What makes high latitude fluxes different from more equatorward?

• Frequent high winds• Frequent large ΔT, Δq

From Sampe and Xie,BAMS, Dec 2007

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.

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

Scatter at high winds is largeProbably still not enough in situ observations at high windspeeds

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

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

Hot off the press…

• February 2008 fieldwork by Emma Fiedler (UEA) in collaboration with BAS

Coastal Polynya Aircraft Observations

ResultsResultsDecrease in sensible heat flux Decrease in sensible heat flux with fetch due to reduction in air-with fetch due to reduction in air-surface temperature differencesurface temperature difference

– – warming of the CIBLwarming of the CIBL

– – surface temperature decreasesurface temperature decrease

ResultsResultsDecrease in sensible heat flux Decrease in sensible heat flux with fetch due to reduction in air-with fetch due to reduction in air-surface temperature differencesurface temperature difference

– – warming of the CIBLwarming of the CIBL

– – surface temperature decreasesurface temperature decrease

Consider only values Consider only values from lower level legs from lower level legs due to the increased due to the increased scatter at higher levelscatter at higher level

Mean values same Mean values same (flights 24hrs apart)(flights 24hrs apart)

CCDN10DN10 = 1.0 x 10 = 1.0 x 10-3-3

CCHN10HN10 = 6.8 x 10 = 6.8 x 10-4-4

Values are at lower end Values are at lower end of previous of previous observations observations

No significant linear No significant linear trend with fetchtrend with fetch

Transfer coefficients

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)

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.