A GCM-Based Forecasting Model for the Landfall of Tropical Cyclones in China

A statistical dynamic model for forecasting Chinese landfall of tropical cyclones (CLTCs) was developed based on the empirical relationship between the observed CLTC variability and the hindcast atmospheric circulations from the Pusan National University coupled general circulation model (PNU-CGCM).In the last 31 years,CLTCs have shown strong year-to-year variability,with a maximum frequency in 1994 and a minimum frequency in 1987.Such features were well forecasted by the model.A cross-validation test showed that the correlation between the observed index and the forecasted CLTC index was high,with a coefficient of 0.71.The relative error percentage (16.3%) and root-mean-square error (1.07) were low.Therefore the coupled model performs well in terms of forecasting CLTCs;the model has potential for dynamic forecasting of landfall of tropical cyclones.     

影响我国的热带气旋年频数预测

利用中国气象局《热带气旋年鉴》的热带气旋大风和降水资料集,确定了明显影响我国及华东和华南地区的热带气旋个例,并研制热带气旋年频数的预测方案,使得频数预测对防灾减灾更为实用。预测因子采用相关普查的方法,从1961—2000年前期的海表温度、海平面气压及200,500 hPa和850 hPa位势高度和风场中选出,所用的资料为NOAA ER SST和NCEP/NCAR再分析资料。在相关分析的基础上,构建因子时兼顾了因子的系统性的空间结构和时间的变化,并用主成分分析方法去除因子的多重共线性;在最优子集回归建模的基础上进一步对模型进行检验和优化。模型检验和2001—2008年回报试验说明各模型均对各自热带气旋频数 (TCF) 具有较好的预测能力。     

Variation of the monsoon trough intensity in the South China Sea and western North Pacific ocean and its relationship to tropical cyclone activities

Using the daily average of the NCEP/DOE AMIP-II reanalysis data from 1979 to 2005 and the characteristics of monsoon troughs in the western North Pacific,we established an intensity index and a location index to describe the activity of the monsoon troughs in three different regions and their impacts on tropical cyclones generated therein(MTTCs).The behavior of the monsoon troughs was analyzed.The following conclusions are obtained:(1)The established monsoon trough intensity index has a positive correlation to the location index,indicating that stronger monsoon trough intensity corresponds to more northward location.(2)Monsoon trough intensity exhibits significant interannual variation,with obvious periods of 4–5 years prior to 1994 and 2–3 years afterwards.(3)The affecting factors on monsoon trough intensity are different with areas.The preceding SST anomaly results in anomalous atmospheric circulation, leading to the anomaly of monsoon trough intensity in different areas.(4)The frequency of cyclogenesis and location anomalies of the MTTC are closely related to the intensity and location of the monsoon trough. Most of the anomalously less MTTC years coincide with the years with a weak general monsoon trough and weak regional monsoon troughs.The anomalously more MTTC years are associated with both a strong general monsoon trough and a weak general monsoon trough combined with a strong one over the South China Sea,though with a larger probability for the latter.(5)The interseasonal variation of the intensity of monsoon troughs provides favorable conditions for TC generation and development.The monsoon trough is in the active periods of both quasi-biweekly 10 to 20 day and 30 to 60 day oscillations,which is favorable for MTTC occurrence.     

基于TRMM降水数据的山区降水垂直分布特征

选择天山和祁连山区为典型区,利用台站降水数据验证以上两区多卫星降水数据(TRMM)精度的基础上,借助TRMM数据分析了所选山区年降水梯度效应,并探讨了天山及祁连山最大降水高度带.结果表明,多卫星降水数据在天山和祁连山区精度较高,天山及祁连山年降水量都明显受到海拔影响,降水随海拔升高而增加,但天山降水与海拔正相关关系最好,南、北和西坡相关系数分别为0.90、0.81和0.58,多年平均降水直减率分别为11.0mm/100 m、6.3 mm/100 m、7.4 mm/100 m,最大降水高度带则分别位于海拔2 200~3 500 m和3 200~3 700 m和3 000m左右;祁连山东、中、西段降水随海拔有增加趋势,但降水梯度效应在祁连山东段明显高于祁连山中西段地区,梯度效应由东向西呈现递减趋势,其最大降水带主要分布在东段4 000~4 500 m的高山带.     

Ontogenetic habitat use by mangrove/seagrass-associated coral reef fishes shows flexibility in time and space

Tropical shallow-water habitats such as mangroves and seagrass beds are widely acknowledged as important juvenile habitats for various coral reef fish species, most of which are commercially important to fisheries. Spatio-temporal variability in ontogenetic habitat use by fish among these tropical coastal ecosystems has rarely been investigated, yet there are sufficient reasons to believe that this plays an important role. In the present study, we test the spatio-temporal variability in patterns of ontogenetic habitat use by some mangrove/seagrass-associated coral reef fishes (Lethrinus harak, Lethrinus lentjan, Lutjanus fulviflamma and Siganus sutor). Abundances of these four species were investigated during two years in Tanzanian coastal waters, using underwater visual census in mangrove, seagrass, shallow and deep mudflat, and shallow and deep coral reef habitats. The study covered four distinct seasons of the year and was done at two spatially separated (>40 km) locations. Averaged across locations, seasons and years, juveniles (≤10 cm length) of the four study species had significantly higher relative densities in shallow-water (mangroves and seagrass beds) than in deep-water habitats (deep mudflats or coral reefs), whereas the opposite pattern was found for the adults (>15 cm). These findings suggest a strong and general pattern of ontogenetic habitat shifts from shallow- to deep-water habitats. However, specific habitat-use patterns of juveniles as well as adults differed significantly in time and space. Various species showed subtle to considerable flexibility in juvenile as well as adult habitat use across seasons, years, or at different locations. Furthermore, for some species the data suggest presence of ontogenetic habitat shifts at one location but lack thereof at the other location. In summary, ontogenetic habitat use needs to be considered at various spatial and temporal scales for the interpretation of habitat utilization by fish during different life stages. This is important for conservation and management of these habitats, as essential habitats or seasons may be ignored or over-emphasized with respect to their importance for fish during different parts of their life cycle.     

Establishment of an Objective Standard for the Definition of Binary Tropical Cyclones in the Western North Pacific

To develop an objective standard for defining binary tropical cyclones (BTCs) in the western North Pacific (WNP), two best-track datasets, from the China Meteorological Administration and the Joint Typhoon Warning Center, were adopted for statistical analyses on two important characteristics of BTCs—two TCs approaching each other, and counterclockwise spinning. Based on the high consistency between the two datasets, we established an objective standard, which includes a main standard for defining BTCs and a secondary standard for identifying typical/atypical BTCs. The main standard includes two requirements: two coexisting TCs are a pair of BTCs if (i) the separation distance is ≤ 1800 km, and (ii) this separation maintains for at least 12 h. Meanwhile, the secondary standard defines a typical BTC as one for which there is at least one observation when the two TCs approach each other and spin counterclockwise simultaneously. Under the standard, the ratio of typical BTCs increases as the BTC duration increases or the minimum distance between the two TCs decreases. Then, using the JTWC dataset, it was found that there are 505 pairs of BTCs during the period 1951?2014, including 328 typical BTCs and 177 atypical BTCs, accounting for 65.0% and 35.0% of the total, respectively. In addition, a study of two extreme phenomena—the maximum approaching speed and the maximum counterclockwise angular velocity in typical BTCs—shows that the configuration of the circulation conditions and the distribution of the BTCs favor the formation of these extreme phenomena.     

Uncertainty in Tropical Cyclone Intensity Predictions due to Uncertainty in Initial Conditions

Focusing on the role of initial condition uncertainty,we use WRF initial perturbation ensemble forecasts to investigate the uncertainty in intensity forecasts of Tropical Cyclone(TC)Rammasun(1409),which is the strongest TC to have made landfall in China during the past 50 years.Forecast results indicate that initial condition uncertainty leads to TC forecast uncertainty,particularly for TC intensity.This uncertainty increases with forecast time,with a more rapid and significant increase after 24 h.The predicted TC develops slowly before 24 h,and at this stage the TC in the member forecasting the strongest final TC is not the strongest among all members.However,after 24 h,the TC in this member strengthens much more than that the TC in other members.The variations in convective instability,precipitation,surface upward heat flux,and surface upward water vapor flux show similar characteristics to the variation in TC intensity,and there is a strong correlation between TC intensity and both the surface upward heat flux and the surface upward water vapor flux.The initial condition differences that result in the maximum intensity difference are smaller than the errors in the analysis system.Differences in initial humidity,and to a lesser extent initial temperature differences,at the surface and at lower heights are the key factors leading to differences in the forecasted TC intensity.These differences in initial humidity and temperature relate to both the overall values and distribution of these parameters.     

台风“玲玲”对黑龙江暴雨影响分析

选取2019年9月7-8日NCEP/NCAR(1°×1°)再分析资料,分析了降水实况、卫星云图、环流形势、物理量场。结果表明:此次暴雨过程主要受台风登陆后减弱的热带风暴影响,副热带高压的维持为水汽的输送与台风的北进起到了促进作用,台风外围水汽成为此次降水的主要水汽来源,高低空急流耦合加强了动力条件,暴雨落区与高空急流的右侧、低空急流的左侧、垂直运动强上升区及水汽通量散度辐合区有较高的吻合度。     

2019年冬季海洋天气评述

2019年冬季（2019年12月—2020年2月）大气环流特征为：北半球的极涡呈偶极型分布,中高纬呈3波型分布,西风带槽脊较常年明显偏弱。位势高度距平场显示,东亚中纬度地区处于正距平区,东亚大槽强度弱,冷空气强度较常年同期偏弱,大风过程显著偏少,我国近海共出现7次明显的8级以上大风过程,冷空气和温带气旋共同影响的大风过程有2次,冷空气与热带气旋共同影响的大风过程有2次。浪高在2 m 以上的海浪过程有10次。近海出现大范围的海雾过程12次,海雾区域主要出现在渤海、渤海海峡、黄海北部和中部海域、琼州海峡及北部湾,出雾时段多集中于夜间至早晨。海面温度随时间逐渐降低,其从北到南的温度差在冬季由22 ℃加大到27 ℃。西北太平洋和南海共有1个台风生成。     

CWRF边界层参数化对东亚近海热带气旋模拟的影响评估

基于CWRF模式结果,探讨了6种边界层参数化方案对30 a东亚近海热带气旋的强度、频数及路径模拟的可能影响。结果发现：CWRF模式中各边界层参数化方案模拟的热带气旋频数普遍较观测偏少,模拟强度相比观测也均偏弱。热带气旋的强度、频数及出现频次的空间分布对模式边界层方案的选取较为敏感。CAM3方案模拟强热带气旋的能力较其他方案偏好,ACM方案在多数年份模拟的热带气旋个数偏多,且在不同月份模拟的热带气旋生成频率与观测最接近,CAM3方案模拟的热带气旋出现频次与观测的偏差在大部分地区偏小。综合来看,CWRF模式中边界层参数化选用CAM3方案模拟热带气旋活动的性能较好。