Observed and projected climate change in Taiwan

Summary This study examined the secular climate change characteristics in Taiwan over the past 100 years and the relationship with the global climate change. Estimates for the likelihood of future climate changes in Taiwan were made based on the projection from the IPCC climate models. In the past 100 years, Taiwan experienced an island-wide warming trend (1.0–1.4 °C/100 years). Both the annual and daily temperature ranges have also increased. The warming in Taiwan is closely connected to a large-scale circulation and SAT fluctuations, such as the “cool ocean warm land” phenomenon. The water vapor pressure has increased significantly and could have resulted in a larger temperature increase in summer. The probability for the occurrence of high temperatures has increased and the result suggests that both the mean and variance in the SAT in Taiwan have changed significantly since the beginning of the 20th century. Although, as a whole, the precipitation in Taiwan has shown a tendency to increase in northern Taiwan and to decrease in southern Taiwan in the past 100 years, it exhibits a more complicated spatial pattern. The changes occur mainly in either the dry or rainy season and result in an enhanced seasonal cycle. The changes in temperature and precipitation are consistent with the weakening of the East Asian monsoon. Under consideration of both the warming effect from greenhouse gases and the cooling effect from aerosols, all projections from climate models indicated a warmer climate near Taiwan in the future. The projected increase in the area-mean temperature near Taiwan ranged from 0.9–2.7 °C relative to the 1961–1990 averaged temperature, when the CO₂ concentration increased to 1.9 times the 1961–1990 level. These simulated temperature increases were statistically significant and can be attributed to the radiative forcing associated with the increased concentration of greenhouse gases and aerosols. The projected changes in precipitation were within the range of natural variability for all five models. There is no evidence supporting the possibility of precipitation changes near Taiwan based on the simulations from five IPCC climate models. Received February 5, 2001 Revised July 30, 2001     

MODIS遥感数据在我国台湾海峡海雾监测中的应用

海雾是一种常见的灾害性天气现象。以我国台湾海峡为示范研究区, 利用新一代卫星传感器MODIS的可见光和红外探测通道数据, 在分析海洋、中高云、低云和海雾等不同下垫面的MODIS光谱辐射特征基础上, 选择对海雾具有敏感反应的探测通道, 通过综合判识建立台湾海峡海雾遥感监测模型。利用该模型对2004-2007年我国台湾海峡海雾事件进行监测, 并用福建沿海5个地面气象观测站的能见度数据对监测结果进行验证分析。结果表明:基于MODIS数据的海雾遥感监测模型能够较准确地对台湾海峡海雾分布和发展过程进行监测, 从地面观测数据与卫星监测结果对比验证来看, 海雾监测的准确率可达80 %以上, 具有较高的业务化应用前景。     

台湾海峡西岸海雾研究现状与未来发展方向

台湾海峡是一个海雾多发的交通要道,海雾灾害往往会导致人员和财产损失。对当前有关的海雾研究现状进行总结,以海峡西岸为代表,比较台湾海峡海雾和其他海域的大雾研究进展状况,主要包括海雾发生时的天气气候学特征、监测手段、微物理特征研究和海雾数值预报研究等。结果表明,台湾海峡西岸在天气气候学方面已经取得了一定的成果;监测手段随着科学技术的发展,也不断的完善,但在如何对卫星遥感监测结果进行反演方面还需进一步研究;海雾的微物理特征研究有助于海雾模式的改进和卫星遥感海雾反演技术的提高,但台湾海峡西岸尚未开始研究,是下一步的研究重点;台湾海峡海雾数值模拟工作较少,伴随观测技术的不断进步、动力统计方法的不断完善,可通过数值预报产品与传统的天气学方法相结合,提高台湾海峡海雾预报水平。     

A Numerical Study of Precipitation Characteristics over Taiwan Island during the Winter Season

Summary  Two-thirds of the land mass of Taiwan island is mountainous, which affects the airflow and precipitation systems over the island. In this study, we discuss the characteristics of precipitation systems when the prevailing wind direction is from the north-east during winter. Observations indicate that rainfall amounts were higher in northeastern Taiwan (the upstream side of the mountains) and that a rainfall shadow occurred in southwestern Taiwan. Simulation results from a non-hydrostatic model indicate that airflow was deflected in eastern Taiwan, while relatively high (low) pressure areas formed in eastern (western) Taiwan. A higher mixing ratio of rainfall occurred over northeastern Taiwan while lighter rainfall occurred in the eastern, and northwestern areas and the southern tip of Taiwan. This was consistent with the observational data except for the southern tip of Taiwan. Uplift due to the topography near the mountainous areas, as well as low level convergence near the coastal areas (due to the deceleration of an easterly wind in northeastern Taiwan), helped form the mixing ratio of rain. Transportation of the mixing ratio of rainfall, due to low level westward flow and upper level eastward flow, caused it to cover a larger area. The mixing ratio of rainfall formed in the upper mountainous areas in northeastern Taiwan if the upstream moisture content was reduced significantly. A temperature inversion at low levels resulted in a decrease in relative humidity and an increase in stability, requiring that the mixing ratio of rainfall should develop closer to the mountainous areas. If a low level wind blew parallel to the orientation of the mountains (NNE-SSW), a higher mixing ratio of rainfall could occur in the mountainous areas of western Taiwan. Received January 30, 1998 Revised February 19, 1999     

A NUMERICAL STUDY OF THE EFFECT OF TAIWAN ISLAND TERRAIN ON TYPHOON HAITANG （0505） TRACK

The track of Typhoon Haitang (0505), which passed through the Taiwan Island and landed again,has been successfully simulated by using the non-hydrostatic mesoscale atmospheric model MM5. Itsstructure is analyzed on the landing stage, and it is found that there exist good relationships between thetyphoon abnormal moving track and its asymmetry structure. The effect of terrain of Taiwan Island on thetyphoon Haitang, which made it rotate before landing and present a "V" type abnormal moving track inTaiwan straits, has also been simulated. Further analysis shows that the terrain of Taiwan Island not onlydirectly affects the typhoon moving track, but also changes the typhoon track by affecting its asymmetricstructure. Therefore, the typhoon asymmetric structure and the effect of terrain of Taiwan Island togetherresults in the abnormal rotating track. The terrain of Taiwan Island tends to increase the SW-NEasymmetric structure of the typhoon and has different effect on SE-NW asymmetric structure during thelandfall process of typhoon Haitang before entering and moving out of the Taiwan straits.     

近10年台湾海峡海面风场的时空特征变化动态分析

利用台湾海峡ASCAT海面风场数据和气象观测资料,通过EOF和统计方法综合分析台湾海峡海面风场2007—2017年10年的时空模态变化特征,使用Mann-Kendall法和滑动t-检验法对10年间海面风速进行突变检验,对台湾海峡海面风场季节变化时空特征进行分析研究。(1) “狭管效应”在台湾海峡海面风场上呈现明显的季节性特征,其中春季、秋季和冬季海面风场季节性特征显著,夏季表现不明显。受台湾岛地形和季风环流影响,台湾岛南北两端海面易出现风速增强的角流区,岛中央山脉背风区易出现低风速尾流区。(2) 10年间台湾海峡海面月平均风场EOF空间模态受台湾岛地形影响显著,台湾海峡海域为异常值偏差中心,易发生风速突然增幅和风向改变。时间模态大体表现为季节性振荡型变化,振幅在10年中表现为不活跃,呈逐年递减趋势。(3) Mann-Kendall法和滑动t-检验法等方法的突变检验结果表明风速并未发生显著性突变,10年间台湾海峡海面风速特征表现为从正相位向负相位的改变,且随着趋势持续加大,将可能发生风速突变。      

台湾岛地形诱生次级环流系统对热带气旋异常运动的影响机制

对经过中国台湾岛和海南岛、吕宋岛、日本诸岛以及朝鲜半岛的热带气旋在过岛前后的运动、结构和强度的时空变化进行了统计诊断分析。研究结果表明,台湾岛附近热带气旋运动左偏（定义为偏于以前路径的左侧）机率最大,且台湾岛周围是产生诱生低压的高频区。采用理想东、西风环境场作为数值模拟背景场,数值研究了岛屿地形强迫与台湾附近的环境流场的相互作用及其对热带气旋运动偏转的影响,提出了岛屿地形强迫、背景场和热带气旋涡旋三者相互作用对热带气旋路径突然转折影响的观点,即台湾地形有利于环境场中诱生出一对偏差偶极涡,这对诱生偏差偶极涡将导致逼近岛屿的热带气旋产生运动方向的突然偏折,且在不同基本气流条件下,岛屿地形对热带气旋运动可能产生显著不同的影响。     

台湾岛地形对台风“海棠”(0505)移动路径影响的数值试验研究

利用非静力模式MM5模拟台风“海棠”（0505）穿过台湾岛再次登陆的移动路径，分析了“海棠”登陆台湾岛前后结构特征变化。结果表明：台风自身的非对称结构与台风异常移动路径密切相关。另外，就台湾岛地形对台风“海棠”登陆台湾前打转和在台湾海峡出现“V”型移动异常路径影响进行数值试验表明：台湾岛地形不但可以直接影响台风移动路径，而且通过影响台风非对称结构来改变台风移动路径，因此，登陆台湾前逆时针打转异常路径是在弱引导气流中台风自身非对称结构和台湾岛地形共同作用的结果；台湾岛地形有使台风东北-西南向非对称增大趋势，而在台风进入台湾海峡前后对东南。西北向非对称有明显不同影响。     

A numerical case study of the passage of a cold surge across Taiwan

Summary A numerical study of a cold surge that occurred from 19–23 December 2001 was conducted to better understand the cold surge characteristics over the Taiwan area. The National Centers for Environmental Prediction (NCEP) nested Mesoscale Spectral Model (MSM) was used for this study. Simulation results demonstrated that the nested NCEP MSM captured salient features of the selected cold surge case. We demonstrated that the local minimum center of the time change of virtual potential temperature (dVPT) can serve as the location of severe weather of the cold surge for all Taiwan regions. Furthermore, thermodynamic equation analyses revealed that the leading edge of the cold surge was maintained primarily by meridian thermal advection, while diabatic heating, vertical and zonal thermal advections were less important. The cold surge flows were blocked and lifted by the Central Mountain Range (CMR) on its windward side, which increased the cold surge’s vertical extent upward and increased northwestward tilting in the vertical structure. The flow eventually ascended, switched direction toward Taiwan, and descended over its northwestern and eastern coasts. The physical and circulatory characteristics of the cold surge differed noticeably on both sides of Taiwan. The cold surge’s leading edge over the Taiwan Strait was northeast-southwest oriented and had evident wind shear; on the east side of the island, it was stronger in intensity and faster-moving than its counterpart on the west side. Sensitivity experiments revealed that the CMR’s trapping of cold surge flows on its windward side affected cold surge leading edge characteristics in the following five ways: (1) weakening its intensity over the ocean but enhancing it inland, (2) decreasing its southward speed, especially over the western low plains region, but increasing its movement on the east coast, (3) increasing its vertical altitude and narrowing the horizontal extent of its vertical tilting, (4) altering its upper vertical circulatory structure, and (5) trapping a V-shape density current and enhancing its intensity in connection with the land-sea contrast.     

台湾岛及邻近区域热带气旋异常路径特征分析

利用热带气旋资料和天气图、卫星云图等观测资料,统计分析了1949-2008年入侵台湾岛及邻近区域的热带气旋出现的各类异常路径的时间、空间分布规律及成因。结果表明,异常路径的形成是环境流场和台湾地形共同作用的结果,在特定的环流形势下,台湾地形的影响,导致入侵这一带区域的热带气旋结构及其周围的气压场和流场发生变化,并可能诱生出地形槽或低压。热带气旋出现左折、右折、打转和诱生低压发展取代原热带气旋的异常路径,发生在不同地点的异常路径,地形和环境作用的主次关系不同。