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What makes high latitude fluxes different from more equatorward? Frequent high winds

What makes high latitude fluxes different from more equatorward? Frequent high winds Frequent large Δ T, Δ q. From Sampe and Xie, BAMS, Dec 2007. Observations at high winds.

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What makes high latitude fluxes different from more equatorward? Frequent high winds

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  1. What makes high latitude fluxes different from more equatorward? • Frequent high winds • Frequent large ΔT, Δq From Sampe and Xie, BAMS, Dec 2007

  2. Observations at high winds • Despite over 7000 hours of ID and Covariance fluxes in ETL database, only 133 & 85 hours are for U > 15 m/s (Fairall et al 2003) • So a lack of flux obs. under high winds is synonymous with lack of flux obs. at high latitudes.

  3. Low-level (30-50 m) flights from Greenland Flow Distortion experiment - Feb-Mar 2007 - Thicker lines = low-level

  4. Scatter at high winds is large Probably still not enough in situ observations at high windspeeds

  5. 2A) Are all flux parameterizations similar in their estimates of fluxes? - Below leg 6 from B276 flight on GFDex, over water.

  6. Fluxes over ice • Over MIZ and sea ice there appears to be even more scatter in covariance observations and even fewer observations available. • Below from GFDex; next few pages from recent Antarctic campaign

  7. Hot off the press… • February 2008 fieldwork by Emma Fiedler (UEA) in collaboration with BAS

  8. Coastal Polynya Aircraft Observations

  9. Results Decrease in sensible heat flux with fetch due to reduction in air-surface temperature difference – warming of the CIBL – surface temperature decrease

  10. Results Decrease in sensible heat flux with fetch due to reduction in air-surface temperature difference – warming of the CIBL – surface temperature decrease

  11. Transfer coefficients Consider only values from lower level legs due to the increased scatter at higher level Mean values same (flights 24hrs apart) CDN10 = 1.0 x 10-3 CHN10 = 6.8 x 10-4 Values are at lower end of previous observations No significant linear trend with fetch

  12. Is there a variation with surface characteristics? • Only the two lowest level legs were considered as the data is more reliable • There is no significant difference between the means of the coefficients for the two regimes (F54 to 30km, F57 to 55km) • As an indicator of surface ice type, the relationships between CD and CH with albedo and surface temperature were examined • No significant linear trends found (r2 values ~0.1) • Split into the two regimes, no clear distinction • At surface temperatures above ~-10 oC and albedos below ~0.4 there may be a linear relationship (but limited data)

  13. Fluxes over ice • Ice concentration, thickness and type possibly important for flux estimates • But hard to observe & model • Most models set 1 exchange coefficients for sea ice, and possibly 1 for MIZ.

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