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Terry L. Hart, William Bourke, Bryant J. McAvaney, Bruce W. Forgan, and John L. McGregor

Abstract

Results are presented for perpetual January and July general circulation simulations using the Australian Bureau of Meteorology Research Centre global spectral model. Particular emphasis is placed on the impact of changes in the physical parameterizations and horizontal resolution on the modeled fields. The results include variances and eddy transports as well as zonal means and geographical distributions. Of the experiments conducted the most satisfactory results were obtained using stability-dependent vertical diffusion and a combination of the Kuo scheme for deep convection and the Tiedtke shallow convection scheme.

The simulation of the polar night region of the stratosphere in January was much more realistic than in results obtained using an earlier version of the model. The improvement is attributed to the revised radiation code, supporting the conclusions of Ramanathan et al. on the sensitivity of simulations of this region of the atmosphere to the treatment of radiative processes.

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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, David Bromwich, Steven Colwell, Stephen Dixon, Tim Gibson, Terry Hart, Günther Heinemann, Hugh Hutchinson, Kieran Jacka, Steven Leonard, Michael Lieder, Lawrie Marsh, Stephen Pendlebury, Henry Phillpot, Mike Pook, and Ian Simmonds

An account is given of the Antarctic First Regional Observing Study of the Troposphere (FROST) project, which has been organized by the Physics and Chemistry of the Atmosphere Group of the Scientific Committee on Antarctic Research. The goals of FROST are to study the meteorology of the Antarctic, to determine the strengths and weaknesses of operational analyses and forecasts over the continent and in the surrounding ocean areas, and to assess the value of new forms of satellite data that are becoming available. FROST is based around three one-month Special Observing Periods (SOPs)—July 1994, 16 October–15 November 1994, and January 1995 for which comprehensive datasets have been established of model fields and in situ and satellite observations. High quality manual surface and upper-air analyses are being prepared for these periods to determine the extent to which non–Global Telecommunications System data can improve the interpretation of the synoptic situation. Over the ocean areas during SOP-1, incorporation of the late data resulted only in a limited improvement in the analyses, indicating that the models are correctly analyzing most of the major weather systems. Over the continent, the production of 500-hPa heights from the automatic weather station data greatly helped in the analysis process. The lack of data around west Antarctica was a major handicap in the analysis process. The rms errors in the forecasts of 500-hPa height for the Antarctic were about 20% greater than those for midlatitude areas. The forecasts from the European Centre for Medium-Range Weather Forecasts were the most accurate of those received.

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