海洋温带气旋发生发展的研究

本文综合地评述了近年来海洋温带气旋发生、发展的研究成果,讨论了海洋温带气旋爆发性发展的气候特征、天气形势、各种物理机制及数值模拟的结果,并进一步指出了有待解决的问题。     

北美温带气旋及其对纽约降水的影响

利用西半球１９８０－１９９０年常规天气图资料及纽约逐日降水资料，将冬半年北美温带气旋分为３类，分析了它们的气候特征，形成过程及其对纽约降水的影响。结果表明：北美温带气旋冬半年平均频数５１个，年际变化不大，月际分布最多月为１２个，最少月只有５个；不同类型气旋的时间分布及对纽约降水的影响存在明显差异。     

温带气旋概念模式的最新进展

一、引言回顾温带气旋概念模式发展的历史,常引证挪威锋面气旋模式(Bjerknes 和 Sol-berg,1922)作为随后概念发展的起点。然而,Kutzbach(1979)的独特历史见解提醒我们,那些重要的结构上及动力上的概念化过程,是在前一世纪由欧洲及美国气象学家发展的。我们先介绍这些先驱探索者提出的模式个例,认识一下他们敏锐的洞察力和对我们气象学遗产宝库所作的贡献。接着,有选择地讨论了从挪威“Bergen”气象学派时代到现在为止几个气旋锋面模式的发展,其中包括从外场研究和数值模拟中得到的最新进展。     

近50 a春季东亚温带气旋活动频数的气候特征及其变化

根据1948-2000年共53 a的NCEP/NCAR逐日海平面气压再分析资料,分析了春季(3、4、5月)东亚内陆和沿海地区气旋活动频数、气旋移动路径等气候特征及其年际、年代际变化,结果表明在春季的3、4、5月份中,内陆存在三个明显的气旋活动频数较大的地区,分别位于101°E、45°N附近的蒙古高压南缘、贝加尔湖以东的115°E、53°N附近地区和126°E、53°N我国东北北部附近地区.蒙古地区春季气旋活动频数存在明显的年代际变化,50年代气旋活动频数较少,60年代开始到70年代后期气旋活动频数较多,从70年代末至今又进入一个气旋活动频数较少的时期.贝加尔湖东部地区在50年代初气旋活动频数较多,50年代中期到60年代中期气旋活动频数较少,而60年代后期到70年代后期气旋活动频数又较多,此后气旋活动频数逐渐减少.我国东北地区春季各月气旋活动频数没有明显的年代际变化,只有80年代以来气旋活动频数的振幅较大.东亚沿海春季气旋活动频数较高的地区主要位于我国东北到俄罗斯远东和我国长江中下游到日本一带.从气旋活动路径来看,我国长江中下游到日本一带气旋活动路径在各个年代基本相同,没有明显的年代际变化,而我国东北到俄罗斯远东地区气旋活动路径在不同年代略有差异.进一步分析发现,气旋活动频数与北方地区春季降水量及沙尘暴发生次数具有一定关系.     

卫星云图在温带气旋发生发展中的应用

本文对１９７３年１月－１９８８年１２月的卫星云图资料进行研究，分析了此阶段中发生的温带气旋云图特征，并归纳了温带气旋发生发展的云图特征，文中给出了一些中，短期预报方法和判据。在实际预报工作中收到了较好的效果。     

爆发性与非爆发性海洋温带气旋

本文选取分别代表爆发性发展(1983年3月)和非爆发性发展(1982年3月)的两个海洋温带气旋个例,对它们进行了比较研究。结果表明,无论是在基本要素场,还是诊断出的物理量场,两者都表现出明显的差异。其中,涡度、位势涡度、扰动动能和总动能之间的差别更大。在爆发阶段,前3项的增加量爆发性气旋是非爆发性气旋的2—4倍,而总动能的增大值两者悬殊更大,比值为13.6:1。     

北半球温带气旋的变化

许多学者对近半个世纪以来温带气旋的频数、强度和路径的年际、年代际变化等特征进行了研究,并探讨了温带气旋变化与大气环流的关系,试图揭示气候变暖背景下温带气旋变化的可能原因。较为一致的研究结论是：在全球变暖背景下,北半球气旋活动的变化显示出在中纬度明显减少,而在高纬度增加的趋势,意味着气旋的路径已经明显地北移。研究还表明,气旋活动的变化与对流层斜压性、急流以及北大西洋涛动、海温梯度等因素有关。     

辽宁省温带气旋龙卷的环境参数特征

利用欧洲中期天气预报中心ERA5再分析数据,统计1979—2020年辽宁省42个温带气旋龙卷环境背景和物理量参数特征,结果表明:辽宁省温带气旋龙卷多发于温带气旋中心的西南、东南象限,与冷锋前暖区相对应,主要分布在辽河平原中西部及渤海湾沿岸,强龙卷(EF2及以上级别)占比为28.6%。风暴相对螺旋度和对流有效位能的大值区出现在气旋西南—东南象限,呈带状分布,龙卷风暴主要分布于风暴相对螺旋度大值区西北侧、对流有效位能大值区的顶端的强梯度区附近。强龙卷参数最大值达0.7,其大值区与EF2及以上级别龙卷相对应。地面冷锋和干线是温带气旋龙卷的关键触发系统,对比近气旋中心和冷锋尾部湿度垂直分布,后者所表现的高层强干侵入导致风暴产生更强的冷池,过强的下沉气流可能是龙卷产生的不利因素。温带气旋龙卷多分布于高空急流左侧气流的分流区内,对应高空强辐散区。0~3 km垂直温度递减率大值区与气旋中心附近的弱龙卷高发区有较好对应关系。     

A Modified Algorithm for Identifying and Tracking Extratropical Cyclones

In this study, a modified identification and tracking algorithm for extratropical cyclones is developed. This identification scheme is based on triangular-mesh contouring techniques combined with a connected-component labeling method in order to detect the outer boundaries and spatial domain characteristics of individual cyclones. A new tracking method allowing for the identification of cyclone merging and splitting events, as well as short-lived windstorms, is developed to reduce the uncertainty in the tracking of extratropical cyclones. I also show that this method excludes the tracks of open systems that would have been unnecessarily detected using conventional NCP methods. The climatological features of the distribution of cyclone frequencies are substantially larger over the traditional storm track regions compared to those seen in previous studies. Interestingly, a significant increase in the cyclone density in the Arctic occurs during all four seasons(up to 19%in summer) compared to that seen with a latitude–longitude gridded mesh analysis. I develop two new regional intensity indices(depth and vorticity) based on the cyclonic domain to better quantify the cyclonic activity in the Arctic region, and find that the interannual variabilities in these two indices are highly consistent. The results of this analysis may shed light on high-latitude cyclonic behavior studies via the newly detected 2D cyclone atlas derived from this cyclonic-domain-based algorithm.     

Cyclone Phase Space Characteristics of the Extratropical Transitioning Tropical Cyclones over the Western North Pacific

The cyclone phase space (CPS) method has been utilized to evaluate the extratropical transition (ET) of tropical cyclones (TCs) in many recent publications. However, these studies mainly focused over the North Atlantic basin. In this paper, the CPS characteristics of all the cyclones over the western North Pacific are investigated and discussed, with three parameters calculated from the best-track data of the Regional Specialized Meteorological Center in Tokyo and the Japanese 25-yr reanalysis data. It is concluded that most TCs over the western North Pacific possess the non-frontal and warm-core structure, while a larger number of cyclones that have undergone ET hold the frontal and cold-core structure. The spatial pattern of the CPS parameters indicates that the areas of tropical and extratropical cyclone activities could be demarcated by 30°N. The composite and individual series of three parameters of the CPS indicate that the transformation of −V _T^U from positive to negative leads to the start of ET, and could be considered as a potential predictor in operationally forecasting an ET event.     

A Comparison of Precipitation Distribution of Two Landfalling Tropical Cyclones during the Extratropical Transition

The precipitation distributions associated with two landfalling tropical cyclones(TCs) during extratropical transition(ET) were examined in this study.Their distinction is that the bulk of precipitation fell to the left of the TC track in one TC and to the right in the other.The analyses indicate that,for the TC Haima(2004) case,accompanied by the approach of a deep midlatitude trough throughout the depth of the troposphere,the warm and moist air advection by the southeasterly flow north of TC was favorable for warm advection and frontogenesis to the northwest of the TC.Due to the steepening of equivalent potential temperature(θ e),the air-parcel uplift along the θ e surface,in collaboration with thermally direct circulation related to frontogenesis,led to enhanced precipitation northwest of the TC.In contrast,for TC Matsa(2005) embedded within a moister environment,a weak midlatitude trough was situated at the mid-upper level.The convection was triggered by the conditional instability at the lower level and then sustained by dynamic forcing at the mid-upper level so that the heavy precipitation occurred to the northeast of TC.For the two TC cases,the precipitation enhancement was also linked to the upper-level anomalous divergence associated with the jet-related forcing on the right side of the jet entrance.From the quasigeostrophic perspective,the advection of geostrophic absolute vorticity by the thermal wind most likely served as an indication reflecting the displacement of the vertical motion relative to the center of the TC.     

Impact of the Subtropical High on the Extratropical Transition of Tropical Cyclones over the Western North Pacific

Recent publications have investigated the interactions between the extratropical transitions （ETs） of tropical cyclones （TCs） and midlatitude circulations; however, studies of ET events have rarely considered the relationship between the storm and the nearby subtropical high. The TC best-track data provided by the Regional Specialized Meteorological Center-Tokyo Typhoon Center of the Japan Meteorology Agency are used in conjunction with the NCEP/NCAR reanalysis data to discuss the potential effects of the subtropical high on ETs over the western North Pacific basin. When the western Pacific subtropical high （WPSH） is weakened and withdrawn toward the east, more TCs follow recurving paths and the midlatitude trough activity is intensified. These changes lead to enhanced ET activity. By contrast, when the WPSH strengthens and extends westward, the number of TCs that follow direct westward paths increases and the midlatitude trough is relatively inactive. These conditions lead to reduced occurrences of ET cases. Abnormal activity of the WPSH should be considered as an important factor in determining ET activity.     

西风带高空槽对登陆我国变性热带气旋的影响及其机理研究

应用日本气象厅1979~2008年的热带气旋资料以及日本25年 (JRA-25) 再分析资料, 本文首先对登陆我国变性加强和变性减弱的两类热带气旋进行了合成对比分析, 发现热带气旋变性后的强度变化与相应的西风带高空槽的强弱有很好的对应关系。然后, 我们选取了2004年登陆我国的热带气旋Haima为研究对象, 通过中尺度模式模拟再现了其登陆后变性演变过程, 采用片段位涡反演方法改变了模式初始高空槽的强度, 研究了高空槽强度的变化对Haima变性过程的影响。研究表明: (1) 高空槽加强 (减弱) 后, Haima移速明显加快 (减慢), 此外深 (浅) 槽对应的Haima变性加强过程中心气压降幅较大 (小); (2) 不同强度的高空槽与Haima相互作用的过程中, 深槽对应的高空急流范围较大, 强度更强, 相应的高空强辐散有利于Haima明显的再发展; (3) 另外深槽对应着较强的高层正位涡带, 正位涡向下伸展诱发低层Haima正位涡明显增长, 从而导致低层锋区的强烈发展和低层气旋的明显加强。     

Re-Examination of the Potential Vorticity Metrics for Determining Extratropical Transition Onset and Completion Times Using High-Resolution Data

Based on a high-resolution dataset, this note re-examines the recently developed potential vorticity （PV） metrics for determining extratropical transition （ET） onset and completion times. The PV metrics use average 330-K isentropic potential vorticity （IPV） to determine the ET onset time, defined as the 330-K IPV minimum time. However, the suggested 330-K IPV threshold fails to determine the ET completion time using the 20-km resolution data, and this IPV method cannot resolve reintensifying and weakening tropical cyclone cases due to the absence of differentiation of lower-level IPV tendencies after ET onset between these two groups of cases.     

两类登陆热带气旋的大尺度环流特征分析

采用动态合成分析方法,对1970-2006年登陆后北上类TC（tropicalcyclone）和西行类TC各7个样本做动态合成分析和诊断,结果表明：（1）北上类TC在背景场长波槽前北移靠近中纬度斜压锋区,通过吸附运动使TC低压并入西风槽,而西行类TC背景场没有长波槽,离中纬度斜压锋区较远;（2）北上类TC登陆时存在西南低空急流水汽输送带,当其强度减弱后,TC东南侧存在东南暖湿气流作为补充,而西行类TC减弱后逐渐与之分离,且不存在东南暖湿气流作为补充;（3）北上类TC高层辐散区与高空急流边界靠近,因此增强了其向东北方向的辐散,低层由于高层动量下传,加强了低空西风,从而使TC低压环流维持,而西行类TC离高空急流边界较远;（4）北上类TC从中纬度斜压锋区获取斜压能量,其环流垂直切变增强,相对涡度差负值增大,在高空TC中心散度由大变小后又由小变大的过程中,TC发生了变性,而西行类TC没有环境能量补给,逐渐填塞消亡。因此,当一个TC登陆后,其预报移动方向、水汽输送状况、与斜压锋区的关系以及高空辐散气流等特征,可以作为初步判定登陆TC将减弱消亡还是将变性加强的可能原因。