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The Dvorak technique (developed between 1969 and 1984 by Vernon Dvorak) is a widely used system to estimate tropical cyclone intensity (which includes tropical depression, tropical storm, and hurricane/typhoon/intense tropical cyclone intensities) based solely on visible and infrared satellite images. Within the Dvorak satellite strength estimate for tropical cyclones, there are several visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity. The primary patterns used are curved band pattern (T1.0-T4.5), shear pattern (T1.5-T3.5), central dense overcast (CDO) pattern (T2.5-T5.0), central cold cover (CCC) pattern, banding eye pattern (T4.0-T4.5), and eye pattern (T4.5 - T8.0). Both the central dense overcast and embedded eye pattern use the size of the CDO. The CDO pattern intensities start at T2.5, equivalent to minimal tropical storm intensity (40 mph, 65 km/h). The shape of the central dense overcast is also considered. The eye pattern utilizes the coldness of the cloud tops within the surrounding mass of thunderstorms and contrasts it with the temperature within the eye itself. The larger the temperature difference is, the stronger the tropical cyclone. Once a pattern is identified, the storm features (such as length and curvature of banding features) are further analyzed to arrive at a particular T-number. The CCC pattern indicates little development is occurring, despite the cold cloud tops associated with the quickly evolving feature. Several agencies issue Dvorak intensity numbers for tropical cyclones and their precursors, including the National Hurricane Center's Tropical Analysis and Forecast Branch (TAFB), the NOAA/NESDIS Satellite Analysis Branch (SAB), and the Joint Typhoon Warning Center at the Naval Meteorology and Oceanography Command in Pearl Harbor, Hawaii. ==Evolution of the method== The initial development of this technique occurred in 1969 by Vernon Dvorak, using satellite pictures of tropical cyclones within the northwest Pacific ocean. The system as it was initially conceived involved pattern matching of cloud features with a development and decay model. As the technique matured through the 1970s and 1980s, measurement of cloud features became dominant in defining tropical cyclone intensity and central pressure of the tropical cyclone's low-pressure area. Use of infrared satellite imagery led to a more objective assessment of the strength of tropical cyclones with eyes, using the cloud top temperatures within the eyewall and contrasting them with the warm temperatures within the eye itself. Constraints on short term intensity change are used less frequently than they were back in the 1970s and 1980s. The central pressures assigned to tropical cyclones have required modification, as the original estimates were 5-10 hPa (0.15-0.29 inHg) too low in the Atlantic and up to 20 hPa (0.59 inHg) too high in the northwest Pacific. This led to the development of a separate wind-pressure relationship for the northwest Pacific, devised by Atkinson and Holliday in 1975, then modified in 1977.〔 As human analysts using the technique lead to subjective biases, efforts have been made to make more objective estimates using computer programs, which have been aided by higher-resolution satellite imagery and more powerful computers. Since tropical cyclone satellite patterns can fluctuate over time, automated techniques use a six-hour averaging period to lead to more reliable intensity estimates. Development of the objective Dvorak technique began in 1998, which performed best with tropical cyclones that had eyes (of hurricane or typhoon strength). It still required a manual center placement, keeping some subjectivity within the process. By 2004, an advanced objective Dvorak technique was developed which utilized banding features for systems below hurricane intensity and to objectively determine the tropical cyclone's center. A central pressure bias was uncovered in 2004 relating to the slope of the tropopause and cloud top temperatures which change with latitude that helped improve central pressure estimates within the objective technique. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dvorak technique」の詳細全文を読む スポンサード リンク
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