VALIDATION OF OPERATIONAL NUMERICAL-ANALYSES IN ANTARCTIC LATITUDES

Available rawinsonde, automatic weather station (AWS), ship, and synth esized long-term observations are used to evaluate the Antarctic numer ical analyses of the European Centre for Medium-Range Weather Forecast s (ECMWF) and the U.S. National Centers for Environmental Prediction ( NCEP) from 1985 to 1994. Twice-daily variations in the ECMWF surface p ressure analyses compare closely with AWS units of the U.S. Antarctic Program and ship observations. The NCEP analyses lover the same period show substantial improvement, particularly during the period 1985-199 0. Surface air temperatures and winds do not agree so closely, which m ay result from analyses error, the localized nature of the fields, or a combination. Validation of the analyses standard pressure level fiel ds using available rawinsonde data reveal a general long-term decrease in RMS errors with time for both analyses. RMS errors in NCEP 200 hPa geopotential heights of over 200 geopotential meters (gpm) for centra l plateau stations are evident only prior to May 1986. However, a sign ificant upward trend from 1989 to 1993 in geopotential height RMS diff erences is apparent at several levels. The ECMWF analyses are generall y found to be superior and offer a reasonable depiction of the broadsc ale atmospheric circulation; however, deficiencies in midtropospheric temperatures and lower tropospheric winds are evident. Comparisons of ship data from individual cruises of the S.A. Agulhas and the RN Natha niel B. Palmer to the numerical analyses reveal substantial agreement for pressure and temperature variables. Observations from the Nathanie l B. Palmer in the Amundsen and Bellingshausen Seas were not available to the weather forecasting centers. Results presented here indicate t hat a large amount of the available data is being incorporated and tha t large deficiencies identified in previous studies are being addresse d, although areas of concern remain. Deficiencies in comparisons to sp ecific stations are common to both analyses, implying continued commun ications problems. In particular, grid values corresponding to individ ual stations including the now-closed Leningradskaya base and Mirnyy a re found to be conspicuously deficient at the 200 hPa level for both a nalyses.