An Evaluation of the Advanced Dvorak Technique (9.0) for the tropical cyclones over the North Indian Ocean

The Advanced Dvorak Technique(ADT)is used by tropical cyclone prediction centres around the world to accurately evaluate the intensity of tropical cyclones(TCs)from meteorological operational satellites.The algorithm development team has introduced new improvements to the objective ADT to further extend its capabilities and accuracy.A study has therefore undergone to evaluate the new edition of ADT(9.0)based on all the North Indian Ocean Tropical cyclones during 2018,2019 and 2020(Total 15 No.).It is found that ADT(9.0)performed well with the conformity of IMD’s best track T.No estimates.ADT is reasonably good in estimating the intensity for T≥4.0(VSCS to SuCS)and overestimate the intensity for T≤3.5(CS/SCS).

Multi-Factor Intensity Estimation for Tropical Cyclones in the Western North Pacific Based on the Deviation Angle Variance Technique

In this paper, the infrared cloud images from Fengyun series geostationary satellites and the best track data from the China Meteorological Administration(CMA-BST) in 2015–2017 are used to investigate the effects of two multifactor models, generalized linear model(GLM) and long short-term memory(LSTM) model, for tropical cyclone(TC) intensity estimation based on the deviation angle variance(DAV) technique. For comparison, the typical singlefactor Sigmoid function model(SFM) with the map minimum value of DAV is also used to produce TC intensity estimation. Sensitivity experiments regarding the DAV calculation radius and different training data groups are conducted, and the estimation precision and optimum calculation radius for DAV in the western North Pacific(WNP) are analyzed. The results show that the root-mean-square-error(RMSE) of the single-factor SFM is 8.79–13.91 m s^-1 by using the individual years as test sets and the remaining two years as training sets with the optimum calculation radius of 550 km. However, after selecting and using the high-correlation multiple factors from the same test and training data, the RMSEs of GLM and LSTM models decrease to 5.93–8.68 and 4.99–7.00 m s^-1 respectively, with their own optimum calculation radii of 350 and 400 km. All the sensitivity experiments indicate that the SFM results are significantly influenced by the DAV calculation radius and characteristics of the training set data, while the results of multi-factor models appear more stable. Furthermore, the multi-factor models reduce the optimum radius within the process of DAV calculation and improve the precision of TC intensity estimation in the WNP, which can be chosen as an effective approach for TC intensity estimation in marine areas.

APPLICATION OF DVORAK TECHNIQUE DURING THE WEAKENING STAGE OF TROPICAL CYCLONES

The Dvorak technique has been widely used by operational warning centres around the world as a major analysis tool to determine the intensity of a tropical cyclone(TC).However,there exist noticeable differences in the application of the technique among different warning centres.In particular,the weakening rules in the technique that governs the determination of TC intensity during the TC weakening stage constitute one such difference and are the subject of review in this paper.Three options to modify the weakening rules are introduced and evaluated based on verification against the best-track datasets from various centres.

Dvorak技术估测热带气旋强度研究进展

在常规观测资料稀少的热带洋面上,卫星云图是监测热带气旋的主要工具。Dvorak技术通过一系列经验规则,将热带气旋在卫星云图中表现出来的云系结构特征及特定的参数同其发展强度联系起来。介绍了利用Dvorak技术估测热带气旋强度的研究背景和原理方法,总结了国内外在该领域的研究进展及其存在的优势和不足,指出Dvorak技术是目前业务化估测热带气旋强度的主要工具,同时展望了该技术未来的发展方向。

基于TCR模型的台风极值降雨强度预测

近些年台风带来的强降雨与洪水灾害给沿海城市造成严重的经济损失和人员伤亡,极端降雨环境多数是在台风作用下产生的,且极值降雨强度是城市防洪排涝、排水规划和工程设计的雨量计算依据。为更加合理准确地预测极值降雨,文章引入热带气旋降雨(tropical cyclone rainfall,TCR)模型,利用蒙特卡罗(Monte Carlo)技术模拟香港地区的极值降雨强度。对比相关规范与历史数据,该方法能较好地预测极值降雨强度,为后续台风降雨灾害危险性分析和排水工程建设研究提供一定的参考。

气象卫星资料在估测热带气旋强度方向的应用进展

在常规观测资料稀少的热带洋面上,气象卫星是监测热带气旋的主要工具。基于可见光和红外的Dvorak技术通过一系列经验规则,将热带气旋在卫星云图中表现出来的云系结构特征及特定的参数同其发展强度联系起来,但它无法得到气旋内部辐射信息。相对而言,波长较长的微波能穿透热带气旋中高层云系,反映出与热带气旋强度相关的暖核辐射信息。介绍了国内外利用Dvorak技术和星载微波技术估测热带气旋强度的研究进展,指出它们在应用中存在的优势和不足,同时展望了该领域在未来的发展方向。