HR: 15:00h
AN: A23E-05    [Abstracts]
TI: Sampling errors in VOS-based surface air-sea fluxes: estimation, impacts and minimization.
AU: * Gulev, S
EM: gul@sail.msk.ru
AF: Sergey Gulev, IORAS, 36 Nakhimovsky ave., Moscow, 117997, Russian Federation
AB: Sampling uncertainties in the voluntary observing ship (VOS)-based global ocean-atmosphere flux fields were estimated using different NWP flux products and the procedure of subsampling, simulating VOS-like sampling density in NWP flux products. The highest random sampling errors in surface fluxes were found for the sensible and latent heat flux and range from 30 to 80 Wm-2. Total sampling errors in poorly sampled areas may be higher than random ones by 60%. In poorly sampled subpolar latitudes of the Northern Hemisphere and throughout much of the Southern Ocean the total sampling uncertainty in the net heat flux can amount to 80-100 Wm-2. The largest uncertainties in linear trend estimates are found in the high-latitude North Atlantic and North Pacific as well as the Southern Ocean, where trends can locally show opposite signs when computed from the regularly sampled and undersampled data. Spatial patterns of shorter-period interannual variability, quantified through the EOF analysis, also show remarkable differences between the regularly sampled and undersampled flux datasets in the Labrador Sea and northwest Pacific. In order to minimize sampling errors in VOS fluxes we suggested a methodology of climatological averaging of fluxes based on the application of double-exponential distributions (2ePDF) of sensible and latent surface flux estimates. Application of 2ePDF allows for minimization of sampling errors from 2 to 10 times and provides much more reliable global surface turbulent flux fields. Then, using the same methodology and 125 years (1880-2004) of VOS observations from ICOADS we reconstruct surface ocean- atmosphere heat fluxes over the North Atlantic with monthly resolution in time and variable (2-degree to 5-degree) resolution in space. Produced air-sea flux fields show reasonable minimization of sampling errors and allow for the analysis of regional heat balances and estimation of long-term changes in surface fluxes. Further analysis included computation of monthly anomalies of surface fluxes as well as estimation of the subpolar gyre heat and freshwater budgets. These were computed using two-demensional distributions of surface fluxes in the coordinates of sea-air temperature difference and wind speed. Reconstructed fluxes reveal long-term trends, implying, for example, about 4 W/m2 per decade growing sensible heat fluxes in the Labrador Sea and about 2 W/m2 per decade secular increase in the Central subpolar gyre. Non-secular signals are represented by the decadal-scale and multidecadal (about 40-50 years variability). Decadal scale signal has a clear association with the NAO-like atmospheric circulation variability during 1880-1915 and after 1955, but has a little association with NAO between 1915 and 1955.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4504 Air/sea interactions (0312, 3339)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly