Marine-Atmospheric Boundary Layer Characteristics over the South China Sea During the Passage of Strong Typhoon Hagupit

The structures and characteristics of the marine-atmospheric boundary layer over the South China Sea during the passage of strong Typhoon Hagupit are analyzed in detail in this paper. The typhoon was generated in the western Pacific Ocean, and it passed across the South China Sea, finally landfalling in the west of Guangdong Province. The shortest distance between the typhoon center and the observation station on Zhizi Island(10 m in height) is 8.5 km. The observation data capture the whole of processes that occurred in the regions of the typhoon eye, two squall regions of the eye wall, and weak wind regions,before and after the typhoon's passage. The results show that:(a) during the strong wind(average velocityˉu 10 m s-1) period, in the atmospheric boundary layer below 110 m, ˉu is almost independent of height,and vertical velocity ˉw is greater than 0, increasing with ˉu and reaching 2–4 m s-1in the squall regions;(b) the turbulent fluctuations(frequency 1/60 Hz) and gusty disturbances(frequency between 1/600 and1/60 Hz) are both strong and anisotropic, but the anisotropy of the turbulent fluctuations is less strong;(c) ˉu can be used as the basic parameter to parameterize all the characteristics of fluctuations; and(d) the vertical flux of horizontal momentum contributed by the average flow(ˉu ·ˉw) is one order of magnitude larger than those contributed by fluctuation fluxes(u w and v w), implying that strong wind may have seriously disturbed the sea surface through drag force and downward transport of eddy momentum and generated large breaking waves, leading to formation of a strongly coupled marine-atmospheric boundary layer. This results in ˉw 0 in the atmosphere, and some portion of the momentum in the sea may be fed back again to the atmosphere due to ˉu ·ˉw 0.     

利用Argo剖面浮标分析上层海洋对台风“布拉万”的响应

In situ observations from Argo profiling floats combined with satellite retrieved SST and rain rate are used to investigate an upper ocean response to Typhoon Bolaven from 20 through 29 August 2012. After the passage of Typhoon Bolaven, the deepening of mixed layer depth(MLD), and the cooling of mixed layer temperature(MLT) were observed. The changes in mixed layer salinity(MLS) showed an equivalent number of increasing and decreasing because the typhoon-induced salinity changes in the mixed layer were influenced by precipitation, evaporation, turbulent mixing and upwelling of thermocline water. The deepening of the MLD and the cooling of the MLT indicated a significant rightward bias, whereas the MLS was freshened to the left side of the typhoon track and increased on the other side. Intensive temperature and salinity profiles observed by Iridium floats make it possible to view response processes in the upper ocean after the passage of a typhoon. The cooling in the near-surface and the warming in the subsurface were observed by two Iridium floats located to the left side of the cyclonic track during the development stage of the storm, beyond the radius of maximum winds relative to the typhoon center. Water salinity increases at the base of the mixed layer and the top of the thermocline were the most obvious change observed by those two floats. On the right side of the track and near the typhoon center when the typhoon was intensified, the significant cooling from sea surface to a depth of 200×104 Pa, with the exception of the water at the top of the thermocline, was observed by the other Iridium float. Owing to the enhanced upwelling near the typhoon center, the water salinity in the near-surface increased noticeably. The heat pumping from the mixed layer into the thermocline induced by downwelling and the upwelling induced by the positive wind stress curl are the main causes for the different temperature and salinity variations on the different sides of the track. It seems that more time is required for the anomalies in the subsurface to be restored to pretyphoon conditions than for the anomalies in the mixed layer.     

Numerical simulation on a tremendous debris flow caused by Typhoon Morakot in the Jiaopu Stream,Taiwan

In August 2009,Typhoon Morakot brought a large amount of rainfall with both high intensity and long duration to a vast area of Taiwan.Unfortunately,this resulted in a catastrophic landslide in Hsiaolin Village,Taiwan.Meanwhile,large amounts of landslides were formed in the Jiaopu Stream watershed near the southeast part of the Hsiaolin Village.The Hsiaolin Village access road（Provincial Highway No.21 and Bridge No.8） was completely destroyed by the landslide and consequent debris flow.The major scope of this study is to apply a debris flow model to simulate the disaster caused by the debris flow that occurred in the Jiaopu Stream during Typhoon Morakot.According to the interviews with local residents,this study applied the destruction time of Bridge No.8 and Chen＇s house to verify the numerical debris flow model.By the spatial rainfall distributions information,the numerical simulations of the debris flow are conducted in two stages.In the first stage（before the landslide-dam failure）,the elevation of the debris flow and the corresponding potential damages toward residential properties were investigated.In the second stage（after the landslidedam failure）,comparisons of simulation results between the longitudinal and cross profiles of the Jiaopu Stream were performed using topographic maps and satellite imagery.In summary,applications of the adopted numerical debris flow model have shown positive impact on supporting better understanding of the occurrence and movement of debris flow processes.     

Regional soil erosion in response to land use and increased typhoon frequency and intensity,Taiwan

Reservoir sedimentation data and sediment yields from Taiwanese rivers show increased soil erosion in response to both 20th century changes in land use and a more recent increase in typhoon frequency and intensity. Decadal variations of up to 5- to 20-fold in suspended-sediment rating curves demonstrate supply-limited transport and correspond to increased sediment delivery from hillslopes due to changes in land use, regional ground shaking during the Chi-Chi earthquake, and post-2000 changes in typhoon frequency and intensity. While accelerated erosion in central Taiwan after the Chi-Chi earthquake has been documented previously, our results show that periods of increased upland erosion also occurred earlier, in response to 20th century changes in land use. Analyses of rainfall records and typhoon frequency for the period 1900–2009 further point to an island-wide increase in erosion rates corresponding to increased typhoon frequency and intensity after 1990.     

Spatiotemporal analysis of vegetation index after typhoons in the mountainous watershed

An extensive land cover change was triggered by a series of typhoons, especially Typhoon Morakot in 2009 in Taiwan. The normalized difference vegetation index (NDVI) series from multiple satellite images were applied to monitor the change processes of land cover. This study applied spatiotemporal analysis tools, including empirical orthogonal functions (EOF), and multiple variograms in analyzing space–time NDVI data, and detected the effects of large chronological disturbances in the characteristics of land cover changes. Spatiotemporal analysis delineated the temporal patterns and spatial variability of NDVI caused by these large typhoons. Results showed that mean of NDVI decreased but spatial variablity of NDVI increased after typhoons in the study area. The EOF can clarify the major component of NDVI variations and identify the core area of the NDVI changes. Various approaches showed consistent results that Typhoon Morakot significantly lowered the NDVI in land cover change process. Furthermore, the spatiotemporal analysis is an effective monitoring tool, which advocates the use of the index for the quantification of land cover change and resilience.     

基于降水极端预报指数的福建台风极端降水预报研究

应用1961—2017年中国气象局热带气旋最佳路径数据集、国家地面气象观测站日降水观测资料和2015年8月—2017年12月欧洲中期天气预报中心(ECMWF)集合预报系统降水极端预报指数(EFI)数据,根据百分位法定义台风影响期间福建省各站点的台风极端降水阈值,采用最小阈值法剔除台风极端降水时EFI箱线图中的异常值,保...     

0604号强热带风暴"碧利斯"结构特征及其暴雨成因分析

利用NCEP再分析资料、FY2C卫星的OLR及红外云图资料,以及地面台站观测资料,对0604号强热带风暴“碧利斯”的结构特征以及对其登陆后深入内陆造成强降水的成因进行了综合分析,研究结果表明:(1)强热带风暴“碧利斯”结构不对称,南部云系发展旺盛,强降水集中在风暴南侧,呈现明显的不对称分布;(2)副热带高压强度偏强,位置偏西,使得热带风暴登陆后向西偏南方向移动,并在移动过程中与南海季风相互作用,激发了中尺度强降水系统的不断发生;(3)充沛的水汽条件,低层辐合,高层辐散,并伴有深厚的较强上升运动,以及有利的地形都是热带风暴长时间维持并产生大范围强降水的有利条件.     

8805号登陆台风特大暴雨的数值模拟

应用中尺度模式ＭＭ４,使用了一种简单的模式台风处理方法,成功地模拟了８８０５号台风登陆前后的演变及其伴随的特五暴雨过程,即对分析的台风中心物理量场进行修正而形成与实况极为一致的初值,以期能更好地模拟台风过程。从模拟结果可以看出,台风降水强度中心基本上是随台风登陆移动而变化的,每一时期的降水中心基本上与台风移动的路径一致或略偏前方,在登陆时的降水最大,这种降水变化与台风上升运动的烛一致的,上升运动越     

"泰利"台风低压大暴雨过程分析和数值模拟试验

利用NECP1o×1o的6h分析资料和常规观测等资料,对2005年9月2～4日“泰利”台风低压引发的大暴雨过程的不同尺度的天气系统进行了分析,并用非静力中尺度数值预报模式MM5v3.7进行了数值模拟。结果表明,这次大暴雨天气是在和强大稳定的大陆副高与西太平洋副高、中纬度西风带低槽及其引导从地面南下的冷空气、台风低压和台风倒槽、中尺度对流系统相互作用下发生发展的;深厚的强上升运动及其释放的大量潜热是大暴雨维持的重要机制;模式比较成功地模拟了发生在大地形迎风坡下的大暴雨,而对发生在庐山这种范围很小且陡峭地形下的特大暴雨,则模拟降水量偏小。     

台风“麦莎”活动期间TTL区域的物质分布特征分析

利用ECMWF逐6 h的ERA-Interim再分析资料,分析了台风"麦莎"的环流场、位势高度场以及涡度场随时间的演变,了解台风的发生发展过程。在此基础上,进一步分析了台风发生发展期间热带对流层顶(TTL,称为热带对流层到经流层的过渡带)区域的云覆盖情况和微量物质(臭氧、云冰、水汽)分布特征,并对其产生的原因进行了初步探究。结果表明:(1)台风活动强盛地区的TTL区域臭氧浓度相对较低。(2)台风活动期间TTL区域云冰和水汽的浓度明显升高,浓度的高值中心处于台风中心附近。(3)台风活动会使其上空TTL区域的云覆盖量增加,在TTL区域上存在一个云量的极值区。(4)台风引起的垂直运动造成了对流层和平流层之间的物质交换,进而对TTL区域的微量物质产生重要影响。