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H. M. Johnson and Donald R. Cochran

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Linda M. Keller and Donald R. Johnson

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Time series of hemispheric available potential (A) and kinetic (K) energies were used to examine the results of a series of observing system simulation experiments that were performed with the Goddard Laboratory for Atmospheres model to determine the impact of the proposed space-based wind profiler on forecast accuracy. The simulated data for the series of 5-day forecasts were produced from a 20-day integration using the ECMWF model, which was also used to produce the verification forecast for the 5-day period. The three simulated observational sets of data that represented conventional observations, satellite-retrieval temperatures, and wind profiles were produced by NMC.

The results in the Northern Hemisphere show that the magnitudes of A and K from the simulation forecasts are quite similar to each other and are uniformly higher than the verification forecast, reflecting systematic differences in the energy levels of the two models. In the Southern Hemisphere, differences in magnitude of A between simulation and verification forecasts are larger than in the Northern Hemisphere. The time series for K shows greater diversity in magnitude among the simulation forecasts, with all the simulation forecasts for K being higher than the verification forecast. The S 1 skill scores and root-mean-square (rms) differences reveal little variation in the accuracy of the forecasts among the three simulation datasets in the Northern Hemisphere. In the Southern Hemisphere, however, forecasts using satellite temperature and wind-profiler data have much smaller rms differences and S 1 scores, indicating an improvement in forecast accuracy over conventional observations. The addition of wind-profiler data provides the greatest improvement in forecast accuracy.

Geographical distributions of vertically integrated eddy A (Ae and K in the Northern Hemisphere reveal that these quantities in the three simulation forecasts are more similar to each other than with the verification forecast. In the Southern Hemisphere, the geographical distributions of Ae and K are more varied with the wind-profiler dataset producing a forecast closest to the verification forecast. In general, the impact of the addition of wind-profiler data on forecast accuracy of energy parameters is negligible in the Northern Hemisphere but distinctly positive in the Southern Hemisphere.

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J. M. Vergin, D. R. Johnson, and R. Atlas

Abstract

The results of a quasi-Lagrangian diagnostic study of two 72 h Goddard Laboratory for Atmospheric Sciences (GLAS) model cyclone predictions from 0000 GMT 19 February 1976 are presented and compared with observed results. One model forecast (SAT) was generated from initial conditions which included satellite sounding data, and the other model forecast (NOSAT) was generated from initial conditions that excluded satellite sounding data. Examination of the mass and angular momentum budget statistics for the SAT and NOSAT forecasts reveals substantial differences. The improvement in the SAT forecast is established from the more realistic SAT budget statistics, and results from the modifications of initial atmospheric structure due to satellite information.

The assimilation of satellite data caused modifications of the horizontal mass and eddy angular momentum transports at the zero hour. The assimilation of satellite data resulted in colder temperatures and weaker stabilities in the lower layers of the northwest quadrant of the budget volume, and thus an improved structure of the cold polar air mass over a relatively warm ocean surface. In the southwest quadrant of the budget volume, the SAT assimilation produced an increase in the stability of the middle and lower layers and an increase in temperatures throughout much of the troposphere. These modifications in the temperature structure were the primary reasons for the improved mass and eddy angular momentum transports which contributed to the better SAT forecast for the cyclone event.

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R. H. SIMPSON, NEIL FRANK, DAVID SHIDELER, and H. M. JOHNSON

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No Abstract Available.

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Tom H. Zapotocny, Donald R. Johnson, and Fred M. Reames

Abstract

In an initial effort in regional numerical weather prediction, results from the University of Wisconsin isentropic-sigma (UW θ−σ) hybrid model and an “identical” sigma model are compared. The two main objectives are to demonstrate the capability of the UW θ−σ model for regional numerical weather prediction and to identify advantages of the hybrid model in simulating atmospheric water vapor transport and precipitation relative to the sigma model.

The 72-h simulations produced by the two models extend over a region covering the western Pacific Ocean, North America, and the western Atlantic Ocean. The simulations begin at 0000 UTC 13 January 1979, a period during which an intense Chicago blizzard (sometimes called the Mayor Jane Byrne storm) develops over the central United States. This period also includes the rapid development of a cyclone in the western Pacific Ocean.

Results using the Global Weather Experiment (GWE) ECMWF level IIIB data as initial and verification data indicate that both models produce reasonable and similar 72-b simulations, with the UW θ−σ model mass and momentum distributions being slightly more accurate than the sigma model. Of particular importance for the Chicago blizzard is that the UW θ−σ model more accurately simulates water vapor transport northward from the Gulf of Mexico and westward from the Atlantic Ocean. As a result, the hybrid model more accurately simulates observed precipitation, especially over the northeastern United States and southeastern Canada.

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R. H. SIMPSON, NEIL FRANK, DAVID SHIDELER, and H. M. JOHNSON

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No Abstract Available.

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Tom H. Zapotocny, Donald R. Johnson, and Fred M. Reames

Abstract

The description of a global version of the University of Wisconsin (UW) hybrid isentropic-sigma (θ − σ) model and the results from an initial numerical weather prediction experiment are presented in this paper. The main objectives of this initial test are to 1) discuss θ − σ model development and computer requirements, 2) demonstrate the ability of the UW θ − σ model for global numerical weather prediction using realistic orography and parameterized physical processes, and 3) compare the transport of an inert trace constituent against a nominally “identical” sigma (σ) coordinate model. Initial and verifying data for the 5-day simulations presented in this work were supplied by the Goddaird Earth Observing System (GEOS-1) data assimilation system. The time period studied is 1–6 February 1985.

This validation experiment demonstrates that the global UW θ − σ model produces a realistic 5-day simulation of the mass and momentum distributions when compared to both the identical σ model and GEOS-1 verification. Root-mean-square errors demonstrate that the θ − σ model is slightly more accurate than the nominally identical σ model with respect to standard synoptic variables. Of particular importance, the UW θ − σ model displays a distinct advantage over the conventional σ model with respect to the prognostic simulation of inert trace constituent transport in amplifying baroclinic waves of the extratropics. This is especially true in the upper troposphere and stratosphere where the spatial integrity and conservation of an inert trace constituent is severely compromised in the a model compared to the θ − σ model.

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H. L. Johnson Jr., R. D. Hart, M. A. Lind, R. E. Powell, and J. L. Stanford

Abstract

Thunderstorm radio noise measurements at several frequencies in the range 0.01–74 MHz have been made with specially designed remote recording stations in Iowa. The data were recorded during the spring and summer of 1974 when a series of severe storm systems produced a great number of large hail and tornado reports in Iowa. Computer analyses were made of nearly a billion bits of data, corresponding to 170 h of real-time recordings. Careful compilations of surface severe weather reports, hail damage information from insurance companies, and studies on the Des Moines WSR-57 radar echoes were compared with the analyzed radio noise data. The results include the following:

1) In agreement with earlier work, large‐amplitude radio noise impulse rates were found to he generally good indicators of thunderstorm severity. Although the majority of the radio energy radiated from major lightning strokes occurs in the 0.01 MHz range, this frequency was found to be a poor indicator of storm severity; the higher frequencies (megahertz range) were considerably better. The character of the noise appears similar at 2.5 and 74 MHz.

2) In at least five cases, tornadic events correlated in time with radio noise count rate peaks. One funnel cloud was reported equidistant at 60 km from two recording stations and coincident with count rate peaks at both stations, lending credence to the idea that the peak was associated with the storm occurrence, rather than with corona or other local effects.

3) No unusual radio noise was recorded during the lifetime of a small, verified tornado at 19 km range. In addition, the count rates for its parent thunderstorm would not have indicated severity.

In spite of inherent atmospheric variableness, the radio noise technique is a useful complementary indicator of storm severity.

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Donald R. Johnson, Tom H. Zapotocny, Fred M. Reames, Bart J. Wolf, and R. Bradley Pierce

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The primary objectives of this study are threefold: 1) to compare simulators of dry and moist baroclinic development from 10-and 22-layer hybrid isentropic-sigma coordinate models with those from 11-, 27-, and 35-layer sigma coordinate models; 2) to examine the ability of the models to transport water vapor and simulate equivalent potential temperature θe; and 3) to compare predictions of the timing, location, and amount of precipitation. A model's capability to predict precipitation sterns from the accuracy of its simulation of the joint distribution of mass, potential temperature, and water vapor throughout the model domain. In a series of experiments to compare simulations of precipitation, several analytic distributions of water vapor are specified initially. The water vapor distributions include a “cylinder”extending vertically throughout the atmosphere and “lenses” within isentropic, sigma, and isobaric layers. The effect of increased horizontal resolution are also studied.

Results indicate that when the relative humidity is vertically uniform through a substantial extent of the atmosphere, all the models produce very similar precipitation distributions. However, when water vapor is confined to relatively shallow layers, the ability of the sigma coordinate models to simulate the timing, location, and amount of precipitation is severely compromised. Furthermore, the 10-layer hybrid model conserves θe to a higher degree of accuracy and simulates a more realistic evolution of precipitation even when compared to results from sigma models with increased vertical and horizontal resolution. In all instances, the experiments demonstrate that advantages reside in prediction of precipitation with the hybrid model. Both theoretical and conceptual bases for thew differences are provided.

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Tom H. Zapotocny, Allen J. Lenzen, Donald R. Johnson, Todd K. Schaack, and Fred M. Reames

Abstract

Five- and 10-day inert trace constituent distributions prognostically simulated with the University of Wisconsin (UW) hybrid isentropic–sigma (θσ) model, the nominally identical UW sigma (σ) model, and the National Center for Atmospheric Research Community Climate Model 2 (CCM2) are analyzed and compared in this study. The UW θσ and σ gridpoint models utilize the flux form of the primitive equations, while CCM2 is based on the spectral representation and uses semi-Lagrangian transport (SLT) for trace constituents. Results are also compared against a version of the CCM that uses spectral transport for the trace constituent. These comparisons 1) contrast the spatial and temporal evolution of the filamentary transport of inert trace constituents simulated with the UW θσ and σ models against a “state of the art” GCM under both isentropic and nonisentropic conditions and 2) examine the ability of the models to conserve the initial trace constituent maximum value during 10-day integrations.

Results show that the spatial distributions of trace constituent evolve in a similar manner, regardless of the transport scheme or model type. However, when compared to the UW θσ model’s ability to simulate filamentary structure and conserve the initial trace constituent maximum value, results from the other models in this study indicate substantial spurious dispersion. The more accurate conservation demonstrated with the UW θσ model is especially noticeable within extratropical amplifying baroclinic waves, and it stems from the dominance of two-dimensional, quasi-horizontal isentropic exchange processes in a stratified baroclinic atmosphere. This condition, which largely precludes spurious numerical dispersion associated with vertical advection, is unique to isentropic coordinates. Conservation of trace constituent maxima in sigma coordinates suffers from the complexity of, and inherent need for, resolving three-dimensional transport in the presence of vertical wind shear during baroclinic amplification, a condition leading to spurious vertical dispersion. The experiments of this study also indicate that the shape-preserving SLT scheme used in CCM2 further reduces conservation of the initial maximum value when compared to the spectral transport of trace constituents, although the patterns are more coherent and the Gibbs phenomenon is eliminated.

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