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- Author or Editor: Ralph A. Petersen x
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Abstract
Recent developments in meteorological objective analysis have been directed towards improving numerical model initialization, often at the expense of preserving detail in data rich regions. The objective scheme presented here is designed to give detailed, yet computationally efficient analyses over data rich regions and to be independent of any numerical model influences. The results, which accurately preserve observed data and gradient information, are particularly suited to diagnostic studies. The analysis scheme uses both observed station data and interstation gradients to interpolate pressure, wind, and moisture information from vertical cross sections onto isentropic surfaces using cubic polynomials. Three-dimensional grid point mass and moisture analyses at specified isentropic intervals are obtained by first constructing a series of nearly parallel, north–south vertical cross sections over an area of interest and then filling in the space between adjacent vertical analyses using a second set of nearly orthogonal cross sections. The choice of isentropic coordinates allows the objective analysis to use detailed information included within the vertical structure of sets of individual, quality-controlled soundings to capture significant horizontal thermal gradients. Gradients obtained from the mass analyses are then combined with observed wind data to obtain observed wind analyses which have spatial variations consistent with the scales of variations noted in the detailed mass fields. Examples are given which illustrate the detail and continuity inherent in the technique when applied to radiosonde data obtained at a variety of scales.
Abstract
Recent developments in meteorological objective analysis have been directed towards improving numerical model initialization, often at the expense of preserving detail in data rich regions. The objective scheme presented here is designed to give detailed, yet computationally efficient analyses over data rich regions and to be independent of any numerical model influences. The results, which accurately preserve observed data and gradient information, are particularly suited to diagnostic studies. The analysis scheme uses both observed station data and interstation gradients to interpolate pressure, wind, and moisture information from vertical cross sections onto isentropic surfaces using cubic polynomials. Three-dimensional grid point mass and moisture analyses at specified isentropic intervals are obtained by first constructing a series of nearly parallel, north–south vertical cross sections over an area of interest and then filling in the space between adjacent vertical analyses using a second set of nearly orthogonal cross sections. The choice of isentropic coordinates allows the objective analysis to use detailed information included within the vertical structure of sets of individual, quality-controlled soundings to capture significant horizontal thermal gradients. Gradients obtained from the mass analyses are then combined with observed wind data to obtain observed wind analyses which have spatial variations consistent with the scales of variations noted in the detailed mass fields. Examples are given which illustrate the detail and continuity inherent in the technique when applied to radiosonde data obtained at a variety of scales.
Abstract
Several different forms of lifted index (LI) calculations are available from the Limited-Area Fine Mesh Model (LFM) and Nested-Grid Model (NGM) run operationally at the National Meteorological Center (NMC). The differences between the index calculations are presented, various applications of the LI are discussed, and a case demonstrating some of the strengths and weaknesses of each is presented.
Abstract
Several different forms of lifted index (LI) calculations are available from the Limited-Area Fine Mesh Model (LFM) and Nested-Grid Model (NGM) run operationally at the National Meteorological Center (NMC). The differences between the index calculations are presented, various applications of the LI are discussed, and a case demonstrating some of the strengths and weaknesses of each is presented.
Abstract
An explicit technique for computing atmospheric trajectories, based on Greenspan's discrete model formulation, is presented as an alternative to the commonly used implicit scheme. The method provides an economical means of objectively obtaining computer-generated trajectories and accounts for the variable accelerations and local ψtendencies along the entire trajectory path. The initial results presented show that the explicit computations are stable and very nearly energy-conservative. An application of the discrete model approach to a real data base and comparisons with trajectories determined by the implicit method yield favorable results, illustrating the utility of the explicit technique as a diagnostic tool.
Abstract
An explicit technique for computing atmospheric trajectories, based on Greenspan's discrete model formulation, is presented as an alternative to the commonly used implicit scheme. The method provides an economical means of objectively obtaining computer-generated trajectories and accounts for the variable accelerations and local ψtendencies along the entire trajectory path. The initial results presented show that the explicit computations are stable and very nearly energy-conservative. An application of the discrete model approach to a real data base and comparisons with trajectories determined by the implicit method yield favorable results, illustrating the utility of the explicit technique as a diagnostic tool.
Abstract
Overlapping second-order Lagrangian polynomials are used to construct cross-sectional isentropic analyses from upper air sounding observations. Estimates of geostrophic winds are obtained through the thermal wind relationship. Thermal information is also combined with normal components of the observed wind to obtain a thermally enhanced, observed wind analysis. Results using these techniques are presented and compared with a previous objective analysis technique developed by Shapiro and Hastings (1973). Examination of the results indicates the applicability of the techniques both for operational and research purposes.
Abstract
Overlapping second-order Lagrangian polynomials are used to construct cross-sectional isentropic analyses from upper air sounding observations. Estimates of geostrophic winds are obtained through the thermal wind relationship. Thermal information is also combined with normal components of the observed wind to obtain a thermally enhanced, observed wind analysis. Results using these techniques are presented and compared with a previous objective analysis technique developed by Shapiro and Hastings (1973). Examination of the results indicates the applicability of the techniques both for operational and research purposes.
Abstract
An overview of the regularly scheduled sequence of computer analyses and forecasts produced at the National Meteorological Center (NMC) is presented. The available computer resources and time schedule constraints are discussed, the sources and treatment of incoming data are described, the purposes and configurations of the operational analysis/forecasting systems are outlined, and the mechanisms for product distribution are presented.
Abstract
An overview of the regularly scheduled sequence of computer analyses and forecasts produced at the National Meteorological Center (NMC) is presented. The available computer resources and time schedule constraints are discussed, the sources and treatment of incoming data are described, the purposes and configurations of the operational analysis/forecasting systems are outlined, and the mechanisms for product distribution are presented.
Abstract
The response of the Regional Analysis and Forecast System (RAFS) low-level forecast fields to the geographical distribution of snow cover is discussed. The errors produced by an improper specification of this field in the forecast model can have a wide variety of local forecasting implications, ranging from poor forecasts of lee-side Great Lakes snowfalls, to errors in forecasts of the earth's surface temperature in areas where the snow cover is changing rapidly. The use of the snow-cover data in the forecast model and its effect on forecast guidance are described.
Abstract
The response of the Regional Analysis and Forecast System (RAFS) low-level forecast fields to the geographical distribution of snow cover is discussed. The errors produced by an improper specification of this field in the forecast model can have a wide variety of local forecasting implications, ranging from poor forecasts of lee-side Great Lakes snowfalls, to errors in forecasts of the earth's surface temperature in areas where the snow cover is changing rapidly. The use of the snow-cover data in the forecast model and its effect on forecast guidance are described.
Abstract
The recent advancement of mini- and microcomputers into the local-work environment can provide local forecast offices with the capability to run simple numerical models for specific nowcasting and short-term forecast needs. While the capabilities of sophisticated, centralized modeling systems continue to progress, short-term forecasts are hampered by a number of inadequacies in this guidance, ranging from numerical deficiencies of the models to the inability to access the gridded model output in a timely manner and view it at frequent enough time intervals or to enhance particular local aspects of the initial analyses. In many instances, observations and extrapolations are still considered to be more important than numerical guidance in the very short range.
In this paper, an isentropic forecast technique is used to provide temporally and spatially detailed short-term advective forecasts of temperature, moisture, and wind changes. While geostrophic potential vorticity conservation is used to simplify the model, the advective computations can use both geostrophic and ageostrophic wind data. The inclusion of pronounced baroclinic structures in the detailed initial isentropic analyses allows the model to preserve large observed vertical and horizontal wind shears, to monitor local stability changes, and to detect areas of strong subsidence and overrunning.
A series of short-range forecasts of the preconvective environment associated with severe convection is discussed. High time frequency fields of midtropospheric static stability, low-level moisture and temperature, tropopause height, and conventional stability indices are presented and combined with observed surface data to provide updated stability and buoyancy guidance. In addition, forecasted winds are used to advect VAS mid- and low-level moisture imagery, which can be used to predict areas of changing convective potential and extend the lead time required to issue forecasts for severe convective storms.
Abstract
The recent advancement of mini- and microcomputers into the local-work environment can provide local forecast offices with the capability to run simple numerical models for specific nowcasting and short-term forecast needs. While the capabilities of sophisticated, centralized modeling systems continue to progress, short-term forecasts are hampered by a number of inadequacies in this guidance, ranging from numerical deficiencies of the models to the inability to access the gridded model output in a timely manner and view it at frequent enough time intervals or to enhance particular local aspects of the initial analyses. In many instances, observations and extrapolations are still considered to be more important than numerical guidance in the very short range.
In this paper, an isentropic forecast technique is used to provide temporally and spatially detailed short-term advective forecasts of temperature, moisture, and wind changes. While geostrophic potential vorticity conservation is used to simplify the model, the advective computations can use both geostrophic and ageostrophic wind data. The inclusion of pronounced baroclinic structures in the detailed initial isentropic analyses allows the model to preserve large observed vertical and horizontal wind shears, to monitor local stability changes, and to detect areas of strong subsidence and overrunning.
A series of short-range forecasts of the preconvective environment associated with severe convection is discussed. High time frequency fields of midtropospheric static stability, low-level moisture and temperature, tropopause height, and conventional stability indices are presented and combined with observed surface data to provide updated stability and buoyancy guidance. In addition, forecasted winds are used to advect VAS mid- and low-level moisture imagery, which can be used to predict areas of changing convective potential and extend the lead time required to issue forecasts for severe convective storms.
On the Performance of Airborne Meteorological Observations against Other In Situ MeasurementsAbstract
Routine in situ observations of the atmosphere taken in flight by commercial aircraft provide atmospheric profiles with greater temporal density and, in many parts of the country, at more locations than the operational radiosonde network. Thousands of daily temperature and wind observations are provided by largely complementary systems, the Airborne Meteorological Data Relay (AMDAR) and the Tropospheric Airborne Meteorological Data Reporting (TAMDAR). All TAMDAR aircraft also measure relative humidity while a subset of AMDAR aircraft are equipped with the Water Vapor Sensing System (WVSS) measure specific humidity. One year of AMDAR/WVSS and TAMDAR observations are evaluated against operational National Weather Service (NWS) radiosondes to characterize the performance of these systems in similar environments. For all observed variables, AMDAR reports showed both smaller average differences and less random differences with respect to radiosondes than the corresponding TAMDAR observations. Observed differences were not necessarily consistent with known radiosonde biases. Since the systems measure different humidity variables, moisture is evaluated in both specific and relative humidity using both aircraft and radiosonde temperatures to derive corresponding moisture variables. Derived moisture performance is improved when aircraft-based temperatures are corrected prior to conversion. AMDAR observations also show greater consistency between different aircraft than TAMDAR observations do. The small variability in coincident WVSS humidity observations indicates that they may prove more reliable than humidity observations from NWS radiosondes.
Abstract
Routine in situ observations of the atmosphere taken in flight by commercial aircraft provide atmospheric profiles with greater temporal density and, in many parts of the country, at more locations than the operational radiosonde network. Thousands of daily temperature and wind observations are provided by largely complementary systems, the Airborne Meteorological Data Relay (AMDAR) and the Tropospheric Airborne Meteorological Data Reporting (TAMDAR). All TAMDAR aircraft also measure relative humidity while a subset of AMDAR aircraft are equipped with the Water Vapor Sensing System (WVSS) measure specific humidity. One year of AMDAR/WVSS and TAMDAR observations are evaluated against operational National Weather Service (NWS) radiosondes to characterize the performance of these systems in similar environments. For all observed variables, AMDAR reports showed both smaller average differences and less random differences with respect to radiosondes than the corresponding TAMDAR observations. Observed differences were not necessarily consistent with known radiosonde biases. Since the systems measure different humidity variables, moisture is evaluated in both specific and relative humidity using both aircraft and radiosonde temperatures to derive corresponding moisture variables. Derived moisture performance is improved when aircraft-based temperatures are corrected prior to conversion. AMDAR observations also show greater consistency between different aircraft than TAMDAR observations do. The small variability in coincident WVSS humidity observations indicates that they may prove more reliable than humidity observations from NWS radiosondes.
Abstract
A 23–24 February 1975 case study is made comparing the results achieved using Nimbus 5 satellite temperature, profiles with those obtained from radiosonde data and the initial hour data of the Limited Area Fine Mesh (LFM) model of the National Meteorological Center. An objective analysis technique is used to construct and analyze isotropic cross sections through an intense baroclinic zone. A cross section based on 1700 GMT Nimbus 5 soundings is compared with those based on 1200 and 0000 GMT radiosonde and LFM data. Geostrophic shear calculations are used to compare the thermal gradients for various isobaric layers obtained from the three data acts. The Nimbus 5 results show somewhat less detail than those based on the radiosonde data, but wore than those obtained from the LPM data. Comparisons of the mean temperature in various isobaric layers for the three time periods indicate that the 1700 GMT Nimbus 5 data appear to be consistent with the changing synoptic pattern. Estimates of the wind components normal to the cross sections are obtained using 1) the geostrophic wind calculated from Nimbus 5 data, 2) the observed winds which are enhanced by the geostrophic shear obtained from the radiosonde data, and 3) the initial-hour LFM winds. The wind estimates also indicate that the Nimbus 5 data provide results which agree with the evolving synoptic situation. In general, the results suggest that the insertion into numerical models of satellite-derived mean thermal gradients calculated for 100–200 mb thick layers, rather than mean temperatures, may facilitate the use of satellite soundings.
Abstract
A 23–24 February 1975 case study is made comparing the results achieved using Nimbus 5 satellite temperature, profiles with those obtained from radiosonde data and the initial hour data of the Limited Area Fine Mesh (LFM) model of the National Meteorological Center. An objective analysis technique is used to construct and analyze isotropic cross sections through an intense baroclinic zone. A cross section based on 1700 GMT Nimbus 5 soundings is compared with those based on 1200 and 0000 GMT radiosonde and LFM data. Geostrophic shear calculations are used to compare the thermal gradients for various isobaric layers obtained from the three data acts. The Nimbus 5 results show somewhat less detail than those based on the radiosonde data, but wore than those obtained from the LPM data. Comparisons of the mean temperature in various isobaric layers for the three time periods indicate that the 1700 GMT Nimbus 5 data appear to be consistent with the changing synoptic pattern. Estimates of the wind components normal to the cross sections are obtained using 1) the geostrophic wind calculated from Nimbus 5 data, 2) the observed winds which are enhanced by the geostrophic shear obtained from the radiosonde data, and 3) the initial-hour LFM winds. The wind estimates also indicate that the Nimbus 5 data provide results which agree with the evolving synoptic situation. In general, the results suggest that the insertion into numerical models of satellite-derived mean thermal gradients calculated for 100–200 mb thick layers, rather than mean temperatures, may facilitate the use of satellite soundings.
Abstract
No abstract available.
Abstract
No abstract available.
