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Abstract
Vertical soundings of temperature and moisture derived from the GOES VISSR Atmospheric Sounder (VAS) measurements have been produced operationally since summer 1987 at the VAS Data Utilization Center (VDUC). The algorithm which was developed for the VDUC is described here in detail. Tunable features are identified, and their sensitivities are shown. The algorithm is used to process a case study for 6 March 1982 to examine its capability in a rapidly evolving weather pattern. Weaknesses are exposed, in particular the bias errors in the retrievals and the dependence on first guesses, but strengths are also evident, namely, the capacity to refine gradients and patterns in a manner which improves the first guesses.
Abstract
Vertical soundings of temperature and moisture derived from the GOES VISSR Atmospheric Sounder (VAS) measurements have been produced operationally since summer 1987 at the VAS Data Utilization Center (VDUC). The algorithm which was developed for the VDUC is described here in detail. Tunable features are identified, and their sensitivities are shown. The algorithm is used to process a case study for 6 March 1982 to examine its capability in a rapidly evolving weather pattern. Weaknesses are exposed, in particular the bias errors in the retrievals and the dependence on first guesses, but strengths are also evident, namely, the capacity to refine gradients and patterns in a manner which improves the first guesses.
Abstract
Temperature data derived from Nimbus 4 SIRS radiance measurements have been used in four-dimensional assimilation experiments with a simple two-level primitive equation model. Data are inserted into a running forecast on an orbit-by-orbit basis. The method of insertion is held fixed but initial conditions and techniques for achieving geostrophic adjustment are varied. It is shown that the real temperature data can be readily assimilated and retained by the model, and that the assimilation is greatly enhanced if a simple wind law initialization is performed at the time of insertion. There is a suggestion that four-dimensional assimilation is a viable operational procedure and a somewhat milder suggestion that it is a more effective way of utilizing asynoptic data than updating procedures currently in practice.
Abstract
Temperature data derived from Nimbus 4 SIRS radiance measurements have been used in four-dimensional assimilation experiments with a simple two-level primitive equation model. Data are inserted into a running forecast on an orbit-by-orbit basis. The method of insertion is held fixed but initial conditions and techniques for achieving geostrophic adjustment are varied. It is shown that the real temperature data can be readily assimilated and retained by the model, and that the assimilation is greatly enhanced if a simple wind law initialization is performed at the time of insertion. There is a suggestion that four-dimensional assimilation is a viable operational procedure and a somewhat milder suggestion that it is a more effective way of utilizing asynoptic data than updating procedures currently in practice.
Abstract
Standard atmospheric energy budget computations are made for three distinct sets of Northern Hemisphere synoptic analyses prepared from data gathered during the August 1975 Data Systems Test. The first analysis set (System 1) included all data, the second (System 2) all but the satellite temperature retrievals (excepting some retained in the Southern Hemisphere for analysis model stability), and the third (System 3) all but the rawinsondes. Our results indicate that significant differences occur in the energetics of the analyses. In particular, there is a significant loss of longitudinal variance in an analysis based mainly on satellite retrievals as compared to that based mainly on rawinsonde data. In addition, forecasts by the NMC 6-layer numerical model initiated from System 1 and 2 analyses were evaluated for forecast periods from 00 to 72 h. It appears that this forecast model is sensitive to variations supplied by the initial data sets, but only to 12 h. Thereafter the forecast energetics are controlled by the model physics, and energy differences evolving from the different data sets remain constant in time.
Abstract
Standard atmospheric energy budget computations are made for three distinct sets of Northern Hemisphere synoptic analyses prepared from data gathered during the August 1975 Data Systems Test. The first analysis set (System 1) included all data, the second (System 2) all but the satellite temperature retrievals (excepting some retained in the Southern Hemisphere for analysis model stability), and the third (System 3) all but the rawinsondes. Our results indicate that significant differences occur in the energetics of the analyses. In particular, there is a significant loss of longitudinal variance in an analysis based mainly on satellite retrievals as compared to that based mainly on rawinsonde data. In addition, forecasts by the NMC 6-layer numerical model initiated from System 1 and 2 analyses were evaluated for forecast periods from 00 to 72 h. It appears that this forecast model is sensitive to variations supplied by the initial data sets, but only to 12 h. Thereafter the forecast energetics are controlled by the model physics, and energy differences evolving from the different data sets remain constant in time.
One aspect of the modernized observational capability of the National Weather Service will be geostationary sounding of temperature and moisture from GOES-I, currently scheduled for launch in 1992. The capability has evolved from ten years of research with the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS). This article summarizes that evolution and describes the initial operational sounder products expected of GOESI. The effect on products caused by problems in meeting performance specifications are discussed. The outlook for follow-on sounders in the next series (circa 2000) of GOES is also briefly treated.
One aspect of the modernized observational capability of the National Weather Service will be geostationary sounding of temperature and moisture from GOES-I, currently scheduled for launch in 1992. The capability has evolved from ten years of research with the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS). This article summarizes that evolution and describes the initial operational sounder products expected of GOESI. The effect on products caused by problems in meeting performance specifications are discussed. The outlook for follow-on sounders in the next series (circa 2000) of GOES is also briefly treated.
Abstract
A recursive filter objective analysis method is described. It is a "successive approximation" system with the particular feature of locally varying scaling, making it especially appropriate for dealing with inhomogeneous data. Attention is given to proper treatment of lateral boundaries, which permit its use in limited domains. Thissystem provides estimates of input data quality that can be used for editing datasets before their distribution and for the weighting of data in application by other users, Two- and three-dimensional versions of the analysis operating on a Cartesian grid are used operationally at the National Environmental Satellite and Data InformationService. They are used both in the production of data and for quality control prior to dissemination. Examplesof these applications are given.
Abstract
A recursive filter objective analysis method is described. It is a "successive approximation" system with the particular feature of locally varying scaling, making it especially appropriate for dealing with inhomogeneous data. Attention is given to proper treatment of lateral boundaries, which permit its use in limited domains. Thissystem provides estimates of input data quality that can be used for editing datasets before their distribution and for the weighting of data in application by other users, Two- and three-dimensional versions of the analysis operating on a Cartesian grid are used operationally at the National Environmental Satellite and Data InformationService. They are used both in the production of data and for quality control prior to dissemination. Examplesof these applications are given.
Abstract
This note describes the assimilation of sub-synoptic resolution satellite-derived temperature and moisture profiles into a mesoscale numerical weather prediction model, intended for forecasting the environment of organized convective storm complexes in the midwest of the United States. It is demonstrated that the use of high resolution satellite data to initialize this system results in a good level of forecast accuracy for the case study chosen, with very encouraging accuracy in the forecast moisture and vertical motion fields. It is also demonstrated that it is not simply the satellite data, but also the high horizontal resolution of these data, which positively affect the accuracy of the satellite data forecast.
Abstract
This note describes the assimilation of sub-synoptic resolution satellite-derived temperature and moisture profiles into a mesoscale numerical weather prediction model, intended for forecasting the environment of organized convective storm complexes in the midwest of the United States. It is demonstrated that the use of high resolution satellite data to initialize this system results in a good level of forecast accuracy for the case study chosen, with very encouraging accuracy in the forecast moisture and vertical motion fields. It is also demonstrated that it is not simply the satellite data, but also the high horizontal resolution of these data, which positively affect the accuracy of the satellite data forecast.
Abstract
The retrieval of temperature from satellite-observed radiances has traditionally been addressed as a one-dimensional or columnar problem which uses a guess profile of temperature. In this study, the traditional approach is augmented by incorporating observed wind shear as a general thermal wind constraint in the inversion of radiances to make a three-dimensional temperature analysis.
The problem is cast as a classical variational problem that minimizes a weighted sum of squares subject to constraint. The constraints are the general thermal wind equation and a set of regression equations expressing the radiances in terms of the temperature profile. The solution is found by the method of conjugate gradients.
Experiments using observed winds with both simulated and observed radiances for the GOES VISSR Atmospheric Sounder (VAS) are described. In both cases, a first guess from a numerical forecast is used. Simulated radiances are used to establish the optimal relative weighting of the wind versus radiance observations and to determine the limits of accuracy on the retrieved temperature under idealized conditions. These relative weights are used in the real data experiments. Experiments are included where weights are varied horizontally and vertically to simulate uneven distribution or confidence in the data. Results indicate that (i) the inclusion of wind shear with simulated radiances reduces the cumulative error variance in the temperature estimate and reduces guess dependence; (ii) horizontal and vertical variations in parameter weighting is viable and well-behaved; and (iii) the algorithm's rate of convergence makes it suitable for small computer applications.
Experiments with observed radiances are not as successful. The measured radiances do not improve the forecast. The principal deficiency appears to be that the regression model for expressing the radiances is inadequate to account for the influence of water vapor which affect the VAS measurements or the nonlinearity of radiance with respect to temperature. Extensions to the model as well as application to microwave measurements, which do not suffer these deficiencies, are discussed.
Abstract
The retrieval of temperature from satellite-observed radiances has traditionally been addressed as a one-dimensional or columnar problem which uses a guess profile of temperature. In this study, the traditional approach is augmented by incorporating observed wind shear as a general thermal wind constraint in the inversion of radiances to make a three-dimensional temperature analysis.
The problem is cast as a classical variational problem that minimizes a weighted sum of squares subject to constraint. The constraints are the general thermal wind equation and a set of regression equations expressing the radiances in terms of the temperature profile. The solution is found by the method of conjugate gradients.
Experiments using observed winds with both simulated and observed radiances for the GOES VISSR Atmospheric Sounder (VAS) are described. In both cases, a first guess from a numerical forecast is used. Simulated radiances are used to establish the optimal relative weighting of the wind versus radiance observations and to determine the limits of accuracy on the retrieved temperature under idealized conditions. These relative weights are used in the real data experiments. Experiments are included where weights are varied horizontally and vertically to simulate uneven distribution or confidence in the data. Results indicate that (i) the inclusion of wind shear with simulated radiances reduces the cumulative error variance in the temperature estimate and reduces guess dependence; (ii) horizontal and vertical variations in parameter weighting is viable and well-behaved; and (iii) the algorithm's rate of convergence makes it suitable for small computer applications.
Experiments with observed radiances are not as successful. The measured radiances do not improve the forecast. The principal deficiency appears to be that the regression model for expressing the radiances is inadequate to account for the influence of water vapor which affect the VAS measurements or the nonlinearity of radiance with respect to temperature. Extensions to the model as well as application to microwave measurements, which do not suffer these deficiencies, are discussed.
Abstract
Derived product imagery (DPI) is a method of presenting quantitative meteorological information, derived from satellite measurements, as a color-coded image at single-pixel resolution. Its intended use is as animated sequences to observe trends in the displayed quantities, which for the GOES-8 are total precipitable water, lifted index, and surface skin temperature. Those products are produced once per hour, over the continental United States and the Gulf of Mexico. This paper reviews the development of the DPI and details the algorithm used for GOES-8. The quality of the products is discussed, and an example is given. The greatest value of the DPI probably lies in comparing a sequence of the satellite product with a sequence derived from a numerical forecast. In this way, deviation of the forecast from reality is readily exposed.
Abstract
Derived product imagery (DPI) is a method of presenting quantitative meteorological information, derived from satellite measurements, as a color-coded image at single-pixel resolution. Its intended use is as animated sequences to observe trends in the displayed quantities, which for the GOES-8 are total precipitable water, lifted index, and surface skin temperature. Those products are produced once per hour, over the continental United States and the Gulf of Mexico. This paper reviews the development of the DPI and details the algorithm used for GOES-8. The quality of the products is discussed, and an example is given. The greatest value of the DPI probably lies in comparing a sequence of the satellite product with a sequence derived from a numerical forecast. In this way, deviation of the forecast from reality is readily exposed.
Abstract
Visible-Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) moisture retrievals are compared to the National Meteorological Center Regional Analysis and Forecast System (RAFS) 12-h forecast and to 1200 UTC rawinsondes over the United States and the Gulf of Mexico on a daily basis for nearly 1.5 years. The principal objective is to determine what information the current moisture retrieval add to that available from the RAFS and surface data. The data are examined from the climatological perspective, that is, total precipitable water over the seasons for three geographical regions, and also for synoptic applications, that is, vertical and horizontal resolution. VAS retrievals are found to be systematically too moist at higher values. The variance of the VAS soundings more closely agrees with the rawinsonde at locations around the Gulf of Mexico than the RAFS. An examination of a case (6 June 1989) over the Gulf of Mexico region comparing three layers of VAS-derived moisture to the RAFS forecast shows the former capable of outperforming the latter in both the horizontal and, to some extent, the vertical frame of reference.
Abstract
Visible-Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) moisture retrievals are compared to the National Meteorological Center Regional Analysis and Forecast System (RAFS) 12-h forecast and to 1200 UTC rawinsondes over the United States and the Gulf of Mexico on a daily basis for nearly 1.5 years. The principal objective is to determine what information the current moisture retrieval add to that available from the RAFS and surface data. The data are examined from the climatological perspective, that is, total precipitable water over the seasons for three geographical regions, and also for synoptic applications, that is, vertical and horizontal resolution. VAS retrievals are found to be systematically too moist at higher values. The variance of the VAS soundings more closely agrees with the rawinsonde at locations around the Gulf of Mexico than the RAFS. An examination of a case (6 June 1989) over the Gulf of Mexico region comparing three layers of VAS-derived moisture to the RAFS forecast shows the former capable of outperforming the latter in both the horizontal and, to some extent, the vertical frame of reference.
Abstract
A method is presented for deducing lower troposphere moisture fields from radiances measured by the operational polar orbiting NOAA satellites. Statistical evaluation of the technique demonstrates the viability of the approach. A case study with TIROS-N observations shows substantial improvement over current operational methods, and a qualitatively reasonable product. High moisture gradients are clearly defined and horizontal consistency is achieved. The technique appears useful for the initialization of subsynoptic forecast models.
Abstract
A method is presented for deducing lower troposphere moisture fields from radiances measured by the operational polar orbiting NOAA satellites. Statistical evaluation of the technique demonstrates the viability of the approach. A case study with TIROS-N observations shows substantial improvement over current operational methods, and a qualitatively reasonable product. High moisture gradients are clearly defined and horizontal consistency is achieved. The technique appears useful for the initialization of subsynoptic forecast models.
