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A New Variational Assimilation Method for Numerical Typhoon Simulation Based on Gradient Information of Satellite Data

ZHONG Bo;WANG Yunfeng;MA Gang;MA Xinyuan

Chinese Journal of Atmospheric Sciences,Vol 42,No. 01

【Abstract】 Satellite data have been widely used as a non-conventional meteorological data in numerical weather prediction due to its global coverage and continuous, high-frequency observations. However, there are a variety of observation errors in satellite observations, including the random errors caused by the contingency of observations and systematic errors brought by the instrument itself and introduced by the community radiative transfer model, which influence the quality of satellite data to a large extent. A method of gradient information assimilation to correct the systematic errors of satellite data is proposed in this paper, which uses a gradient operator to make gradient transformation between the model variables and observation variables and realize the objective to eliminate the systematic errors. A numerical simulation of typhoon Kompasu is then conducted using the weather research forecast (WRF) and WRF data assimilation system (WRFDA) model as well as the atmospheric infrared sounder (AIRS) data. The results indicate that the method of gradient information assimilation can greatly improve the simulation of Kompasu’s track, and the method can also be applied to process data with low reliability. In addition, through the assimilation diagnosis analysis, it is found that the systematic error of the satellite data has a great impact on numerical simulation of typhoons, and the gradient information assimilation method proposed in this paper can solve this kind of problem.

A Mechanism Study on the Sudden Track Change of Super Typhoon Goni (2015)

BI Xinxin;CHEN Guanghua;ZHOU Weican

Chinese Journal of Atmospheric Sciences,Vol 42,No. 01

【Abstract】 Based on the best track data from China Meteorological Agency and 6-h reanalysis data with a resolution of 1° × 1° from National Centers for Environmental Prediction, this study conducts the piecewise potential vorticity inversion to reveal the dynamic mechanism by which the 15th super typhoon Goni in 2015 suddenly changed its track. The results are as follows. (1) From the perspective of synoptic system, Goni was affected by the large-scale background system and the steering flows including the Northwest Pacific subtropical high, the monsoon gyre, the typhoon Atsani and the peripheral anticyclone of Atsani during the whole lifetime of Goni. (2) On the basis of quantitative analysis of the steering flow inverted from potential vorticity perturbation associated with the four components, we find that the steering flow vector of Goni was always affected by the Northwest Pacific subtropical high, while the monsoon gyre and peripheral anticyclone played a secondary role. At the time when Goni turned northward suddenly, the steering flow associated with the peripheral anticyclone acted as a major factor that resulted in the abrupt northward turning. (3) The contribution of the total potential vorticity perturbation to the relevant steering flow at different altitudes is further analyzed quantitatively. Results show that the steering flow vector in the middle troposphere is in good agreement with the movement of Goni, and the southerly flow formed in the low-level system is closely related to Goni’s abrupt northward turning and its subsequent enhancement in the upper troposphere after the abrupt turning.

Application of Potential Vorticity Tendency in Track Recurvature Study of Typhoon Muifa

YUAN Min;PING Fan;LI Guoping

Chinese Journal of Atmospheric Sciences,Vol 42,No. 02

【Abstract】 Horizontal advection and diabatic heating terms in the potential vorticity tendency equation are used to diagnose the twice track changes of typhoon Muifa based on ECMWF data. The results show that horizontal advection is about one order of magnitude larger than diabatic heating; large-scale steering flows represented by horizontal advection mainly contributed to the first track change; horizontal advection and diabatic heating both contributed to the second track change, while horizontal advection controlled the direction and diabatic heating restrained its track recurvature.

Diagnostic study and numerical simulation on the structure of Typhoon “Muifa” during its two recurving processes

YUAN Min;PING Fan;LI Guoping

Chinese Journal of Atmospheric Sciences,Vol 42,No. 05

【Abstract】 A variety of data are used to analyze and study the two recurving processes of typhoon “Muifa”. The results show that changes in the northwestern pacific subtropical high, the mid-latitude trough and cross-equatorial flows all have impacts on the two recurving processes of “Muifa”. The internal TC structure such as the spiral cloud bands and eye wall changed little during the first recurving but they experienced huge changes during the second recurving with the formation of asymmetric structure, the replacement of eye wall and the merging of spiral cloud bands with eye wall. Numerical studies confirmed the above changes during the second recurving process. The mechanism study shows that the zonal and meridional components of environmental flow accounted for more than 83% of the steering flow for the first recurvature. For the second recurvature, the zonal component of storm-scale flow accounted for 23%–36%, while its meridional component accounted for 35%–47% of the steering flow.

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