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J. F. Le Marshall

Abstract

Fields of temperature, thickness and precipitable water, derived from common sets of Tiros Operational Vertical Sounder (TOVS) radiance data have been intercompared. These fields were produced by a variety of institutions using different retrieval techniques. The fields have been derived over three regions; the Alpine Experiment (ALPEX) in 1982, the Tasman Sea, and the United States. Basic statistics have been produced by comparing these derived fields to analyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF), and with collocated radiosonde (RAOB) data.

In most cases it appeared, for both physical and statistical retrieval techniques, that in the midtroposphere (700 to 400 mb) the satellite temperature soundings exhibited rms temperature differences of near 2 K when compared to ECMWF analysis or collocated radiosonde data. These figures include significant contributions due to radiosonde error, collocation differences, analysis error and other factors. Diferent vertical resolutions among the compared fields contributed to the larger differences which were evident near the tropopause and the surface. Near the surface the differences appeared to be more a function of the use of ancillary data or constraints, rather than the retrieval scheme. Basic statistics for thickness and moisture fields have also been presented in this study.

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John F. Le Marshall and Anthony J. Schreiner

Abstract

To date, operational satellite temperature retrieves from the TIROS-N/NOAA A–G series of satellites and a large percentage of those produced for research purposes have used statistical techniques to estimate limb effects in satellite-observed radiances. In this study, temperature profiles were derived using the radiative transfer equation in a form which properly takes into account the angle of observation. These temperature profiles were then compared to those derived using the radiative transfer equation with “nadir radiances” produced by a statistical limb correction technique similar to those now used operationally. This comparison revealed significant differences in the derived temperature profiles at large viewing angles, particularly in the case of strong meridional temperature gradients. Overall, the results suggest that for the calculation of temperature profiles from nonnadir observations, the more proper physical solution is the preferred procedure for deriving temperature fields.

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L. B. Guymer and J. F. Le Marshall

Surface pressure observations from the First GARP Global Experiment (FGGE) drifting buoys, transmitted over the Global Telecommunication System, have been used in the Melbourne National Meteorological Analysis Centre (NMAC) operational analysis program since December 1978. From the beginning of the first Special Observing Period the network of buoys was sufficient to provide a data base over many areas from which routine surface observations have never previously been available.

The great value of the new data in the specification of critical high latitude ridge axes, the true intensity of the Southern Ocean depressions and the westerly flow south of the Australian land mass is illustrated. It is shown that the 1979 analyses differ significantly from those of previous years, with regard to such features as the circumpolar trough, the middle latitude cyclonic systems and the sub-tropical highs. An appraisal of the differences indicates they are not only due to the characteristics of the 1979 circulation but also to a first delineation of the hemispheric circulation features by use of the FGGE data base.

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