太行山东麓焚风天气的统计特征和机理分析Ⅱ:背风波对焚风产生和传播影响的个例分析

利用中尺度模式WRF3.3对太行山东麓焚风典型个例进行了数值模拟。结果表明,太行山东麓焚风的发生和移动与山脉背风波密切相关。由此建立了太行山东麓焚风的概念模型:西北或偏西气流途经山西盆地、山西境内的山脉或高原,再越过太行山,在其东麓形成背风波。背风波的下沉气流气温按干绝热方式上升,同时下沉气流也会对低层大气产生压缩增温效应,使得太行山东麓产生焚风。背风波即为重力波,可以伴随着下沉气流向下游移动,正变温区同时也向东移动。变温区移动的速度和重力波的传播速度相同。背风波的产生,需要Scorer数向上足够的减小,而且不连续,即要求大气是稳定的且存在明显的风速切变。     

一种对资源不稳定性敏感的EASY-backfill算法

利用合成技术对1995—2006年冬季（11月—次年2月）生成在西北太平洋上的34个热带气旋（tropicalcyclone,TC）个例进行分析,研究冬季西北太平洋TC生成的大尺度环流特征及其生成机制,结果表明：冬季TC生成的大尺度环流特征型为东风波西传型;北半球冬季对流层低层出现的跨赤道气旋对是冬季北半球TC形成的重要特征;太平洋中部赤道混合Rossby重力波西北传,与强对流中心重合,性质转为＂热带低压型扰动＂,为冬季热带气旋生成提供扰动源。对合成TC初始场的涡动扰动动能的收支分析表明,涡动有效位能和正压不稳定转换为TC形成提供了能量,这两种能量分别与积云对流加热和水平不均匀气流有关。正压不稳定能量转换为动能主要位于对流层中下层,而扰动有效位能的转换主要位于对流层中上层。低层热带东风波动从平均气流中获得正压不稳定能量,并与强积云对流耦合,热力和动力共同作用下形成TC。     

Precursory Signals of Extensive and Persistent Extreme Cold Events in China

The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.     

基于优化包络相关法的罗兰C天波延迟估计算法

针对低信噪比条件下,罗兰C天波信号延迟时间估计的准确性和有效性问题,提出基于优化包络的相关系数时域法。通过分析标准罗兰C信号包络的特征,分别采用微分和二次微分方法对罗兰C信号包络进行优化,形成陡峭的包络信号上升沿;利用相关系数法对接收信号包络和参考信号包络进行匹配,形成的匹配峰值分别对应地波和天波信号到达的时刻,由此可获得天波信号的延迟时间;通过仿真分析和实测信号试验验证,证明该方法能满足数字化接收机的实际要求,并具有更高的抗干扰能力、估计准确性和自动识别功能的特点。估计的结果还可以作为判别相位跟踪和周期识别正确率的辅助依据。     

遥感解译在南京市生活垃圾填埋场识别中的应用

运用遥感技术对南京市航空影像进行了解译工作,提取了面积大于10 000 m2的垃圾场位置并进行了实地查证和分析比对,绘制出南京市垃圾填埋场分布图,为南京市垃圾场的适宜性评价工作奠定了基础。     

Wave-dependence of friction velocity,roughness length,and drag coefficient over coastal and open water surfaces by using three databases

The parameterization of friction velocity, roughness length, and the drag coefficient over coastal zones and open water surfaces enables us to better understand the physical processes of air-water interaction. In context of measurements from the Humidity Exchange over the Sea Main Experiment (HEXMAX), we recently proposed wave-parameter dependent approaches to sea surface friction velocity and the aerodynamic roughness by using the dimensional analysis method. To extend the application of these approaches to a range of natural surface conditions, the present study is to assess this approach by using both coastal shallow (RASEX) and open water surface measurements (Lake Ontario and Grand Banks ERS-1 SAR) where wind speeds were greater than 6.44 m s^-1. Friction velocities, the surface aerodynamic roughness, and the neutral drag coefficient estimated by these approaches under moderate wind conditions were compared with the measurements mentioned above. Results showed that the coefficients in these approaches for coastal shallow water surface differ from those for open water surfaces, and that the aerodynamic roughness length in terms of wave age or significant wave height should be treated differently for coastal shallow and open water surfaces.     

Unstable Dynamical Properties of Spiral Cloud Bands in Tropical Cyclones

A nondivergent barotropic model （Model 1） and a barotropic primitive equation vortex model （Model 2） are linearized respectively in this paper. Then their perturbation wave spectrums are computed with a normal mode approach to study the instability problem on an appointed tropical cyclone （TC）-like vortex, thereby, the dynamic instability properties of spiral cloud bands of TCs are discussed. The results show that the unstable mode of both models exhibits a spiral band-like structure that propagates away from the vortex outside the radius of maximum winds. The discrete modal instability of the pure vortex Rossby wave can account for the generation of the eyewall and the inner spiral band. The unstable mode in Model 2 has three parts, i.e., eyewall, inner and outer spiral bands. This mode can be interpreted as a mixed vortex Rossby-inertia gravitational wave. The unbalanced property of the wave outside the stagnation radius of the vortex Rossby wave is one of the important reasons for the formation of the outer spiral band in TCs. Accordingly, the outer spiral band can be identified to possess properties of an inertial-gravitational wave. When the formation of unstable inner and outer spiral bands is studied, a barotropic vortex model shall be used. In this model, the most unstable perturbation bears the attributes of either the vortex Rossby wave or the inertial-gravitational wave, depending on the vortex radius. So such perturbations shall be viewed as an unbalanced and unstable mixed wave of these two kinds of waves.     

The Impact of Mid- and High-Latitude Rossby Wave Activities on the Medium-Range Evolution of the EAP Pattern During the Pre-Rainy Period of South China

Based on the NCEP DOE AMIP II daily reanalysis data (1979{2005), the evolution of the East Asia/Pacific(EAP) teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time scale. It is found that positive and negative EAP patterns share a similar generation process. In the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of the EAP pattern over East Asia. Among the three anomaly centers, the western Pacific subtropical center appears the latest. Rossby wave packets propagate from the high latitude anomaly center toward the mid-latitude and the subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the subtropical jet waveguide and the incoming Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanate from the subtropical Asia toward East Asia. Positive and negative EAP patterns could not be regarded as "mirrors" to each other with simply re- versed phase. For the positive pattern, the positive height anomaly center around the Scandinavia Peninsula keeps its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer mature time of the positive pattern. As for the formation of the negative EAP pattern, however, the incoming Rossby wave energy from the upstream contributes to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, the two anomlous circulations are evolved into the Northeast Asia and the mid-latitude anomaly centers of the negative pattern, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative pattern. During the pre-rainy period of South China, the prevalence of the EAP pattern signiˉcantly affects the rainfall over the region south of the Yangtze River. The positive (negative) EAP pattern tends to causepositive (negative) precipitation anomalies in that region. This is di?erent from the earlier research findingsbased on monthly mean data.     

影响广播中波转播站防雷系统作用的几个关键技术

电台中波转播站多建于城市近郊区,由于天线高耸落雷几率高,因而易受雷击干扰。针对建站时原已通过防雷验收的转播站设施在投入使用后依然频遭雷击受损的状况,分析了其防雷系统的内在布设技术问题,认为广播中波转播站原有防雷系统的一些关键技术缺漏是遭雷击受损的主要原因,并从转播站的实际情况出发,提出了转播站防雷设计的几个关键技术问题的解决方法：接地网逐级分流、屏蔽馈线再加设外屏蔽环群技术以及不同的线路、不同系统保护的配合方法等,从而形成广播转播站完整的防雷保护系统框架。