斜压大气中热带气旋运动特征的动力分析

从绝热、无摩擦、无环境场作用条件下的原始方程组出发,讨论了热带气旋的动力平衡特征,并分别导出了正、斜压大气中综合描述热带气旋中心强度变化的物理量(dI/dt)及其动力平衡关系式,进而分析了正、斜压大气中的热带气旋强度变化及移动的特征.结果表明:热带气旋的定常运动具有"相当地转风平衡”的特征,其等"压能”线和等位涡线均与流线重合;"β涡旋对”及由高(低)层水平风正(负)垂直切变产生的"切变涡旋对”之间的"通风气流”均使热带气旋的强度减弱,高(低)层涡度的负(正)垂直平流则增强热带气旋的强度;热带气旋的中心有向极、向高(低)层涡度垂直平流的梯(升)度方向移动的趋势,垂直运动及高、低层水平风速垂直切变的非对称结构对热带气旋的移动有影响;"γ效应”则是"通风气流”牵引热带气旋移动的动力机制之一.     

斜压大气中热带气旋运动特征的动力分析

从绝热、无摩擦、无环境场作用条件下的原始方程组出发,讨论了热带气旋的动力平衡特征,并分别导出了正、斜压大气中综合描述热带气旋中心强度变化的物理量(dI/dt)及其动力平衡关系式,进而分析了正、斜压大气中的热带气旋强度变化及移动的特征.结果表明:热带气旋的定常运动具有"相当地转风平衡”的特征,其等"压能”线和等位涡线均与流线重合;"β涡旋对”及由高(低)层水平风正(负)垂直切变产生的"切变涡旋对”之间的"通风气流”均使热带气旋的强度减弱,高(低)层涡度的负(正)垂直平流则增强热带气旋的强度;热带气旋的中心有向极、向高(低)层涡度垂直平流的梯(升)度方向移动的趋势,垂直运动及高、低层水平风速垂直切变的非对称结构对热带气旋的移动有影响;"γ效应”则是"通风气流”牵引热带气旋移动的动力机制之一.     

2014年两次路径相似热带气旋降水特征及其成因的对比

利用NASA的MERRA再分析数据、台站降水资料、热带气旋最佳路径数据集和雷达资料初步对比探讨了2014年两次路径相似台风（“威马逊”和“海鸥”）的降水特征及其成因.结果表明,两者台站过程降水和最大日降水强度差异明显;在华南产生的过程降水和日降水均表现出明显的非对称性,最强均在海南岛;在海南岛产生的过程降水、日降水和最大小时降水最强均在海南岛西部和北部.与“海鸥”相比,在强降水时段,“威马逊”产生更大台站日降水的原因之一是其自身更强的强度和偏慢的移动速度,而且还与高层更强的南亚高压主体、中层偏弱偏东的副热带高压和低层强的低空急流密切相关.在强降水阶段,两者所处的环境风垂直切变均指向西南偏西-西南偏南方向,而强的对流均主要在环境风垂直切变的左侧或前侧.两者强降水主要在海南岛西部和北部的关键原因是五指山山脉和台风路径的相对位置配置类似,强降水区恰好处于向岸风面或五指山的迎风面.

     

热带气旋榴莲(2001)生成的垂直耦合特征和机制

热带气旋(Tropical Cyclone,TC)生成过程中的垂直耦合过程及其机制,是一项隐含在TC生成关键因子——弱的水平风垂直切变条件下的,重要但尚未被解答的基础科学难题.文章通过实例数值模拟和理论分析对这一问题开展了针对性研究,主要结论如下:即使是发生在正压环境下的TC生成过程,仍然存在TC胚胎区的对流层中低层槽...     

海南井水位对热带气旋响应特征的分析

大量观测资料及实验研究证实,地下水对地壳应力-应变的响应频率较宽,可记录到地震波中的瑞利波(10～20 s)、潮汐波动(1/3～1/2 d)、气压波动(儿小时至几十天)等.在文献中,已见热带气旋引起地震仪的震颤波,倾斜仪和重力仪的“脉动加粗”等方面研究成果,但井水位对大气环流、雷暴高压、热带气旋等的响应,则未见报导.     

基于下投式探空仪资料的超强台风蔷薇(2008)动力和热力结构特征分析

本文主要利用全球定位下投式探空仪(dropsonde)资料和卫星云图资料,对2008年第15号超强台风蔷薇(Jangmi)边界层的热力和动力结构进行了分析,并且对其生命史中两个不同的时期的热力和动力结构特征进行了对比.结果表明:在内核区域中,距离眼越近,切向风越大,动力和热力边界层高度越低.边界层内,温度垂直递减率相比边界层以上更大;很多探空仪廓线中出现假相当位温(θse)垂直递减率与一般规律相反(即θse/z>0)的现象,并且能和径向风从流入转为流出以及Vr/z>0的高度很好的对应.对比生命史的不同时期,发现从台风发展的初始阶段到成熟阶段,在同一高度上切向风和径向风均有明显增大的趋势,径向流入层的厚度增大;台风内核区域的温度、比湿以及假相当位温都有增大的趋势,说明台风在发展增强的过程中从海表面获取了巨大的能量.     

东亚热带与副热带季风区对流降水和层云降水季节变化特征对比分析研究

利用10年TRMM卫星2A25资料,对东亚热带和副热带季风区对流降水和层云降水的季节变化特征进行了对比分析,研究了热带和副热带季风区降水性质的差异,并结合IPCC第4次报告中24个模式的20c3m模拟资料,对现有模式在东亚热带和副热带季风区关于对流降水及层云降水的模拟能力做了一个简单的评估,分析了模式中可能存在的问题.结果表明：夏季风爆发后,东亚热带与副热带季风区对流降水和层云降水都明显增加,但热带季风区对流降水所占比重明显减少,而副热带季风区对流降水所占比重明显增加,热带和副热带季风区存在明显不同;现有模式对东亚季风区对流降水百分比的模拟普遍偏高,而对层云降水的模拟偏少,这在热带季风区尤其明显;模式较好地模拟出了副热带季风区中对流降水百分比的季节变化特征,而对热带季风区对流降水百分比的季节变化没有正确描述;研究结果表明对流降水和层云降水在时间和空间上经常同时出现,具有很强的伴随性,而模式没有正确描述这种相关性,这可能是模式对层云降水百分比模拟不好的一个重要原因.     

An evaluation and improvement of tropical cyclone prediction in the western North Pacific basin from global ensemble forecasts

Forecasts of tropical cyclones(TCs) of the western North Pacific basin during the period of July to August 2018,especially of Rumbia(2018), Ampil(2018) and Jongdari(2018) that made landfall over Shanghai, have opposed great challenges for numerical models and forecasters. The predictive skill of these TCs are analyzed based on ensemble forecasts of ECMWF and NCEP. Results of the overall performance show that ensemble forecasts of ECMWF generally have higher predictive skill of track and intensity forecasts than those of NCEP. Specifically, ensemble forecasts of ECMWF have higher predictive skill of intensity forecasts for Rumbia(2018) and Ampil(2018) than those of NCEP, and both have low predictive skill of intensity forecasts for Jongdari(2018) at peak intensity. To improve the predictive skill of ensemble forecasts for TCs, a method that estimates adaptive weights for members of an ensemble forecast is proposed. The adaptive weights are estimated based on the fit of ensemble priors and posteriors to observations. The performances of ensemble forecasts of ECMWF and NCEP using the adaptive weights are generally improved for track and intensity forecasts. The advantages of the adaptive weights are more prominent for ensemble forecasts of ECMWF than for those of NCEP.     

热带气旋Rossby波能量频散问题研究进展

热带气旋是发生在热带洋面上的强烈气旋性涡旋.由于地转涡度梯度的存在,热带气旋在移动过程中不断发生Rossby波能量频散,并在热带气旋运动方向的后部激发出反气旋和气旋交替排列的Rossby波能量频散波列.多热带气旋共存和热带气旋的异常运动是当前国际热带气旋研究领域的热点问题,热带气旋Rossby能量频散被证实与多个热带气旋连续生成和异常运动密切相关.本文从热带气旋能量频散及波列特征、主要影响因子、反馈作用等方面,回顾总结了国内外关于热带气旋Rossby波能量频散的相关研究进展,并提出当前亟待解决的一些科学问题.目的是为深入研究热带气旋Rossby波能量频散及其影响提供基础和参考,以期使更多的研究学者关注热带气旋能量频散问题,从而进一步揭示热带气旋生成、发展和异常运动的动力学机理.

     

半个世纪来热带海洋风暴对中国大陆的影响

本文利用美国海军台风警报中心（JTWC）提供的1945～2002年热带风暴路径资料统计分析了西北太平洋（NWP）和中国南海（SCS）风暴生成及登陆中国大陆热带风暴的时空演变特征.季节变化上,NWP风暴登陆主要集中于6～11月,SCS风暴影响主要集中在6～9月,但后者登陆总数比前者少.西北太平洋风暴在东南沿海(27°N,120°E)附近登陆的频次最高,在此以北随纬度急剧下降.年际变化时间尺度上,登陆大陆的风暴年总数与来自南海的年风暴数成正比.登陆我国的热带风暴年频数有明显的区域差异和显著的2～7年振荡.长期趋势上,两个海域的风暴年生成频数和登陆大陆的年风暴频数在58年中总体呈线性增长趋势,其中登陆频数增长趋势相对缓慢,但近几年登陆风暴数与生成风暴数都表现出减少的趋势.生成频数和登陆频数都呈现出年代际变化,其年代转换发生在1960、1970年和1990年前后.     

西北太平洋热带气旋活动影响区域大尺度环流的数值模拟研究

本文利用"模式手术"方法研究了西北太平洋热带气旋（TC）对东亚-西北太平洋区域大尺度环流的影响.结果表明,夏季频繁的西北太平洋TC活动导致东亚夏季风增强,季风槽加深;西太平洋副热带高压东退,位置偏北;东亚副热带高空急流强度增强,北太平洋（东亚大陆）上急流轴偏北（偏南）;热带地区（副热带地区）的对流层中低层出现异常上升气流（下沉气流）,并且从低纬向高纬呈现异常上升气流和异常下沉气流交替分布特征.在中国东南沿海,TC降水导致夏季降水量明显增加;而在长江中下游和华北地区,TC活动引起的异常下沉气流使夏季降水量显著减少.因此,夏季西北太平洋TC活动对东亚-西北太平洋区域气候有显著影响.     

Interdecadal change of the linkage between the North Atlantic Oscillation and the tropical cyclone frequency over the western North Pacific

The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linkage appears to have an interdecadal change from weak connection to strong connection. During the period of 1948–1977, the NAO was insignificantly correlated to the WNPTCF. However, during the period of 1980–2009, they were significantly correlated with stronger(weaker) NAO corresponding to more(fewer) tropical cyclones in the western North Pacific. The possible reason for such a different relationship between the NAO and the WNPTCF during the former and latter periods is further analyzed from the perspective of large-scale atmospheric circulations. When the NAO was stronger than normal in the latter period, an anomalous cyclonic circulation prevailed in the lower troposphere of the western North Pacific and the monsoon trough was intensified, concurrent with the eastward-shifting western Pacific subtropical high as well as anomalous low-level convergence and high-level divergence over the western North Pacific. These conditions favor the genesis and development of tropical cyclones, and thus more tropical cyclones appeared over the western North Pacific. In contrast, in the former period, the impact of the NAO on the aforementioned atmospheric circulations became insignificant, thereby weakening its linkage to the WNPTCF. Further study shows that the change of the wave activity flux associated with the NAO during the former and latter periods may account for such an interdecadal shift of the NAO–WNPTCF relationship.     

春季Hadley环流异常对夏季西北太平洋热带气旋频数影响的数值模拟试验

观测事实揭示出春季Hadley环流与夏季西北太平洋热带气旋频数之间存在显著的负相关关系.由春季Hadley环流异常引起的西北太平洋地区夏季纬向风垂直切变、大气辐合辐散等的异常变化是这一关系存在的内在原因.本文通过数值试验对这一关系的真实性进行了验证,即利用中国科学院大气物理研究所发展的9层大气环流模式（IAP9L-AGCM）模拟了春季Hadley环流异常偏强情景,并分析了该情景下影响西北太平洋热带气旋生成的环境场的响应.结果表明,在春季Hadley环流偏强情景下,夏季西北太平洋地区纬向风垂直切变幅度加大,低空大气异常辐散,高空大气异常辐合,东亚夏季风减弱,这种环流背景不利于热带气旋生成和发展,因此,西北太平洋热带气旋频数异常偏少.数值模拟结果与已有的诊断结果相吻合,进而证实了春季Hadley环流与夏季西北太平洋热带气旋频数负相关关系的存在.因此,春季Hadley环流信号可以用于西北太平洋热带气旋活动的气候预测.     

Relationship between the Asian-Pacific oscillation and the tropical cyclone frequency in the western North Pacific

The relationship between the Asian-Pacific oscillation (APO) and the tropical cyclone frequency over the western North Pacific (WNP) in summer is preliminarily investigated through an analysis of ob- served data. The result has shown clearly that APO is significantly and positively correlated to the tropical cyclone frequency in the WNP. If APO is above (below) the normal in summer, more (less) tropical cyclones will tend to appear in the WNP. The present study also addresses the large-scale at- mospheric general circulation changes underlying the linkage between APO and the WNP tropical cy- clone frequency. It follows that a positive phase of summer APO is concurrent with weakened as well as northward and eastward located western Pacific subtropical high (WPSH), low-level convergence and high-level divergence, and reduced vertical zonal wind shear in the WNP, providing favorable envi- ronment for the tropical cyclone genesis, and thus more tropical cyclones will come into being, and vice versa.     

Relative role of subinertial and superinertial modes in the coastal long wave response forced by the landfall of a tropical cyclone

A set of numerical experiments has been performed in order to analyze the long-wave response of the coastal ocean to a translating mesoscale atmospheric cyclone approaching the coastline at a normal angle. An idealized two-slope shelf topography is chosen. The model is forced by a radially symmetric atmospheric pressure perturbation with a corresponding gradient wind field. The cyclone's translation speed, radius, and the continental shelf width are considered as parameters whose impact on the long wave period, modal structure, and amplitude is studied. Subinertial continental shelf waves (CSW) dominate the response under typical forcing conditions and on the narrower shelves. They propagate in the downstream (in the sense of Kelvin wave propagation) direction. Superinertial edge wave modes have higher free surface amplitudes and faster phase speeds than the CSW modes. While potentially more dangerous, edge waves are not as common as subinertial shelf waves because their generation requires a wide, gently sloping shelf and a storm system translating at a relatively high (∼10 m s⁻¹ or faster) speed. A relatively smaller size of an atmospheric cyclone also favors edge wave generation. Edge waves with the highest amplitude (up to 60% of the forced storm surge) propagate upstream. They are produced by a storm system with an Eulerian time scale equal to the period of a zero-mode edge wave with the wavelength of the storm spatial scale. Large amplitude edge waves were generated during Hurricane Wilma's landfall (2005) on the West Florida shelf with particularly severe flooding occurring upstream of the landfall site.     

Hadley环流的年际和年代际变化特征及其与热带海温的关系

利用NCEP/NCAR再分析风场资料和NOAA海表温度(SST)资料,分析了冬、夏季Hadley环流的变化特征及其与热带海温在年际、年代际尺度上的关系. 结果表明,冬季北半球Hadley环流强度具有明显的年际和年代际变化,同时还呈现出明显的增强趋势. 伴随着Hadley环流的加强,环流中心位置南移,高度上升;夏季南半球Hadley环流变化主要表现为强、弱、强的年代际振动,没有明显的线性趋势. 研究还显示冬季Hadley环流与Nino3区SST正相关,这种相关性具有年代际变化特征. 年际尺度上,冬季北半球Hadley环流与Nino3区SST正相关;夏季南半球Hadley环流与Nino3区SST负相关,即当赤道中东太平洋SST异常偏暖(冷)时,冬、夏季Hadley环流变强(弱).     

太阳天顶角对太湖恰在水面下辐照度比影响的定量分析

恰在水面下辐照度比变化与吸收系数、散射系数和太阳天顶角存在着密切的关系,而太阳天顶角对太湖恰在水面下辐照度比的定量影响程度尚不明确.为此,本文基于2010年5月太湖27个样点的水体光学参数和理论数值模拟,对太湖水体的情况进行研究.理论数值模拟结果表明:当太阳天顶角分别在0°～25°和70°～89°区间内变化时,对恰在水面下辐照度比增幅影响较小,增幅相差不到10%;而当太阳天顶角在30°～70°之间时,对辐照度比增幅影响很大,增幅为13.13%～52.19%.同时,利用实测数据对理论结果进行线性相关验证表明,此数值研究整体上符合太湖的实际情况.因此,对水体光学特性以及光对水生生态系统驱动作用研究的时候,应充分考虑太阳天顶角的影响.