Initialization and Simulation of a Typhoon Using 4-Dimensional Variational Data Assimilation-Research on Typhoon Herb(1996)

The MM5 and its four dimensional variational data assimilation (4D-Var) system are used in thispaper. Based on the National Centers for Environmental Prediction/National Center for AtmosphericResearch (NCEP/NCAR) reanalysis data, the authors generate an optimal initial condition for a typhoonby using the bogus data assimilation (BDA) scheme. BDA is able to recover many of the structuralfeatures of typhoons including a warm-core vertex, the correct center position, and the strong circulation.As a result of BDA using a bogus surface low, dramatic improvement is achieved in the 72 h predictionof typhoon Herb. Through several cases, the initialization by BDA effectively generates the harmoniousinner structure of the typhoon, but which is lacking in the original analysis field. Therefore the intensityforecast is improved greatly. Some improvements are made in the track forecast, but more work still needsto be done.