition regime Homogeneous sub-areas Thermally-driven circulations Blending regime Scale ~ 1 km ~ 10 km ~ 40 km ---------- Leads --------------------- -------------- Polynyas, MIZ ------------------------------- mosaic or mixture method EM + parameterization of mesoscale transport ? Extended mosaic method

  5. Homogeneous sub-areas (poynyas, MIZ): •  mosaic method should be used because flow at the reference height is in balance with the local surface •  <a > and <V> not locally representative  possibilities for improvement suggested: • -        - calculate stability-dependent estimates for ai,w and Vi,w • -        -estimate ai,w - <a> on the basis of Si,w - <S> (Seth et al., 1994, JGR; Arola, 1999, JAS) • -        - use different reference heights for H and  (Essery, 1997, QJRMS) • Thermally-driven circulations (polynyas, MIZ): can transport significant amounts of heat but are not resolved by a large-scale model grid • in addition to parameterization of turbulent fluxes on the bases of an extended mosaic method, the mesoscale transport should be parameterized on the basis of • TS difference between ice and water • polynya width • wind component parallel to the polynya / ice edge.

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