西北太平洋热带气旋潜在生成指数的改进

热带气旋潜在生成指数(GPI,Genesis Potential Index)是热带气旋生成可能性大小的空间分布函数,利用大尺度环境场可以应用于热带气旋活动的季节预报,并且可以评估全球气候变化对热带气旋活动的影响。但是目前的GPI基本都是针对全球热带气旋活动构建的,没有考虑到热带气旋不同活动地区及其内部的差异。本研究考虑到南海和西北太平洋热带气旋生成的不同特点,分别构建了适用于南海(5～25°N,100～120°E)和西北太平洋(5～40°N,120～180°E)的热带气旋GPI。改进后的GPI对南海和西北太平洋区域热带气旋生成具有较好的模拟能力,不仅能很好地模拟南海和西北太平洋热带气旋生成频数空间分布的气候特征(相似系数为0.67),而且能够较好地模拟热带气旋生成在年际时间尺度上的空间分布特征。     

区域耦合模式FROALS模拟的西北太平洋热带气旋潜势分布与年际变率:耦合与非耦合试验比较

热带气旋潜势指数可以合理刻画热带气旋生成的位置与范围, 被广泛应用于评估气候系统模式对热带气旋的模拟。本文使用区域海—气耦合模式FROALS对西北太平洋地区1982～2007年的积分结果, 检验了该模式对热带气旋潜势指数的气候态和年际变率模拟能力, 并从决定热带气旋潜势的五个变量角度, 分析了造成模式模拟偏差的原因。结果表明, 模式可以合理再现西北太平洋地区热带气旋潜势指数的分布, 但由于西北太平洋季风槽模拟偏弱且耦合后模拟海温偏冷, 使得耦合试验模拟的热带气旋潜势指数分布偏弱, 尽管较之单独大气模式, 其模拟的空间分布有改善。在年际变率方面, 模式可以合理再现年际变率中热带气旋潜势指数对ENSO的响应, 且耦合模式优于单独大气模式, 分析表明其原因在于耦合模式模拟的850 hPa季风槽强度与年际变率优于单独大气模式。因此区域耦合模式在模拟热带气旋指数年际变率方面相较大气模式有优势。     

Impact of resolution and downscaling technique in simulating recent Atlantic tropical cylone activity

Using the global environmental multiscale (GEM) model, we investigate the impact of increasing model resolution from 2° to 0.3° on Atlantic tropical cyclone activity. There is a clear improvement in the realism of Atlantic storms with increased resolution, in part, linked to a better representation of African easterly waves. The geographical distribution of a Genesis Potential Index, composed of large-scales fields known to impact cyclone formation, coincides closely in the model with areas of high cyclogenesis. The geographical distribution of this index also improves with resolution. We then compare two techniques for achieving local high resolution over the tropical Atlantic: a limited-area model driven at the boundaries by the global 2° GEM simulation and a global variable resolution model (GVAR). The limited-area domain and high-resolution part of the GVAR model coincide geographically, allowing a direct comparison between these two downscaling options. These integrations are further compared with a set of limited-area simulations employing the same domain and resolution, but driven at the boundaries by reanalysis. The limited-area model driven by reanalysis produces the most realistic Atlantic tropical cyclone variability. The GVAR simulation is clearly more accurate than the limited-area version driven by GEM-Global. Degradation in the simulated interannual variability is partly linked to the models failure to accurately reproduce the impact of atmospheric teleconnections from the equatorial Pacific and Sahel on Atlantic cyclogenesis. Through the use of a smaller limited-area grid, driven by GEM-Global 2°, we show that an accurate representation of African Easterly Waves is crucial for simulating Atlantic tropical cyclone variability.     

提高模式分辨率后热带气旋生成迟缓的原因分析

利用目前国际上最先进的中尺度WRF模式模拟热带气旋生成,网格分辨率从9 km增加到3 km,3 km网格中积云参数化方案不起作用,依靠微物理方案来模拟对流尺度系统特征,模式中热带气旋的生成过程变得迟缓。当低压扰动发展到一定程度后再加入3 km网格,生成过程有加快趋势。本研究针对该现象进行分析。结果表明:只用微物理方案使低层(950～700 hPa)风速的垂直切变减小,不利于对流发展;切变减小主要是由于动量垂直输送项的差异所致。在加入细网格的6 h内,低层对流尺度(减去区域平均)的动量垂直输送量平均增加了一倍,某些时刻达到了5倍以上;动量混合增加是由于微物理方案模拟的垂直速度增加所致。此外,只用微物理方案导致对流有效位能迅速被消耗。低层垂直切变和对流有效位能的减小都不利于对流发展,从而导致热带气旋生成发展过程迟缓。本研究表明,目前WRF中的微物理方案在模拟热带气旋生成过程中的对流发展时仍然存在问题。     

西北太平洋热带气旋生成客观预测模型

该文提出一种西北太平洋热带气旋年生成活动的客观预测模型。研究大尺度环境因子对西北太平洋热带气旋年生成频次的作用,使用最小角回归算法对初始14个预测因子进行选择和降维,将资料集分为训练集(1979—2015年)和验证集(2016—2020年),建立随机森林回归模型预测热带气旋年生成频次。分析环境因子对西北太平洋热带气旋生成位置的作用,使用逐步回归算法筛选影响显著的预测因子,建立局部泊松回归模型预测热带气旋生成空间位置的概率。结果表明:随机森林回归模型可以预测西北热带气旋频次的主要变化和趋势,揭示环境因子对西北太平洋热带气旋年生成频次的影响。局部泊松回归模型对于气旋生成位置概率有一定预测能力。利用随机森林回归模型和局部泊松回归模型模拟1979—2020年西北太平洋热带气旋生成,结果与观测基本一致,可见模型可为热带气旋危险性分析提供参考。     

Changes in the Tropical Cyclone Genesis Potential Index over the Western North Pacific in the SRES A2 Scenario

The Tropical Cyclone Genesis Potential Index (GPI) was employed to investigate possible impacts of global warming on tropical cyclone genesis over the western North Pacific (WNP). The outputs of 20th century climate simulation by eighteen GCMs were used to evaluate the models’ ability to reproduce tropical cyclone genesis via the GPI. The GCMs were found in general to reasonably reproduce the observed spatial distribution of genesis. Some of the models also showed ability in capturing observed temporal vari...     

Understanding of the Effect of Climate Change on Tropical Cyclone Intensity: A Review

The effect of climate change on tropical cyclone intensity has been an important scientific issue for a few decades.Although theory and modeling suggest the intensification of tropical cyclones in a warming climate,there are uncertainties in the assessed and projected responses of tropical cyclone intensity to climate change.While a few comprehensive reviews have already provided an assessment of the effect of climate change on tropical cyclone activity including tropical cyclone intensity,this review focuses mainly on the understanding of the effect of climate change on basin-wide tropical cyclone intensity,including indices for basin-wide tropical cyclone intensity,historical datasets used for intensity trend detection,environmental control of tropical cyclone intensity,detection and simulation of tropical cyclone intensity change,and some issues on the assessment of the effect of climate change on tropical cyclone intensity.In addition to the uncertainty in the historical datasets,intertwined natural variabilities,the considerable model bias in the projected large-scale environment,and poorly simulated inner-core structures of tropical cyclones,it is suggested that factors controlling the basin-wide intensity can be different from individual tropical cyclones since the assessment of the effect of climate change treats tropical cyclones in a basin as a whole.     

南海与西北太平洋地区夏季热带气旋潜在生成指数的改进

现阶段使用的热带气旋潜在生成指数(Genesis Potential Index,GPI)在气候场的空间分布上能很好地拟合热带气旋的生成情况,但在热带气旋的年际变化拟合上效果很差。本研究考虑了相对涡度在热带气旋年际变化拟合上的重要作用,并以此为出发点,尝试改善GPI在西北太平洋地区的拟合效果。基于对1979—2011年美国联合飓风警报中心提供的热带气旋最佳路径数据和NCEP/NCAR再分析资料数据集的研究,将之前GPI中的绝对涡度项替换为修正过的相对涡度项。科氏力项仍然保留;将南海(100°～120°E,5°～25°N)与西北太平洋地区(120°～180°E,5°～40°N)热带气旋生成的差异性也纳入了考量,并在这两个区域分别构建GPI公式,改善了对热带气旋生成的气候分布模拟。除此之外,较之已存的GPI指数,改进后的GPI还很大程度提高了GPI对热带气旋生成年际变化的拟合效果,特别是对弱热带气旋年际变化的拟合效果有了显著提升。     

多种再分析资料中热带气旋潜在生成指数分析

根据7套再分析资料计算的热带气旋潜在生成指数(GPI),分析了GPI对西北太平洋区域台风盛季(7—9月)热带气旋生成的表征能力。结果表明,虽然这些再分析资料计算得到的GPI的空间分布与观测的热带气旋生成特征都比较一致。但是,在时间变化上7套再分析资料计算的GPI对观测热带气旋生成的表征能力差异较大,其中ERA-40(欧州中期天气预报中心再分析资料)和MERRA(美国国家航空和航天局研究和应用再分析资料)的GPI与观测的相关系数较高。进一步分析表明,各套资料GPI之间时间变化的差异主要来自相对湿度,而ERA-40和MERRA的GPI与观测值有较高的相关系数,也与相对湿度有密切关系。     

西北太平洋台风季节预报的数值模拟

利用中尺度气象模式WRF（weather research and forecasting）对2006年7月1日-9月30日的西北太平洋夏季台风进行了动力季节预报试验。结果表明：1）在对3个月以内的台风作动力季节预报试验时,WRF模式模拟的台风总个数与实况接近,模式模拟的总登陆台风数与实况相比偏小。从各月模拟情况看,台风总数与登陆数的模拟均与实况有差距。WRF模式对台风强度的模拟总体偏弱。2）WRF在模拟2006年7q月台风以及平均高度场、水平风垂直切变时,7月与实况接近,随时间增长,与实况的差别明显增大．WRF模式具有一定的台风动力季节预报能力,但其预报时限有待探讨。     

STOCHASTIC SIMULATION OF TROPICAL CYCLONE TRACKS IN THE NORTHWEST PACIFIC REGION WITH CLASSIFICATION MODEL

Accurate simulation of tropical cyclone tracks is a prerequisite for tropical cyclone risk assessment. Against the spatial characteristics of tropical cyclone tracks in the Northwest Pacific region, stochastic simulation method based on classification model is used to simulate tropical cyclone tracks in this region. Such simulation includes the classification method, the genesis model, the traveling model, and the lysis model. Tropical cyclone tracks in the Northwest Pacific region are classified into five categories on the basis of its movement characteristics and steering positions. In the genesis model, Gaussian kernel probability density functions with the biased cross validation method are used to simulate the annual occurrence number and genesis positions. The traveling model is established on the basis of the mean and mean square error of the historical 6 h latitude and longitude displacements. The termination probability is used as the discrimination standard in the lysis model. Then, this stochastic simulation method of tropical cyclone tracks is applied and qualitatively evaluated with different diagnostics. Results show that the tropical cyclone tracks in Northwest Pacific can be satisfactorily simulated with this classification model.     

Tropical Cyclone Genesis Potential Index over the Western North Pacific Simulated by LASG/IAP AGCM

Tropical cyclone genesis potential index(GPI) is a useful metric for gauging the performance of global climate models in the simulation of tropical cyclone(TC) genesis.The performance of LASG/IAP AGCM GAMIL2.0 in the simulation of GPI over the western North Pacific(WNP) is assessed in this paper.Since GPI depends on large scale environmental factors including low-level vorticity at 850 hPa,relative humidity at 700 hPa,vertical wind shear between 850 and 200 hPa,maximum potential intensity(MPI),and vertical velocity,the bias of GPI simulation is discussed from the perspective of thermal and dynamical factors.The results are compared with the ECMWF reanalysis data(ERA40).The analyses show that both the climatological spatial pattern and seasonal cycle of GPI over the WNP are reasonably simulated by GAMIL2.0,but due to the overestimation of relative humidity,the simulated GPI extends to 170°E,about 10°east to that in the reanalysis data.It is demonstrated that the bias in the simulation of monsoon trough,which is about 5°north to the reanalysis,leads to an overestimation of GPI during May-June and September-October,but an underestimation during July-August.Over the WNP,the response of GPI to ENSO is well captured by GAMIL2.0,including the eastward(westward) shift of TC genesis location during El Nin o(La Nin a) years.However,the anomalous convective center associated with El Nin o shifts westward about 20°in comparison to ERA40,which leads to the biases in both vertical velocity and relative humidity.These eventually result in the westward deflection of the boundary between the positive and negative GPI centers along 20°-30°N.The results from this study provide useful clues for the future improvement of GAMIL2.0.     

NUIST地球系统模式模拟热带气旋活动的气候特征分析

采用恒定的现代外部强迫驱动第一版NUIST地球系统模式,进行了40年全球热带气旋活动模拟,分析了热带气旋活动的气候特征,并与1977—2016年观测资料对比分析。结果表明：该模式能够模拟出与热带气旋类似的结构特征,在热带气旋活动活跃的海区,模拟热带气旋生成的空间分布和影响范围与观测基本一致,但是各个海区热带气旋的生成频数与观测还存在差异。除了北印度洋海区,各个海区热带气旋生成频数的季节变化与观测相似。模式在西北太平洋海区模拟结果最好,能模拟出热带气旋的生成范围和盛行路径;在北印度洋地区模拟结果较差,北印度洋海区的相对涡度模拟与观测存在较大差异,这是模式未能模拟出北印度洋热带气旋双峰特征的主要原因。     

ENVIRONMENTAL INFLUENCES ON NORTHWEST PACIFIC TROPICAL CYCLONE NUMBERS

In this study,the relationship between tropical cyclone numbers in the Northwest Pacific,Southern Oscillation (SO) and some environmental variables observed over the global oceans has been examined.The major results indicate that the pattern of correlations between the tropical cyclone numbers and the environmental variables is in a sense analogous to that between the SO and the same environmental variables,but the correlation is weak.The study indicates that the relationship between tropical cyclone numbers and environmental variables is more complex,and the factors affecting the variation in tropical cyclone numbers in the Northwest Pacific should include not only ENSO events but also a long-term effect which is not related to ENSO.     

初始涡旋结构对热带气旋强度变化影响的数值研究

本文利用中尺度WRF模式,通过构造3个位于不同高度上强度相同的初始涡旋暖心中心(分别称为Low试验、Mid试验和High试验),认识暖心垂直结构对热带气旋发展的影响。理想数值试验发现,在积分6 h后在Low试验和Mid试验中最大风速半径开始收缩,眼墙内对流发展,高层暖心发展明显比High试验强,强度增加明显快于High试验,达到快速增强的标准。进一步诊断发现,暖心偏低的试验中初始CAPE值较大,低层风垂直切变较强,有利于眼墙内对流发展,非绝热加热在高层暖心形成过程中起重要作用,最大风速半径收缩比High试验快,热带气旋强度快速增加。本研究清楚表明,数值预报模式中构造初始涡旋的暖心高度对模拟热带气旋的强度发展有重要影响。     

BCC_CSM模式对热带降水年循环模态的模拟

本文评估了国家气候中心发展的两个不同分辨率海—陆—气—冰多圈层耦合气候系统模式BCC_CSM1.1和BCC_CSM1.1 (m) 对热带降水两个年循环模态——揭示降水冬夏季节差异的季风模态和揭示过渡季节春季和秋季非对称特征的春秋非对称模态的模拟能力,讨论了模拟偏差产生的可能原因。分析结果表明,BCC_CSM1.1和BCC_CSM1.1 (m) 均能合理再现全球年平均降水的基本分布特征,也能较合理再现热带降水年循环模态的基本分布特征,尤其季风模态中降水与环流关于赤道反对称的特征;能够较合理再现春秋非对称模态与热带海洋表面温度(SST)年循环之间的关系。大气温度场、环流场以及热带SST的模拟偏差对降水季风模态有影响;热带SST年循环的偏差对降水春秋非对称模态的模拟偏差有贡献;模式分辨率对降水年循环模态的模拟也有一定影响。对比分析显示,大气模式和陆面模式水平分辨率提高之后模式在某些模拟性能上有所提高,这表现在:BCC_CSM1.1 (m) 模拟的1～12月降水气候态的空间变率更接近观测;热带海表温度年循环总体上更接近观测;模拟的热带降水年循环模态的部分特征更合理。但BCC_CSM1.1 (m) 的模拟结果相对观测仍存在较大偏差,有待进一步改进。     

SVM方法在热带气旋降水预报中的应用

应用国家气象中心下发的热带气旋报文资料（中心经纬度、中心气压、近中心最大风力）,设计了诸如热带气旋中心与嘉兴市的最近距离等因子,并任选3个因子组成三维坐标（x,y,z）,计算嘉兴市热带气旋降水的概率分布函数。利用SVM回归方法对选中的概率分布函数进行训练,建立嘉兴市热带气旋降水预报方法,并应用于业务试报。同时和多元回归方法进行历史回报和业务试验比较。结果表明,概率分布函数与热带气旋降水具有较好的相关性,SVM回归方法在嘉兴市热带气旋降水预报中的回归预报模型和业务化效果明显优于多元回归。     

基于气候系统模式FGOALS-g2的热带气旋活动及其影响的动力降尺度模拟

热带气旋是气候模拟关注的重要对象,但是,由于当前的气候系统模式分辨率较低,难以合理再现热带气旋分布特征,因此,动力降尺度就成为一种有效的手段。本文使用区域气候模式RegCM3,对中国科学院大气物理研究所气候系统模式FGOALS-g2的模拟结果进行动力降尺度,基于热带气旋路径追踪法,从热带气旋的路径、强度和降水三个方面,检验了动力降尺度在热带气旋模拟能力上的增值。结果表明,动力降尺度结果大幅提升了热带气旋路径频率的模拟,较之全球模式,其与观测的路径频率分布的空间相关系数从0.57提升至0.74;区域模式模拟的热带气旋强度与观测更为一致,全球模式难以模拟40 m s?1以上风速的热带气旋,区域模式能够模拟风速为60 m s?1的热带气旋;在热带气旋降水方面,降尺度后的热带气旋降水贡献率和平均热带气旋降水强度均有所改善,在西北太平洋区域较之全球模式,区域模式将热带气旋降水贡献率和降水强度提高了10%和4.7 mm d?1。动力降尺度后TC（tropical cyclone）的模拟技巧得到提升的区域为西北太平洋区域,但在中国南海区域,技巧提升的不显著甚至有所下降。关于动力降尺度结果在西北太平洋区域的技巧提升,分析表明能够更好体现CISK（Conditional Instability of the Second Kind）机制是主要原因,区域模式模拟的水汽增多、正涡度增强、上升运动增强而垂直风切变减弱都有显著贡献。     

Fine-resolution regional climate model simulations of the impact of climate change on tropical cyclones near Australia

Fine-resolution regional climate simulations of tropical cyclones (TCs) are performed over the eastern Australian region. The horizontal resolution (30 km) is fine enough that a good climatological simulation of observed tropical cyclone formation is obtained using the observed tropical cyclone lower wind speed threshold (17 m s^–1). This simulation is performed without the insertion of artificial vortices (bogussing). The simulated occurrence of cyclones, measured in numbers of days of cyclone activity, is slightly greater than observed. While the model-simulated distribution of central pressures resembles that observed, simulated wind speeds are generally rather lower, due to weaker than observed pressure gradients close to the centres of the simulated storms. Simulations of the effect of climate change are performed. Under enhanced greenhouse conditions, simulated numbers of TCs do not change very much compared with those simulated for the current climate, nor do regions of occurrence. There is a 56% increase in the number of simulated storms with maximum winds greater than 30 m s^–1 (alternatively, a 26% increase in the number of storms with central pressures less than 970 hPa). In addition, there is an increase in the number of intense storms simulated south of 30°S. This increase in simulated maximum storm intensity is consistent with previous studies of the impact of climate change on tropical cyclone wind speeds.     

西北太平洋热带气旋潜势分布和年际变率的数值模拟

热带气旋潜势指数是定量表征影响热带气旋生成的大尺度环境条件指标,在不能显式模拟热带气旋的气候系统模式中,常被作为热带气旋的代用指标。基于中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的AGCM GAMIL2.0模式在历史海温驱动下的积分结果,评估了该模式对热带气旋潜势气候态、季节循环和年际变率的模拟能力。并分别从影响热带气旋潜势分布的热力因子(相对湿度、热带气旋最大风速)和动力因子(垂直风切变、绝对涡度、垂直抬升速度)的角度,讨论了造成热带气旋潜势模拟误差的原因。结果表明,在西北太平洋地区,模式能够合理再现热带气旋潜势的气候态分布,但由于GAMIL2.0模拟的相对湿度偏大且向东延伸,造成了热带气旋潜势大值区较之再分析资料偏大且偏东10°。由于GAMIL2.0模拟的季风槽位置偏北偏强,导致模拟的热带气旋潜势季节循环北进偏早而南退偏晚。在年际变化方面,GAMIL2.0能合理模拟出热带气旋潜势在ENSO正负位相东西反向的变化特征,但位于20°—30°N的加强和减弱区的分界线偏西,这与模拟的垂直速度和相对湿度的模拟误差有关,进一步分析表明,这是由于模拟中ENSO事件期间的西北太平洋异常上升中心比观测偏西且偏强造成的。