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Stephen F. Pendlebury
,
Neil D. Adams
,
Terry L. Hart
, and
John Turner

Abstract

Increasingly, output from numerical weather prediction (NWP) models is being used for real-time weather forecasts for the Antarctic and for Antarctic-related climate diagnostics studies. Evidence is presented that indicates that in broad terms, the NWP output from the major global models is providing useful representations of synoptic-scale systems over high southern latitude areas. For example, root-mean-square (rms) errors in the European Centre for Medium-Range Weather Forecasts (ECMWF) model predictions of the 500-hPa height field indicate a day's gain in predictability since the mid-1990s: average rms errors in ECMWF +72 h 500-hPa height field prognoses for the calendar year 2000 were close to 50 m, compared to similar errors in the +48 h prognoses in 1995. Similar relative improvements may be noted for all time steps out to +144 h. Moreover, it is determined that, of the models considered here, the ECMWF model is clearly the most successful model at 500-hPa-height prediction for high southern latitudes, with the United Kingdom Met Office (UKMO) and National Centers for Environmental Prediction Aviation (AVN) models the next most accurate, and with the Australian Bureau of Meteorology's Global Assimilation Prediction (GASP) and Japanese Meteorological Agency (JMA) models lagging in accuracy. However, improvements in the temporal and spatial resolution of observational data that are available to the analysis and assimilation cycles of the NWP models, and improvements in the horizontal resolutions of the models, are required before the use of NWP output at high southern latitudes is as effective as in more northern areas of the world. Limited area modeling is seen as having potential for complementing the global models by resolving the finer-scale orography and topography of the Antarctic.

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John Turner
,
Steven Leonard
,
Gareth J. Marshall
,
Michael Pook
,
Lance Cowled
,
Richard Jardine
,
Stephen Pendlebury
, and
Neil Adams

Abstract

The quality of the Antarctic operational analyses that were distributed over the Global Telecommunications System during the First Regional Observing Study of the Troposphere project special observing period of July 1994 is considered. Numerical analyses from the U.K. Meteorological Office, the European Centre for Medium-Range Weather Forecasts, the Australian Bureau of Meteorology, and the U.S. National Centers for Environmental Prediction are compared with high quality analyses prepared using all available late data and high-resolution satellite imagery. The subjective assessment of the analyses indicated that no large, synoptic-scale systems were missing, but major discrepancies were found in terms of the depth of the lows, location errors, and failures to resolve the complexities of systems. Generally, the central pressures of the lows were handled better than the locations of the centers. Only 4 lows out of a total of 161 in the Eastern Hemisphere during the period 22–28 July had to be relocated more than 500 km. High-quality satellite imagery was very important in correcting the locations of the lows and in resolving the structure of multicentered systems, which were often found to be much more complex than analyzed on the operational charts. The satellite imagery was of less value over the continent since some of the lows here, which were analyzed using automatic weather station data, had no cloud associated with them as a result of the atmosphere being very dry. Few changes were made to the positions of anticyclones and only minor modifications to ridges were required. The mean pressure at mean sea level fields for July 1994 as produced by the four models were all very similar, but the Australian model stood out as slightly different over the Amundsen Sea because of large differences in the handling on one large low during the early part of the month. The Phillpot technique for the analysis of the 500-hPa surface over the interior of the continent was of particular value in resolving structure in the circulation.

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