2006年超强台风“桑美”强度突变的动能特征分析

应用NCEP/NCAR再分析资料,对2006年超强台风“桑美”（Saomai）强度突变过程的动能特征进行分析,结果表明：“桑美”突然增强时刻其低层总动能和旋转风动能突然增加,辐散风动能也有所增加,总动能的增加主要是由旋转风动能增加所引起的;其高层总动能和旋转风动能突然减小,而辐散风动能突然增加,高层动能下传是导致“桑美”突然增强的重要原因;“桑美”突然增强时刻高层辐散风动能向旋转风动能的转换达到最大,低层辐散风与旋转风相互作用动能项达到最大;“桑美”突然减弱时刻的高低层能量变化趋势与突然增强时刻相反,并存在着低层动能的上传;“桑美”强度突变时对总动能（K）、旋转风动能（KR）、辐散风动能（KD）变化的响应时间为6～18 h。     

干冷空气活动对热带气旋强度变化影响的研究进展与展望

热带气旋的强度变化一直是热带气旋研究中的重要内容之一,干冷空气活动与热带气旋强度变化之间有密切的关系,如快速增强和快速减弱过程。文章对国内外干冷空气影响热带气旋强度变化的研究成果进行了回顾和总结,主要包括干冷空气的强度、侵入位置,以及高空冷性天气系统对热带气旋强度变化的影响三个方面,并对未来的研究进行展望,以期为干冷空气影响热带气旋强度的研究提供参考。     

一次降雪过程持续原因分析

利用多种观测资料和中尺度数值模拟资料,对2011年2月14日发生在江淮地区的一次预报失误的持续性降雪过程进行较为全面的分析.结果表明:前期的降水导致近地面维持较大湿度,补充南下的冷平流促使低层大气接近饱和,降雪持续期间,水汽集中在对流层低层浅薄的层次中;对流层中层发展和维持的强冷平流导致降水区上空迅速降温减湿,从而在对流层中低层,逐渐建立起弱对流不稳定层结.而叠置其上的稳定层则将对流活动和水汽的向上输送限制在对流层低层内,使得水汽和能量得以在一定范围内集中;不断补充南下的冷空气强迫近地层风场发生扰动,形成的中尺度切变线,为这种浅薄层次下的弱对流活动提供了触发条件.尽管辐合抬升较弱,但与其它季节相比,气温较低的冬季,在抬升凝结高度较低的大气中,水汽易凝结成云致降水.造成这次预报失误的原因,是忽略了近地层系统的变化.另外,对补充冷空气的影响作用考虑不充分.     

2009年6月河南一次飑线过程的成因分析

利用地面观测资料、NCEP1°×1°再分析资料和雷达探测资料,从能量、动力和触发机制等角度,对2009年6月3日发生在河南东部地区的一次飑线过程进行综合分析。结果表明:东北冷涡是此次飑线过程的主要影响系统,涡后冷空气南下与低层暖湿空气叠加造成对流不稳定,高层的干冷空气侵入增强了对流不稳定;低层辐合、高层辐散为飑线强对流天气的发生发展提供了强烈上升运动的动力条件,地面维持并加强的干线所激发的次级环流可能是这次飑线系统发生发展的重要机制之一;中低层的垂直风切变稳定维持、加强、迅速减小与飑线强对流天气发生发展前后对应较好,其演变特征对此次飑线过程有很好的指示意义。     

对华北一次特大台风暴雨过程的位涡诊断分析

通过对９６０８号台风低压及其外围暴雨位和等熵面上物理量场的分析,揭示了台风低压北上诱发暴雨过程的位涡场的结构及冷空气对暴雨增幅的作用,给出此次暴雨增幅过程的图像。分析表明：对流层低层中高纬度冷空气（高位涡）扩散南下在台风低压环流区附近的“侵入”作用是此次特大暴雨过程的最重要的原因之一;等熵面位涡的分析进一步说明了中高纬地区冷空气的活动状况;对流层高层或平流层低层位涡的下传有利于位势不稳定能量的释放     

An Atmospheric Dry Intrusion Parameter and Its Application

Dry intrusion plays an important role in the explosive development of cyclones and the evolution of cold fronts. Characteristics of dry intrusion during a rainfall event that occurred in northern China are analyzed in detail in this paper. The IM (ingredients-based methodology) developed by Doswell et al. in 1996 and Wetzel and Martin in 2001 is utilized. All the physical representations of dry intrusion defined in the past studies, such as low relative humidity, cold advection, and high potential vorticity (on either isobaric or isentropic surfaces), are combined into a simple and convenient physical parameter to characterize dry intrusion. This is a new attempt to extend the IM that was primarily applied to research on heavy rainfall to the study of dry intrusion. The new dry intrusion parameter is used to analyze the isentropic evolution of dry intrusion during the rainfall event. The results show that this parameter can better quantify the intensity of dry intrusion and diagnose its evolution shown in satellite infrared and water vapor imageries.It is found that dry intrusion maintains during the rainfall period. The intensity of precipitation increases with the increasing dry intrusion, which has pushed the rainy region southeastward. From the results on the isentropic surface and the corresponding isobaric surface,it is inferred that the analyses of dry intrusion on both surfaces are consistent with each other. The isentropic analysis of dry intrusion reveals that cold and dry air at the upper level overruns that in the lower troposphere where moist and warm air is located.Thus, potential instability is built up in the vertical direction, which favors the occurrence of precipitation.In practice,we may identify dry intrusion regions by tracking strong signals of the dry intrusion parameter,and further identify the instability near the dry intrusion regions.This will aid in improving the accuracy of precipitation forecast.     

超强台风 “桑美” (2006) 近海急剧增强过程数值模拟试验

应用PSU/NCAR非静力平衡中尺度模式MM5 (V3.5) 设计试验方案, 对超强台风 “桑美” (2006) 在我国近海的急剧增强和减弱过程进行数值模拟研究, 模式较好地再现了台风的路径和强度变化; 通过地形敏感性试验, 着重研究了地形对近海台风强度变化的影响。结果表明: (1) “桑美” 强度变化与南亚高压、 副热带高压的强度变化呈反相变化关系, 当南亚高压和副热带高压减弱时, 台风急剧增强; 台风中心附近对流层高层辐散的增强导致 “桑美” 急剧增强, 对流层中低层辐散的增强以及中层辐合的增大与 “桑美” 的减弱密切相关; 来自海洋的暖湿气流是 “桑美” 发展的关键条件; 低层气旋性涡旋并入台风环流是 “桑美” 近海急剧增强的重要原因。 (2) 凝结加热过程对 “桑美” 的近海维持和发展增强非常重要, 尤其是对流层中上层凝结潜热的突然增强有利于台风在近海的急剧增强。 (3) 小范围地形对 “桑美” 在近海的强度和路径有一定影响, 但作用相对较小, 而且主要表现在台风登陆前后; 大范围地形导致水平风场的非对称分布和台风中心附近垂直运动的异常, 最终影响到台风的强度变化。     

POTENTIAL VORTICITY STRUCTURE OF SUMMER CYCLONES OVER THE CHANGJIANG-HUAIHE VALLEY*

Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical profiles of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After discussing a possible mechanism for the genesis and development of such systems and their differences from typical extratropical cyclones,a conceptual model for their activities is proposed:A weak disturbance in the midlevel of troposphere originated from around the Qinghai-Xizang Plateau may cause heavy precipitation under favourable conditions and latent heat release in the mid-troposphere leads to downward extension of cyclonic circulation and a wave on the quasi-stationary front.This weak cyclone can develop substantially and become a typical extratropical cyclone only when air from the lower stratosphere flows downslope along isentropic surfaces into the region of interest.     

东北冷涡的结构及其演变特征的个例综合分析

利用NCEP再分析资料、FY-2C、CloudSat云探测卫星和实况观测等资料对2009年6月27—30日出现的东北冷涡的热力动力结构、三维流场和云系演变特征进行了分析,并初步探讨了冷涡的发生、发展机理。结果表明:该冷涡冷心结构最初始于高层,随后逐渐向下伸展。成熟阶段的冷涡,对流层整层为冷心结构,冷中心位于对流层中高层,其上即平流层低层为暖心结构,中心东西两侧上升气流随高度向外倾斜,经向风趋于对称。发展初期温度槽落后于高度槽,且轴线向西倾斜,斜压性特征明显;至成熟阶段,温度中心与高度中心趋于重合,轴线近于竖直,显示出正压的特征;到减弱阶段,由于低层偏北风减弱明显,轴线又略向西倾斜。冷涡云带的产生与低层辐合带密切相关。CloudSat云探测卫星资料分析结果表明,冷涡环流内多中小尺度对流云团发展,且分布极不均匀。此次个例的研究结果揭示出冷涡的形成和发展跟对流层中上层切断低压的生成发展与对应的地面低压逐步耦合的动力学过程紧密相关,其中,冷暖气流呈旋转式下沉和上升,在冷涡中心形成偶极;对流层高层的干冷空气总是沿着等熵面从高层穿越等压面向下侵入到冷涡中心附近,干侵入使冷涡加强发展并维持其冷心结构。干侵入机制实际就是高位涡的侵入和下传,对预报冷涡的发展演变具有重要指示意义。     

POTENTIAL VORTICITY STRUCTURE OF SUMMER CYCLONES OVER THE CHANGJIANG-HUAIHE VALLEY

Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro-files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.Afterdiscussing a possible mechanism for the genesis and development of such systems and their differences fromtypical extratropical cyclones,a conceptual model for their activities is proposed:A weak disturbance in the mid-level of troposphere originated from around the Qinghai-Xizang Plateau may cause heavy precipitation underfavourable conditions and latent heat release in the mid-troposphere leads to downward extension of cycloniccirculation and a wave on the quasi-stationary front.This weak cyclone can develop substantially and becomea typical extratropical cyclone only when air from the lower stratosphere flows downslope along isentropic sur-faces into the region of interest.     

Analysis of Isentropic Potential Vorticity for a Strong Cold Wave During 2004/2005 Winter

Using the NCAR/NCEP daily reanalysis data from 1 December 2004 to 28 February 2005, the isentropic potential vorticity （IPV） analysis of a strong cold wave from 22 December 2004 to 1 January 2005 was made. It is found that the strong cold air of the cold wave originated from the lower stratosphere and upper troposphere of the high latitude in the Eurasian continent and the Arctic area. Before the outbreak of the cold wave, the strong cold air of high PV propagated down to the south of Lake Baikal, and was cut off by a low PV air of low latitude origin, forming a dipole-type circulation pattern with the low PV center （blocking high） in the northern Eurasian continent and the high PV one （low vortex） in the southern part. Along with decaying of the low PV center, the high PV center （strong cold air） moved towards the southeast along the northern flank of the Tibetan Plateau. When it arrived in East China, the air column of high PV rapidly stretched downward, leading to increase in its cyclonic vorticity, which made the East Asian major trough to deepen rapidly, and finally induced the outbreak of the cold wave. Further analysis indicates that in the southward and downward propagation process of the high PV center, the air flow west and north of the high PV center on isentropic surface subsided along the isentropic surface, resulting in rapid development of Siberian high, finally leading to the southward outbreak of the strong cold wave.     

等熵位涡在一次淮河流域大暴雨分析中的应用

利用NCEP/NCAR 1°×1°逐日再分析资料、常规气象观测资料,通过等熵位涡理论对淮河流域2009年9月24—25日的大暴雨过程进行分析。结果表明:淮河流域对流层低层的中尺度低涡的发生发展与此次暴雨密切相关;315 K等熵位涡高值中心的移动和强度变化很好地反映出中尺度低涡系统的发展变化情况,其移动方向与雨带走向一致,降水落区主要位于等熵位涡高值中心轴线移动方向右侧的强西南气流处,对应于345 K等熵面上干冷空气移动方向前部的暖湿区内;在暴雨发展强盛时期,淮河流域暴雨区上空从对流层高层至低层均存在明显的正等熵位涡平流,干冷空气的侵入使得低涡加强发展,辐合上升运动增强,有利于暴雨的增幅,这是引发此次暴雨过程重要的触发机制。     

一个干侵入参数及其应用

鉴于干侵入在气旋的爆发性发展、冷锋的演变等方面起着重要的促进作用,因此,文章详细分析了一次北方暴雨中的干侵入特征.分析发现,干侵入在此次降水事件中一直维持,而且降水随干侵入的增强而加强,干侵入推动了降水区的东南向移动.在McNulty早期工作的基础上,借鉴Doswell以及Schultz等发展的IM(ingredients-based methodology)方法,将其应用于干侵入的研究.文章将过去对干侵入(无论在等压面还足等熵面上)的研究中,用低相对湿度、冷平流、高位涡来表征干侵入气流的这些单个物理量综合起来,用一个简单、使用方便的物理参数来表征干侵入.这是以往暴雨研究巾的IM理论方法在干侵入研究领域的新尝试.文章朋新的干侵人参数,在等熵面上分析了实际降水过程中干侵入的演变.分析表明,干侵入参数能够较好地量化干侵入强度,指示卫星云图和水汽图像上干区的演变.通过等熵面与相应气压层的对比分析,发现等熵和等压面上的分析比较一致,等熵面上的干侵入在高层比低层强度大.由垂直剖面图的分析可见,干侵入气流位于低层暖湿气流上方,这就使得垂直方向上出现位势不稳定,有利于降水发生.这样,我们就可以通过干侵入参数来找干侵入区,关注干侵入区附近的不稳定区.来对降水做出预测,从而提高降水预报的准确率.     

2018年一次非典型梅雨锋暴雨过程诊断分析

利用常规地面气象观测资料、NCEP/NCAR FNL 1°×1°网格点逐6 h再分析资料,对2018年6月20日浙江省一次暴雨过程的主要环流系统、等熵位涡、垂直螺旋度等进行了天气动力学诊断分析。结果表明：850 hPa低涡切变、对流层中层冷空气、200 hPa南亚高压、副热带高压是此次暴雨过程发生的主要影响系统;700 hPa上的正垂直螺旋度中心对暴雨的发生有良好的指示意义;等熵位涡的演变和形态对冷空气活动有较好的视踪作用,等熵位涡中心两侧气流辐合,有利于低压系统发展,高层等熵位涡与冷空气活动有较好的对应关系,等熵位涡大值区偏南侧的移动与强降水落区有较好的对应关系。     

DIAGNOSTIC ANALYSIS OF THE RE-INTENSIFICATION OF HIGOS IN SOUTHERN CHINA AFTER LANDFALL

The NCEP Global Data Assimilation System analysis of grid data, satellite products of Naval Research Laboratory, conventional meteorological data and observations of automatic weather stations in Guangdong province were used together with environmental conditions, atmospheric circulation, and physical characteristics to diagnose the cause and mechanism of the intensification of tropical cyclone Higos in Southern China. The results showed that favorable environmental conditions of high temperature, humidity of the underlying surface, strong upper divergence, weak vertical wind shear, and the persistence of a southwest jet stream beside the southern Higos were the necessary ingredients that contributed to the maintenance of intensity and re-intensification of Higos. The sinking intrusion of cold air from the lower troposphere was the critical condition for its intensification over land. The frontal genesis caused by weak cold air increased the lower tropospheric convergence and updraft, and the condensation latent heat released by heavy rains promoted convergence. From this positive feedback process, Higos obtained an increasing of positive vorticity and re-intensified over land. The re-intensification was due not only to the build-up of wind and the reduction of pressure but also to the simultaneous warm-up of its warm core.     

地形影响蒙古气旋发展的观测和模拟研究

针对2001年4月上旬一次蒙古气旋发展过程中的地形因素进行了观测和模拟研究, 结果表明:依据低层冷空气是否越过阿尔泰—萨彦岭山地产生气旋冷锋, 蒙古气旋的发生发展过程可以划分为触发和发展两个阶段。在气旋的发展阶段, 斜压不稳定是其主要强迫机制。伴随地形对低层冷空气阻滞程度的变化, 蒙古气旋经历了从缓慢发展到剧烈加强的过程。阿尔泰—萨彦岭山地通过对低层冷空气的阻滞使山地上空等熵面更为陡立, 加强了对流层低层的斜压强迫, 从而使斜压强迫的涡度增长向低层聚集, 导致气旋发展强度增强。阿尔泰—萨彦岭山地及其南侧形成的峡谷地形对低空急流的位置、范围、强度及演变过程具有较重要影响。另外, 对流层高层位涡平流也是气旋发展的一个强迫因素, 但其影响较小。     

“海棠”台风(2005)暴雨过程数值模拟及位涡分析

采用WRF模式对2005年"海棠"台风登陆福建省前后24h内所造成的降水过程进行了数值模拟,在此基础上,利用模式输出结果,借助位涡理论分析位涡与台风低压流场及降水的关系,并结合对风场、相当位温、相对湿度等诊断量的分布特征分析,探讨了台风强降水的发展和维持机制。结果表明,310K等熵面上高位涡发展演变较好反映了台风低压系统路径移动以及强度变化的过程。暴雨中心主要出现在位涡大值区及其偏东北方向,且位涡气块回旋少动,与暴雨的发展维持密切相关。高位涡区主要位于等熵面坡度和梯度最大处,当等熵面上下贯通,对流层高层的高位涡沿等熵面下传,形成位涡柱时,有利于暴雨增幅。台风环流内水汽充足,上升运动强烈,也有助于此次台风降水强度持续强大。     

导致一例强沙尘暴的若干天气因素的观测和模拟研究

利用常规观测资料和数值模拟方法对 2 0 0 1年 4月 6～ 8日由蒙古气旋强烈发展触发的内蒙古地区强沙尘暴天气过程进行了分析研究。结果表明 :在这次“锋面气旋型”沙尘暴过程中 ,气旋冷锋是该天气系统引发沙尘暴的主要因素 ,冷锋过境对沙尘暴的触发作用远强于气旋发展。影响沙尘暴的天气因素中 ,地面大风形成主要源于气旋发展和锋后强冷平流 ,高空动量的有效下传则是另一重要原因。高空急流加强及其形成的次级环流使高空动量下传到对流层中层 ,其下方形成深厚混合层使这一动量继续下传到地面 ,是高空动量有效下传的机制。“混合层”可以从本质上反映有利沙尘暴形成的大气层结特征 ,其强度和高度很大程度决定沙尘暴的强弱。这次过程深厚混合层的形成是深厚干对流和强沙尘暴产生的主要原因。而它的形成则是长时间地面加热的结果 ,这也是特强沙尘暴仅发生在内蒙古中部偏北地区而不是下垫面条件更为适宜的内蒙古西部的原因。混合层空气的平流作用对内蒙古中部偏北地区深厚混合层的形成具有相当的贡献 ,其作用程度与地形分布密切相关。地面热通量试验证明地面加热不仅对冷锋过境产生的上升运动强度具有直接影响 ,也影响混合层形成和高空动量下传 ,并因此影响沙尘暴强度。     

干冷空气侵入在2005年12月山东半岛持续性降雪中的作用

利用常规资料和NCEP再分析资料分析了2005年12月山东半岛持续强降雪事件发生的环流背景及干冷空气活动特征,并运用湿位涡和锋生理论,研究了干冷空气在降雪事件中的作用.分析表明:低层湿度场的演变可以很好地反映山东半岛地区降雪的变化,但降雪事件与高层干冷空气紧密相连.对流层高层高位涡区与相对湿度小值区相对应,干空气主要来源于北侧(高纬度)对流层高层.高位涡区与低湿区都向下向南伸展,与低层MPV1<0的湿对称不稳定区对应.强降雪是低层饱和湿空气受地形强迫、锋生强迫的抬升作用及湿对称不稳定能量释放的共同作用造成的,而干冷空气的侵入是锋生和不稳定能量释放的触发机制.     

FORMATION AND STRUCTURAL EVOLUTION OF INITIAL DISTURBANCE OF TYPHOON FUNG-WONG (2008)

The formation of a tropical cyclone is the result of a process in which an initial disturbance evolves into a warm-core low-pressure system; however, the origin of the initial disturbance and the features of the initial fields are overlooked in most existing theories. In this study, based on FY-2C brightness temperature data and the Japan reanalysis dataset, the origin and evolution of the tropical disturbance that became Typhoon Fung-Wong (2008) were examined. The results demonstrated that the initial disturbance emerged within a saddle-type field with large vertical tropospheric wind shear. The vertical wind shear decreased with the adjustment of the upper circulation; moreover, accompanied by convection over the warm section around the upper cold vortex, it provided favorable thermal and dynamic conditions for the development of a tropical vortex. During its development, the zone of associated positive relative vorticity strengthened and descended from the mid-troposphere to lower levels. This rapid strengthening of lower-level vorticity was due to increasing convergence related to the intensification of the pressure gradient southwest of the subtropical high. This indicated that the upper cold vortex and West Pacific subtropical high played very important roles in this case.