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RSMC Tokyo-Typhoon Center

Technical Review No.10  (March 2008)

  Revision of JMA's Early Stage Dvorak Analysis and Its Use to Analyze Tropical Cyclones in the Early Developing Stage
  Kenji KISHIMOTO
  National Typhoon Center, Japan Meteorological Agency

 This report follows Kishimoto et al. (2007). The Japan Meteorological Agency (JMA) conducted verification of the behaviors of past tropical cyclones (TCs) for the purpose of developing the diagnosis of T-number 0.5 (T0.5). The results indicate that T0.5 diagnosis is valid for satellite image analysis for TCs in the early developing stage (early stage Dvorak analysis: EDA). Organized convective cloud systems (OCCSs) diagnosed as T0.0 or T0.5 can be recognized as follows:
  • Most OCCSs are not yet determined as tropical depressions (TDs) when they are first diagnosed as T0.0.
  • OCCSs are likely to be determined as TDs when they are first diagnosed as T0.5.

  •   In summer 2007, based on the above results and Kishimoto et al. (2007), JMA revised EDA. The main part of this revision involved the addition of T0.5 diagnosis to the former EDA, which consisted of OCCS detection, T1.0 diagnosis and T1.5/2.0 diagnosis. In addition, JMA revised the criteria for determining the TC grade using EDA results. Analysis of TCs in the early developing stage using the revised EDA is explained through the example of the TD that became USAGI (0705).
       Text [PDF 1.3MB]

       The Possibility of Determining Whether Organized Cloud Clusters Will Develop into Tropical Storms by Detecting Warm Core Structures from Advanced Microwave Sounding Unit Observations
       Kotaro BESSHO, Tetsuo NAKAZAWA
       Meteorological Research Institute, Japan Meteorological Agency
       Shuji NISHIMURA
       National Typhoon Center, Japan Meteorological Agency
       Koji KATO
       Meteorological Satellite Center, Japan Meteorological Agency

      The air temperature profiles of organized cloud clusters developing or not developing into tropical storms (TSs) over the western North Pacific in 2004 were investigated from Advanced Microwave Sounding Unit (AMSU) observations and the results of Dvorak analyses for the cloud clusters. First, typical temperature profiles of the clusters developing or not developing into TSs were compared. From this comparison, positive temperature anomalies in the upper troposphere were found in both clusters, while the values and spatial sizes of the anomalies for the clusters that developed into TS were larger than those for the ones that did not. Statistical analysis was then performed on the temperature anomalies near the center of all clusters retrieved from AMSU observational data. The average anomalies increased along with the intensity of the clusters indicated by the T-number, as estimated using the Dvorak technique. Time series analysis of temperature anomalies in the upper levels of the clusters was performed, and warm core structures were defined by the threshold derived from these anomalies. Using this definition, almost 70% of the clusters that had warm cores developed into TSs, while 85% of those that did not finally dissipated without such development. For the warm-core clusters that developed into TSs, the lead time from the detection of their warm core using AMSU observations to their recognition as TS was 27.7 hours. It is suggested that there is a strong possibility of detecting and forecasting the genesis of TSs using air temperature anomalies derived from AMSU data.
       Text [PDF 1.3MB]

       Analysis of Tropical Cyclones Using Microwave Satellite Imagery
       Jun-ichi ASANO
       Meteorological College, Japan Meteorological Agency
       Shuji NISHIMURA
       National Typhoon Center, Japan Meteorological Agency
       Koji KATO, Kouki MOURI, Shiro YOSHIDA, Takeshi ENDO, Kohei OOTUBO, Akihiro SHIMIZU, Ryo OYAMA
       Meteorological Satellite Center, Japan Meteorological Agency
       Sadao SAITOH
       Earth Observation Research Center, Japan Aerospace Exploration Agency

      The Meteorological Satellite Center of the Japan Meteorological Agency has estimated center positions and intensities of tropical cyclones by the Dvorak method, which uses infrared and visible imagery from the MTSAT-1R geostationary meteorological satellite. While the Dvorak method is the most popular technique for analyzing tropical cyclones through infrared and visible imagery, it is not good at estimating the center positions of tropical cyclones that are covered by upper cirrus cloud and do not have a clear eye in their developing stage, especially during periods when visible imagery is not available.
      To combat this difficulty, we used microwave imagery from the AMSR-E system on board the Aqua earth-observing satellite to analyze the inner structures of tropical cyclones, which cannot be seen in infrared or visible imagery. We also developed a method to estimate center positions of tropical cyclones using this microwave imagery analysis. Verification using the tropical cyclones from 2003 to 2005 showed that the accuracy of center positions estimated by microwave imagery was almost the same as that obtained by radar observation. As a result, our method was proven to be an effective means of improving the accuracy of center positions estimated by the Dvorak method.
       Text [PDF 2.7MB]

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