Recent advancements in aircraft and in situ observations of tropical cyclones

Observations of tropical cyclones(TC)from aircraft and in situ platforms provide critical and unique information for analyzing and forecasting TC intensity,structure,track,and their associated hazards.This report,prepared for the tenth International Workshop on Tropical Cyclones(IWTC-10),discusses the data collected around the world in TCs over the past four years since the IWTC-9,improvements to observing techniques,new instruments designed to achieve sustained and targeted atmospheric and oceanic observations,and select research results related to these observations.In the Atlantic and Eastern and Central Pacific basins,changes to operational aircraft reconnaissance are discussed along with several of the research field campaigns that have taken place recently.The changes in the use and impact of these aircraft observations in numerical weather prediction models are also provided along with updates on some of the experimental aircraft instrumentation.Highlights from three field campaigns in the Western Pacific basin are also discussed.Examples of in-situ data collected within recent TCs such as Hurricane Ian(2022),also demonstrate that new,emerging technologies and observation strategies reviewed in this report,definitely have the potential to further improve ocean-atmosphere coupled intensity forecasts.

A CHALLENGE OF THE EXPERIMENT ON TYPHOON INTENSITY CHANGE IN COASTAL AREA

The Experiment on Typhoon Intensity Change in Coastal Area(EXOTICCA) was proposed by the China Meteorological Administration(CMA) and Hong Kong Observatory(HKO) and endorsed by the ESCAP/WMO Typhoon Committee(TC). The major goals and objectives of the EXOTICCA are: 1) to conduct the field campaigns on the intensity and structural characteristics of the target offshore and landfall tropical cyclones by employing integrated and novel observation techniques, and 2) to conduct demonstration research on the utilization of the synergized field observation data with the aim of deepening the understanding of the mechanism of structure and intensity changes, to improve the relevant capability of operational analysis, numerical weather prediction(NWP) models forecast, reliable storm surge and flooding and associated risk assessment. The Organizational structure and implementation schedule etc. are also introduced in this paper.

WMO TYPHOON LANDFALL FORECAST DEMONSTRATION PROJECT(WMO-TLFDP) PROGRESS AND FUTURE PLANS

The "WMO Typhoon Landfall Forecast Demonstration Project(TLFDP)" was started in May 2010 in conjunction with the start of the Shanghai World Expo 2010. The project was successful in terms of assisting the local forecasters in providing an efficient tropical cyclone(TC) forecast service for World Expo 2010, demonstrating the performance of the most up-to-date techniques in TC forecasting, and enhancing the ability of forecasters to effectively use products based on advanced TC forecasting techniques. The first phase was completed in December 2012 and the second phase was completed in December 2015. The third phase(TLFDP-III) started in 2016.During its first(2010-2012) and second(2013-2015) phases, TLFDP collected real-time TC forecast products from 15 Typhoon Forecast Product Providers(TFPPs). The products include deterministic track and intensity forecasts, ensemble track and intensity forecasts, deterministic wind radii forecasts, wind probability forecasts, and gridded model outputs. The products were disseminated through the project's website and the operational website of the Shanghai Typhoon Warning Center.TLFDP has made significant progress in TC forecast verification, including setting up the tools for both realtime and post-season TC forecast verification, developing and integrating several new verification techniques, carrying out a survey on the operational status of TC forecast verification in the western North Pacific region, and contributing to the WMO document "Verification of tropical cyclone forecasts". The post-season forecast verification was reported to the Session of the UNESCAP/WMO Typhoon Committee since 2013. New consensus methods for TC track and intensity forecasts were also proposed either based on Ensemble Prediction Systems(EPSs) products or multiple deterministic NWP model products. Two training workshops on TC forecasting were organized by the TLFDP and held in Shanghai, China, in May 2010 and June 2012, respectively, and seven research fellowship projects were implemented as jointly supported by the UNESCAP/WMO Typhoon Committee, Shanghai Typhoon Institute and Hong Kong Observatory.In its third phase(TLFDP-III, 2016-2018), the project will continue its effort on demonstration and evaluation of the newly developed forecasting techniques for TCs, and developing and documenting advanced guidance for the verification of TC forecasts, with special attention to TC intensity and precipitation.

亚太防台减灾中国主要贡献概述

热带气旋(西北太平洋地区称为台风)位居全球十大自然灾害之首,西北太平洋是台风活动最活跃的区域,生成于此的台风年均约占全球的1/3[1].西北太平洋区域各国和地区饱受台风侵袭,单个台风造成数十亿美元直接经济损失的例子时有发生,因灾情严重而被除名(永久命名)的台风每年都有[2].防台减灾受到亚太地区各国各地政府的共同关注,技术交流和信息共享由来已久.早在1880年,上海徐家汇观象台便通过书信的方式与马尼拉等当时全球54个气象台建立了气象信息交换网络(各台回执收到资料后的明信片),并据此于1895年绘制了首张东亚地区的地面天气图,于1920年完成了西北太平洋620个台风路径图的整编.此外,徐家汇观象台于1884年创立的"风球旗语"台风预警体系,受到国际气象组织(International Meteorological Organization,IMO)认可和推荐,并在东亚沿海地区得到广泛应用(香港天文台自1884年开始使用直到2002年)[3].

PERFORMANCE OF TROPICAL CYCLONE FORECAST IN WESTERN NORTH PACIFIC IN 2015

The operational track and intensity forecast errors of tropical cyclones(TCs) over the western North Pacific in 2015 were evaluated on the basis of RSMC-Tokyo's "best-track" dataset. The results showed that position errors for each official agency were under 80 km, 130 km, 180 km, 260 km and 370 km at 24, 48, 72, 96 and 120 hr lead time. Stepped decreases in the values of each quantile were made at every lead times and have been made by global models from 2010 to 2015, especially for long lead time. The results of the Track Forecast Integral Deviation(TFID) show a clearly decreasing trend for most global models, indicating that the TC forecast tracks became increasingly similar to the observations. In 2015, the intensity forecast skill scores for both global and regional models were almost negative. However, the skill of EPSs' intensity forecasting has made significant progress in the past year.

A simplified index to assess the combined impact of tropical cyclone precipitation and wind on China

Relationships between tropical cyclone(TC)precipitation,wind,and storm damage are analyzed for China based on TCs over the period from 1984 to 2013.The analysis shows that the maximum daily areal precipitation from stations with daily precipitation of ≥50 mm and the sum of wind gusts of ≥13.9 m/s can be used to estimate the main damage caused by TCs,and an index combining the precipitation and wind gust of a TC(IPWT)is defined to assess the severity of the combined impact of precipitation and wind.The correlation coefficient between IPWT and the damage index for affecting TCs is 0.80,which is higher than that for only precipitation or wind.All TCs with precipitation and wind affecting China are divided intofive categories,Category 0 to Category 4,based on IPWT,where higher categories refer to higher combined impacts of precipitation and wind.The combined impact category is closely related to damage category and it can be used to estimate the potential damage category in operational work.There are 87.7%,72.9%,69.8%,and 73.4%of cases that have the same or one category difference between damage category and combined impact category for Categories 1,2,3,and 4,respectively.IPWT and its classification can be used to assess the severity of the TC impact and of combined precipitation and wind conveniently and accurately,and the potential damage caused by TCs.The result will be a good supplementary data for TC intensity,precipitation,wind,and damage.In addition,IPWT can be used as an index to judge the reliability of damage data.Further analysis of the annual frequency of combined precipitation-wind impact categories reveals no significant increasing or decreasing trend in impact over China over the past 30 years.

INTRODUCTION AND APPILICATION OF A NEW COMPREHENSIVE ASSESSMENT INDEX FOR DAMAGE CAUSED BY TROPICAL CYCLONES

Using principal component analysis,a new comprehensive assessment index for damage caused by tropical cyclones in China's Mainland is developed based on data from 1984 to 2008.it is a weighted average of four kinds of damage data:including the deaths and missing,affected crop area,destroyed houses,and rate of direct economic loss.The weighting coefficients are set by principal component analysis.Two indices are derived,which differ in the importance of the deaths and missing in severity assessment according to the sign of the second principal component of damage data.Trends in the damage caused by individual tropical cyclones and in the annual frequencies of the various levels of severity of damage caused by tropical cyclones are analyzed.no clear trend in damage from individual tropical cyclones is found.The annual frequency of tropical cyclones causing heavy and catastrophic damage shows a clear decrease from 1984 to 2008 with no trend in the total number of damaging tropical cyclones.

Improving the Extreme Rainfall Forecast of Typhoon Morakot(2009) by Assimilating Radar Data from Taiwan Island and China's Mainland

This study examined the impact of an improved initial field through assimilating ground-based radar data from China's Mainland and Taiwan Island to simulate the long-lasting and extreme rainfall caused by Morakot（2009）. The vortex location and the subsequent track analyzed through the radial velocity data assimilation（VDA） are generally consistent with the best track. The initial humidity within the radar detecting region and Morakot＇s northward translation speed can be significantly improved by the radar reflectivity data assimilation（ZDA）. As a result, the heavy rainfall on both sides of Taiwan Strait can be reproduced with the joint application of VDA and ZDA. Based on sensitivity experiments, it was found that, without ZDA, the simulated storm underwent an unrealistic inward contraction after 12-h integration, due to underestimation of humidity in the global reanalysis, leading to underestimation of rainfall amount and coverage. Without the vortex relocation via VDA, the moister（drier） initial field with（without） ZDA will produce a more southward（northward） track, so that the rainfall location on both sides of Taiwan Strait will be affected. It was further found that the improvement in the humidity field of Morakot is mainly due to assimilation of high-value reflectivity（strong convection） observed by the radars in Taiwan Island, especially at Kenting station. By analysis of parcel trajectories and calculation of water vapor flux divergence, it was also found that the improved typhoon circulation through assimilating radar data can draw more water vapor from the environment during the subsequent simulation, eventually contributing to the extreme rainfall on both sides of Taiwan Strait.

OVERVIEW ON THE PROGRESS OF WORKING GROUP ON METEOROLOGY OF ESCAP/WMO TYPHOON COMMITTEE IN THE RECENT 10 YEARS

This paper reviews the major achievements of the Working Group on Meteorology(WGM) of ESCAP/WMO Typhoon Committee since its establishment in 2004, especially in tropical cyclone observational research and scientific experiments, tropical cyclone monitoring and forecasting technologies, seasonal prediction and climate change assessment for the past decade. The progress illustrates the great value of the Committee and WGM in monitoring and forecasting of tropical cyclones in the region and the improvement of disaster prevention and reduction capabilities.

A METHODOLOGICAL STUDY ON AMH COPULA-BASED JOINT EXCEEDANCE PROBABILITIES AND APPLICATIONS FOR ASSESSING TROPICAL CYCLONE IMPACTS AND DISASTER RISKS(PART Ⅰ)

A disaster induced by a tropical cyclone(TC)is a complex non-linear process,involving interactions of multiple factors.Assuming that the resilience to TC disasters remains basically unchanged,the disaster-causing risk is usually consistent with intensities of the TC-induced rainstorms and wind.When an area is hit by a low probability TC,the rainstorm and wind intensities are higher,and the likelihood for causing a disaster is greater.Therefore,criteria for the impact of a TC and disaster risk assessments can be established based on the probable intensities of the TC-associated rainstorms and wind.In this study,an AMH Copula-based function is introduced to investigate the joint risk probabilities of TC rainstorms and wind.In line with the equivalence principle of the distribution of a stochastic atmospheric phenomenon in both time and space,and taking the impact on Shanghai of TC Haikui as an example,the Copula-based joint probability distribution model is developed to assess the impacts of TC rainstorms and wind,based on the marginal distributions of the maximum daily rainfall and extreme gust velocity.The joint exceedance probabilities of TC rainstorms and wind derived from the model can be used as criteria to measure the risk levels.As our findings show,this approach captures the TC risks well,especially in high-risk areas.The aim of the study is to provide a practically useful concept for making more accurate assessments of the risk level of an extreme weather event using observational data,and objective criteria for risk avoidance and transfer.

Overview of the development history of China’s typhoon research and operational work in the past century

Because typhoons are one of the most major natural disasters in the southeastern coastal areas of China,great attention has been paid to the prevention and mitigation of the disasters caused by typhoons.Over the past century,significant progress has been made in typhoon-related scientific research and operational work in China,including the construction of a network of typhoon monitoring stations,the establishment of forecasting operation systems,early warning and prevention of typhoon-related disasters,and the research of basic theories of typhoon behaviors and key forecasting technologies.This paper briefly reviews the milestones in the development history of typhoon research in China over the past century and a half in order to commemorate the predecessors,especially those who made historical contributions to the advancement of typhoon research since the economic and cultural reforms known as the"Opening of China",who provided historical references which enabled China to become an international leader in the field of typhoon science and technology.