Ralph A. Petersen

The Computation of Isentropic Atmospheric Trajectories Using a “Discrete Model” Formulation

Abstract An explicit technique for computing atmospheric trajectories, based on Greenspans 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.

Overview of the NMC Production Suite

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.

Comparisons of Satellite-Derived Atmospheric Motion Vectors, Rawinsondes, and NOAA Wind Profiler Observations

Abstract Geostationary satellite-derived atmospheric motion vectors (AMVs) have been used over several decades in a wide variety of meteorological applications. The ever-increasing horizontal and vertical resolution of numerical weather prediction models puts a greater demand on satellite-derived wind products to monitor flow accurately at smaller scales and higher temporal resolution. The focus of this paper is to evaluate the accuracy and potential applications of a newly developed experimental mesoscale AMV product derived from Geostationary Operational Environmental Satellite (GOES) imagery. The mesoscale AMV product is derived through a variant on processing methods used within the University of Wisconsin—Madison Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS) AMV algorithm and features a significant increase in vector density throughout the troposphere and lower stratosphere over current NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) processing me...

Assimilation of Surface-Based Boundary Layer Profiler Observations during a Cool-Season Weather Event Using an Observing System Simulation Experiment. Part II: Forecast Assessment

AbstractIn this study, an Observing System Simulation Experiment was used to examine how the assimilation of temperature, water vapor, and wind profiles from a potential array of ground-based remote sensing boundary layer profiling instruments impacts the accuracy of atmospheric analyses when using an ensemble Kalman filter data assimilation system. Remote sensing systems evaluated during this study include the Doppler wind lidar (DWL), Raman lidar (RAM), microwave radiometer (MWR), and the Atmospheric Emitted Radiance Interferometer (AERI). The case study tracked the evolution of several extratropical weather systems that occurred across the contiguous United States during 7–8 January 2008. Overall, the results demonstrate that using networks of high-quality temperature, wind, and moisture profile observations of the lower troposphere has the potential to improve the accuracy of wintertime atmospheric analyses over land. The impact of each profiling system was greatest in the lower and middle troposphere...

Assessment of VAS Soundings in the Analysis of a Preconvective Environment

Abstract Retrievals from the VISSR Atmospheric Sounder (VAS) an combined with conventional data to assess the impact of geosynchronous satellite soundings upon the analysis of a pre-convective environment over the central United States on 13 July 1981. VAS retrievals of temperature, dewpoint, equivalent potential temperature, precipitable water, and lifted index are derived with 30 km resolution at 3 hour intervals. When VAS fields are combined with analyses from conventional data sources regions with convective instability are more clearly delineated prior to the rapid development of the thunderstorms. The retrievals differentiate isolated areas in which most air extends throughout the lower troposphere (and are therefore more conducive for the development of deep convective storms) from those regions where moisture is confined to a thin layer near the earths surface (where convection is less likely to occur). The analyses of the VAS retrievals identify significant spatial gradients and temporal changes...

A Report on the Upper-Level Wind Conditions Preceding and During the Shuttle Challenger (STS 51L) Explosion

The synoptic-scale weather conditions preceding and following the ill-fated Space Shuttle Challenger launch are documented, with particular emphasis on the upper-level winds for central and northern Florida. Operational radiosonde data collected by the National Weather Service, visible and infrared imagery from the Geostationary Operational Environmental Satellite, and water-vapor imagery from the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder, ozone data collected by the Total Ozone Mapping Spectrometer aboard the Nimbus-7, and soundings collected at Cape Canaveral (XMR) are described. Analyses derived from these data sets point to the juxtaposition of two distinct jet-stream systems (a polar-front jet [PFJ] and a subtropical jet [STJ]) over north-central Florida on the morning of the launch. Both jets were characterized by regions of significant vertical wind shear, which was especially strong above and below the core of the STJ. Data from a radiosonde released at Cape Canaveral 10 mi...

Demonstration of a GOES-R Satellite Convective Toolkit to “Bridge the Gap” between Severe Weather Watches and Warnings: An Example from the 20 May 2013 Moore, Oklahoma, Tornado Outbreak

AbstractWith the launch of the Geostationary Operational Environmental Satellite–R (GOES-R) series in 2016, there will be continuity of observations for the current GOES system operating over the Western Hemisphere. The GOES-R Proving Ground was established in 2008 to help prepare satellite user communities for the enhanced capabilities of GOES-R, including new instruments, imagery, and products that will have increased spectral, spatial, and temporal resolution. This is accomplished through demonstration and evaluation of proxy products that use current GOES data, higher-resolution data provided by polar-orbiting satellites, and model-derived synthetic satellite imagery. The GOES-R demonstration products presented here, made available to forecasters in near–real time (within 20 min) via the GOES-R Proving Ground, include the 0–9-h NearCast model, 0–1-h convective initiation probabilities, convective cloud-top cooling, overshooting top detection, and a pseudo–Geostationary Lightning Mapper total lightning...

A VAS-numerical model impact study using the Gal-Chen variational approach

Abstract Numerical experiments are conducted to assess the impact of incorporating temperature data from the VISSR Atmospheric Sounder (VAS) into a regional-scale numerical model using an assimilation technique developed by Gal-Chen. The technique uses a three-dimensional variational approach to combine the VAS observations with model temperature fields during the numerical integration. A nudging technique is also tested, whereby the model temperature field is constrained toward the VAS “updated” values during the assimilation cycle. Results of the experiments indicate that the Gal-Chen assimilation technique successfully combines actual VAS temperature observations with the dynamically balanced model fields without destabilizing the model during the assimilation cycle. Furthermore, increasing the temporal frequency of VAS temperature insertions during the assimilation cycle enhances the impact on the model forecast through successively longer forecast periods. These results support the conclusions of ear...

On the Impact and Benefits of AMDAR Observations in Operational Forecasting—Part I: A Review of the Impact of Automated Aircraft Wind and Temperature Reports

AbstractThis paper reviews the impact of World Meteorological Organization (WMO) Aircraft Meteorological Data Relay (AMDAR) observations on operational numerical weather prediction (NWP) forecasts at both regional and global scales that support national and local weather forecast offices across the globe. Over the past three decades, data collected from commercial aircraft have helped reduce flight-level wind and temperature forecast errors by nearly 50%. Improvements are largest in 3–48-h forecasts and in regions where the automated reports 1) are most numerous, 2) cover a broad area, and 3) are available at multiple levels (e.g., made during aircraft ascent and descent). Improvements in weather forecasts due to these data have already had major impacts on a variety of aspects of airline operations, ranging from fuel savings from improved wind and temperature forecasts used in flight planning to passenger comfort and safety due to better awareness of en route and near-terminal weather hazards. Aircraft w...

The Effect of Snow Cover on the Regional Analysis and Forecast System (RAFS) Low-Level Forecasts

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 earths 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.