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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.
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.
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.
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.
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.
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.
The International Winds Workshops interact with the Co-ordination Group for Meteorological Satellites with respect to important issues related to the derivation and utilization of wind information based on the imagery from geostationary satellites. It also provides a forum for data producers, data users, and the science community to exchange information on the characteristics of satellite-tracked winds and to optimize their use in several applications, including numerical weather prediction, nowcasting, and climate applications. The sequence of meetings began in Washington, D.C., in September 1991. Since then, meetings have been held in Tokyo, Japan, in December 1993; Ascona, Switzerland, in June 1996; and in Saanenmoser, Switzerland, in October 1998. This report describes the proceedings at the Fifth International Winds Workshop and includes the recommendations derived from the meeting.
The International Winds Workshops interact with the Co-ordination Group for Meteorological Satellites with respect to important issues related to the derivation and utilization of wind information based on the imagery from geostationary satellites. It also provides a forum for data producers, data users, and the science community to exchange information on the characteristics of satellite-tracked winds and to optimize their use in several applications, including numerical weather prediction, nowcasting, and climate applications. The sequence of meetings began in Washington, D.C., in September 1991. Since then, meetings have been held in Tokyo, Japan, in December 1993; Ascona, Switzerland, in June 1996; and in Saanenmoser, Switzerland, in October 1998. This report describes the proceedings at the Fifth International Winds Workshop and includes the recommendations derived from the meeting.
Abstract
A data assimilation scheme for the Southern Hemisphere has been incorporated into the ANMRC hemi-insertion frequency of six hours and has been performed with the FGGE data base for the period 17–26 and the model has been designed to accept data at any or all time steps. After each analysis a nonlinear normal mode initialization is performed. The initial evaluation of the analysis scheme has used a data insertion frequency of six hours and has been performed with the FGGE data base for the period 17–26 May 1979. Comparison with Australian Bureau of Meteorology operational analyses is presented, together with diagnostic evaluation of detailed aspects of the assimilation scheme.
Abstract
A data assimilation scheme for the Southern Hemisphere has been incorporated into the ANMRC hemi-insertion frequency of six hours and has been performed with the FGGE data base for the period 17–26 and the model has been designed to accept data at any or all time steps. After each analysis a nonlinear normal mode initialization is performed. The initial evaluation of the analysis scheme has used a data insertion frequency of six hours and has been performed with the FGGE data base for the period 17–26 May 1979. Comparison with Australian Bureau of Meteorology operational analyses is presented, together with diagnostic evaluation of detailed aspects of the assimilation scheme.
AIRS
Improving Weather Forecasting and Providing New Data on Greenhouse Gases
The Atmospheric Infrared Sounder (AIRS) and its two companion microwave sounders, AMSU and HSB were launched into polar orbit onboard the NASA Aqua Satellite in May 2002. NASA required the sounding system to provide high-quality research data for climate studies and to meet NOAA's requirements for improving operational weather forecasting. The NOAA requirement translated into global retrieval of temperature and humidity profiles with accuracies approaching those of radiosondes. AIRS also provides new measurements of several greenhouse gases, such as CO2, CO, CH4, O3, SO2, and aerosols.
The assimilation of AIRS data into operational weather forecasting has already demonstrated significant improvements in global forecast skill. At NOAA/NCEP, the improvement in the forecast skill achieved at 6 days is equivalent to gaining an extension of forecast capability of six hours. This improvement is quite significant when compared to other forecast improvements over the last decade. In addition to NCEP, ECMWF and the Met Office have also reported positive forecast impacts due AIRS.
AIRS is a hyperspectral sounder with 2,378 infrared channels between 3.7 and 15.4 μm. NOAA/NESDIS routinely distributes AIRS data within 3 hours to NWP centers around the world. The AIRS design represents a breakthrough in infrared space instrumentation with measurement stability and accuracies far surpassing any current research or operational sounder..The results we describe in this paper are “work in progress,” and although significant accomplishments have already been made much more work remains in order to realize the full potential of this suite of instruments.
The Atmospheric Infrared Sounder (AIRS) and its two companion microwave sounders, AMSU and HSB were launched into polar orbit onboard the NASA Aqua Satellite in May 2002. NASA required the sounding system to provide high-quality research data for climate studies and to meet NOAA's requirements for improving operational weather forecasting. The NOAA requirement translated into global retrieval of temperature and humidity profiles with accuracies approaching those of radiosondes. AIRS also provides new measurements of several greenhouse gases, such as CO2, CO, CH4, O3, SO2, and aerosols.
The assimilation of AIRS data into operational weather forecasting has already demonstrated significant improvements in global forecast skill. At NOAA/NCEP, the improvement in the forecast skill achieved at 6 days is equivalent to gaining an extension of forecast capability of six hours. This improvement is quite significant when compared to other forecast improvements over the last decade. In addition to NCEP, ECMWF and the Met Office have also reported positive forecast impacts due AIRS.
AIRS is a hyperspectral sounder with 2,378 infrared channels between 3.7 and 15.4 μm. NOAA/NESDIS routinely distributes AIRS data within 3 hours to NWP centers around the world. The AIRS design represents a breakthrough in infrared space instrumentation with measurement stability and accuracies far surpassing any current research or operational sounder..The results we describe in this paper are “work in progress,” and although significant accomplishments have already been made much more work remains in order to realize the full potential of this suite of instruments.
