Reconstruct the Mesoscale Information of Typhoon with BDA Method Combined with AMSU-A Data Assimilation Method

Yunfeng Wang,Xiaoping Cheng,Yueqi Han,Haiyang Zhang,Bin Wang

doi:10.1155/2010/346516

Abstract

This paper conducts the assimilating experiments and simulating experiments on typhoon “Aere” (No. 0418), by use of bogus data assimilation (BDA) method combined with advanced microwave sounding unit-A (AMSU-A) data assimilation method in the fifth-generation National Center for Atmospheric Research (NCAR)/Penn State Mesoscale Model Version-3 (MM5V3), the Radiative Transfer for TIROS-N Operational Vertical Sounder Version-7 (RTTOV) model, and their adjoint models. The Bogus data constructed with BDA technique are mainly located at sea level, while the peak energy contribution levels of the sounder channels selected in AMSU-A data assimilation technique are mainly located at upper troposphere. The two types of data can reconstruct the meso-scale information and improve the typhoon initial fields under the model dynamic forcing effect, respectively from the low level and the upper level of atmosphere during the assimilating process. Numerical results show that with four-dimensional variational data assimilation (4DVAR) technique the circulation of initial fields is improved, the “warm core” of typhoon is enhanced, the “cloud water” phenomenon that occurs in the optimal initial fields and the numerical model is changed into “warm start” from “cold start”.

Highlights

Typhoon is one of the most frequent disasters affecting human beings
Initial fields of model Provided by National Centers for Environmental Prediction (NCEP) data Provided by bogus data assimilation (BDA) method Provided by BDA method combined with advanced microwave sounding unit-A (AMSU-A) data assimilation method of Luzon, Philippines on August 20, 2004, and it moved west-northward under the lead of the subtropical high, with maximum wind speed of up to 43 m/s
Though the BDA method is not very effective in improving the initial typhoon circulation fields at high level, it is more effective in decreasing sea level pressure of initial typhoon

Summary

Introduction

Typhoon is one of the most frequent disasters affecting human beings. With the development of numerical forecasting techniques, numerical forecasting of typhoon has entered an operational stage. Zhang et al [18] adopted 3-dimensional variational assimilation (3DVAR) technique to assimilate AMSU brightness temperature data into numerical model in the study of the typhoon structure and its evolution in different stages on Northwest Pacific. Where the superscript “T” denotes transpose, B is the error covariance matrix of background fields, P(r) and V (r) are, respectively, sea level pressure and sea level wind of model atmosphere, WP and WV are the corresponding weighting coefficients, “ ” denotes the sum, the subscript sign “t” denotes different observing times, the subscript sign “i” denotes different spatial observing positions at the same time, HBTA denotes the observed operator of calculating the simulated brightness temperature with model atmospheric variables, BTA denotes the actual AMSU-A observation data, and WBTA denotes the weighting coefficient of detective channels. They are, respectively, 10.41, 9.24, 12.54, and 11.90

Numerical Experiments

Numerical Results

Conclusions