ATMOSPHERIC HYDROLOGIC-CYCLE OVER THE SOUTHERN-OCEAN AND ANTARCTICA FROM OPERATIONAL NUMERICAL-ANALYSES

Moisture budget calculations for Antarctica and the Southern Ocean (40 degrees-72 degrees S) are performed using operational numerical analy ses from the European Centre for Medium-Range Weather Forecasts (ECMWF ), the National Meteorological Center (NMC), and the Australian Bureau of Meteorology (ABM). The analyses are intercompared for an 8-yr peri od from 1985 to 1992 and are evaluated against representative rawinson de sites, which are considered accurate depictions of moisture transpo rt at these sites. The comparisons to East Antarctic rawinsondes and t hose from Macquarie Island show the ECMWF analyses to be superior in r eproducing sounding values at each level. While results are highly var iable depending on the station location, agreement of the ECMWF analys es to zonally averaged sounding moisture Bur values along the East Ant arctic coast is very close. The zonally averaged annual meridional moi sture flux, for example, is within as little as 0.03 g kg(-1) m s(-1), or 2% at the surface. This is particularly good considering the highl y variable inflow and outflow patterns along the Antarctic perimeter. The NMC and ABM analyses generally underestimate transport at each lev el; error cancellation occurs during vertical integration however. A c omparison of moisture convergence for East Antarctica with values calc ulated from rawinsonde data indicates the ECMWF analysis is within 5 m m yr(-1) of the observed value, while the NMC result is severely defic ient. Overall these results are not surprising given the coarse resolu tion and spectral nature of the analyses. The ability of the ECMWF ana lyses to reproduce the observed moisture transport at each level is re assuring. Comparison of the moisture transport convergence derived fro m the numerical analyses with previous moisture flux studies over the Southern Ocean reveals general agreement in the location of the bounda ry between the moisture source and sink. The ECMWF and NMC analyses pl ace the convergence maximum slightly farther south than has been previ ously found. It is inferred that this results from the blocking effect of the Antarctic coastal topography. At full resolution this point is at approximately 64 degrees S. Long-term net precipitation (precipita tion minus sublimation/evaporation)derived from the numerical analyses is somewhat smaller than values determined by glaciological methods. Net precipitation varies interannually by 25%, with most of the variat ion concentrated in the South Pacific sector, the region of greatest p oleward moisture transport. The results presented here offer a substan tially more positive outlook on the prospects of determining continent al-scale precipitation trends in Antarctica through atmospheric method s than has been previously found and demonstrate that the ECMWF analys es provide generally good estimates.