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RSMC Tokyo-Typhoon Center

Technical Review No.7  (March 2004)

  Improvement of the JMA Typhoon Model by Using New Physical Processes
  Ryota SAKAI, Takuya HOSOMI
  Numerical Prediction Division, Japan Meteorological Agency

 The Typhoon Model (TYM) with a new physical process package was operationally implemented in July 2003 at the Japan Meteorological Agency (JMA). In this package, (1) a prognostic cloud scheme based on Smith (1990) and (2) a radiation scheme including the direct effect of aerosols were newly introduced. In addition to these effect, (3) a prognostic Arakawa-Schubert cumulus parameterization scheme and (4) estimation of the roughness length on the sea surface were modified. The schemes (1) to (3) had already been implemented into the Global Spectral Model (GSM) by Kuma et al. (2001). Preliminary experiments with three typhoons in 2002 were carried out for 108 cases. The results showed remarkable improvements in track prediction and neutral skill in intensity prediction of typhoon.
   Text [PDF 0.8MB]

   Development of a Cumulus Parameterization Scheme for the Operational Global Model at JMA
   Masayuki NAKAGAWA
   Numerical Prediction Division, Japan Meteorological Agency
   Akihiko SHIMPO
   Climate Prediction Division, Japan Meteorological Agency

  The Japan Meteorological Agency (JMA) adopted a prognostic Arakawa-Schubert scheme (Arakawa and Schubert 1974; Moorthi and Suarez 1992; Randall and Pan 1993; Pan and Randall 1998) for cumulus parameterization in Global Spectral Model (GSM). JMA revised this scheme in March 2001 to include a reevaporation effect of the convective precipitation (GSM0103) with a view to improving its performance in the medium- to long-range predictions of tropical precipitation and associated circulation. Preliminary forecast experiments indicated that the GSM without the cooling and moistening effects of the reevaporation tended to produce stronger precipitation over the intertropical convergence zone as compared with observation and weaker one in the vicinity of the Philippines. This erroneous precipitation distribution was the main reason for poor medium- to long- range weather prediction of the GSM prior to the implementation of GSM0103. However, GSM0103 had a cold bias and an associated systematic error for geopotential height field in forecast at the lower troposphere over wide areas of the low latitudes especially in the summer hemisphere on early forecast days. The main reason for these errors was the excessive cooling by evaporating convective precipitation. JMA has developed a new cumulus parameterization scheme which considers the detrainment effect in addition to the entrainment between the cloud top and the cloud base in convective downdraft and abolishes reevaporation of convective precipitation (GSM0305). This paper gives results of forecast/assimilation experiments to evaluate two versions of GSM.
   Text [PDF 0.3MB]

   Operational Use of ATOVS Radiances in Global Data Assimilation at JMA
   Masahiro KAZUMORI, Kozo OKAMOTO and Hiromi OWADA
   Numerical Prediction Division, Japan Meteorological Agency

  The Advanced TIROS Operational Vertical Sounder (ATOVS) radiances have been operationally assimilated in the Japan Meteorological Agency (JMA) global 3D-Var data assimilation system since 28 May 2003. It replaced TOVS/ATOVS retrievals, which had been assimilated in the JMA global data assimilation system. The direct assimilation of ATOVS radiances is superior to its retrieval assimilation because the retrievals have some error in their conversion from radiance to analysis variables such as temperature and relative humidity. Data assimilation experiments, which was conducted before the operational use of ATOVS radiances demonstrated significant impacts on forecasts and analyses. This report describes the ATOVS data used at JMA and some results of the assimilation experiments.
   Text [PDF 0.4MB]

   Assimilation of QuikSCAT/SeaWinds Ocean Surface Wind Data into the JMA Global Data Assimilation System
   Yasuaki OHHASHI
   Numerical Prediction Division, Japan Meteorological Agency

  A satellite-borne scatterometer obtains the surface wind vectors over the ocean by measuring the radar signal returned from the sea surface. It provides valuable information such as a typhoon center for numerical weather prediction (NWP) over the ocean, where conventional in situ observations are sparse. Observational data from the European Remote-Sensing Satellite 2 (ERS2) /Active Microwave Instrument (AMI) scatterometer launched by the European Space Agency (ESA) was used operationally at the Japan Meteorological Agency (JMA) from July 1998 to January 2001. A new scatterometer named SeaWinds was launched onboard the QuikSCAT satellite by the National Aeronautics and Space Administration (NASA) /Jet Propulsion Laboratory (JPL) on 19 June 1999. It was a “quick recovery” mission to fill the gap created by the loss of data from the NASA Scatterometer (NSCAT), when the Japanese Advanced Earth Observation Satellite (ADEOS) lost power in June 1997. The width of swath of QuikSCAT/SeaWinds is 1800 km, which is wider than that of ERS2/AMI by three times, with a spatial resolution of 25 km. Daily coverage is more than 90% of the global ice-free oceans. This report described a quality control system for SeaWinds data,results from data assimilation experiments, and conclusions and future plans of assimilation of scatterometer data.
   Text [PDF 0.3MB]

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