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Ted L. Tsui and Ronald J. Miller

Abstract

The Joint Typhoon Warning Center's (JTWC) official and objective aid forecasts for the western North Pacific tropical cyclones during 1978–85 are evaluated. Forecast accuracy is measured by the forecast error, cross-track error and along-track error with respect to the best track of the tropical cyclone. In addition, data are stratified by the storm's intensity for further detailed comparisons. Considering all stratifications, two aids emerged as best for the entire data period: the Half Persistence and Climatology (HPAC) and the One-way interactive Tropical Cyclone Model (OTCM). The HPAC is superior to OTCM for the tropical storm forecasts, but OTCM is superior for the typhoon and super-typhoon forecasts.

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Ernest C. Kung and Ted L. Tsui

Abstract

The balance of kinetic energy under severe storm conditions is investigated with a subsynoptic-scale upper-air network. The general shape of vertical profiles of the kinetic energy.generation and dissipation is very similar to that observed in well-developed major cyclones. The overall average magnitude of the observed energy transformations in the severe storm area is comparable to that of major synoptic-scale cyclones, but for a given storm the magnitude of energy transformations may vary widely depending on the existence and strength of mesoconvective systems in the area.

The balance of kinetic energy is also studied for the transient disturbances detected with the subsynoptic- scale upper-air network. Energetics features for those disturbances are depicted and discussed. The mid and lower troposphere appear to be the major source region of eddy kinetic energy.

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Ted L. Tsui and Ernest C. Kung

Abstract

The energy transformations ore studied with a subsynoptic-scale upper air network for three types of severe storm environments under convective, nonconvective and frontal situations.

The environment of the convective storms is most active energetically with intense generation and dissipation of kinetic energy taking place in the upper layer of the atmosphere. In the case of the non-convective environment, a strong adiabatic destruction of kinetic energy through the cross-isobaric flow takes place in the upper layer of the atmosphere. In the frontal cases the upper layer of the atmosphere becomes energetically inactive for the observed scale in terms of the gross energy budget. Examination of the kinetic energy budget during the thunderstorm passage indicates the existence of subsynoptic-scale areas of adiabatic generation and destruction of kinetic energy with the maximum destruction in the middle and upper layers in the area of the maximum storm intensity.

The eddy energy transformations in the disturbances are intensive in the active convective environment, and a significant amount of eddy kinetic energy is derived through the local baroclinic conversion process.

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Patrick A. Harr, Ted L. Tsui, and L. Robin Brody

Abstract

Many numerical model verification schemes are handicapped by their inability to separate non-systematic errors and systematic errors. In this study, for a specific synoptic event, a statistical method is described to determine a minimum number of cases which can be averaged to represent numerical forecast errors which are truly systematic and not smoothed fields of rapidly varying non-systematic errors.

Error patterns derived from forecasts and observations stored at Fleet Numerical Oceanography Center are used to compare a systematic error pattern, defined by the total number of available cases with subset error patterns to determine the minimum number of cases needed to filter out the unwanted non-systematic error components. The analysis indicates that a minimum of 8 cases must be averaged to adequately identify systematic errors in a 24 h forecast of a Shanghai Low. A minimum of 5 cases are needed for a 72 h forecast of the same event. Error patterns are identified by contours of the Student's t statistic calculated at each grid point. This contour pattern objectively determines the significance of the forecast errors and is shown to be a very useful method of portraying, systematic forecast errors.

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William M. Gray, Charles Neumann, and Ted L. Tsui

The impact of aircraft reconnaissance on tropical cyclone (TC) observation and forecasting is assessed. The motivation for this assessment is the termination of Department of Defense (DOD) aircraft reconnaissance in the northwest Pacific in 1987 and the suggestion by some DOD officials that it may also be technically feasible to greatly reduce or similarly discontinue DOD aircraft reconnaissance in the Atlantic. In response thereto, the American Meteorological Society (AMS) Committee on Tropical Meteorology and Tropical Cyclones recommended that a specialized ad hoc group be formed to study the technical aspects of this issue. The resulting study presented here focuses on the issue of the extent to which reliable TC warnings can be continued along the United States hurricane-vulnerable coastline without observations from aerial reconnaissance and summarizes relevant information contained in recent studies prompted by the termination of reconnaissance in the western North Pacific. Primary attention is given to the technical and meteorological aspects of this question and economic and societal aspects receive only brief attention.

Although it is recognized that weather satellites are absolutely essential for tropical cyclone observation on a global scale, it is found that independent satellite measurements of position, intensity, outer wind distribution, and ambient steering current of tropical cyclones are sometimes degraded from what can be provided by aircraft over a limited but operationally significant area. Such degraded observational data can significantly impact forecasts of these quantities.

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Ronald J. Miller, Ann J. Schrader, Charles R. Sampson, and Ted L. Tsui

Abstract

The U.S. Navy Automated Tropical Cyclone Forecasting System (ATCF) is an IBM-AT compatible software package developed for the Joint Typhoon Warning Center (JTWC), Guam. ATCF is designed to assist forecasters with the process of making tropical cyclone forecasts. The system graphically displays tropical cyclone track, fix, and forecast information, as well as synoptic fields and rawinsonde observations. Using the data base, ATCF also generates menages such as the tropical cyclone warning message. The computing power of the personal computer allows ATCF to produce products such as western North Pacific CLIPER and objective best track guidance. ATCF automatically saves all tropical cyclone data, computes real-time and post-storm forecast error statistics, and allows forecasters access to any past track data since 1945. ATCF standardizes the tropical cyclone forecasting procedure, ensuring that forecasters will not neglect consideration of important decisional steps. It also automates consuming tasks such as manual plotting of forecasts and logging data on clipboards. The system, while designed specifically for JTWC, is extremely flexible and has been distributed outside the U.S. Navy.

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