用红外和水汽两个通道的卫星测值指定云迹风的高度

提出了一种改进的用红外和水汽两个通道的测值指定云迹风高度的算法。利用红外水汽散点图和云迹风本身自动地将有低云的目标区、有半透明卷云的目标区、有密蔽高云的目标区分开。在有低云的目标区和有密蔽高云的目标区用红外一个通道指定云高。在有半透明卷云的目标区用红外和水汽两个通道指定云高。在用两个通道的测值指定云高时，假定卷云高度以上不存在水汽，以红外和水汽两个通道亮温相同这个方程与两个通道辐射测值线性相关的方程联立解出云的高度     

Geoeffectiveness of magnetic cloud, shock/sheath, interaction region, high-speed stream and their combined occurrence

A subset of CMEs, called interplanetary magnetic clouds (MCs), are observed to have systematic rotation [northward to southward (NS) or southward to northward (SN)] in their field structures. These MCs identified in the heliospheric plasma and field data at 1 AU may have different features associated with them. These structures (NS/SN) may be isolated MC moving with the ambient solar wind. MCs (NS/SN) may also be associated with shock/sheath region, formed due to compression of the ambient plasma/field ahead of them. A fraction from each of these four types of MCs have additional features, being ‘pushed’ by fast solar wind streams from coronal holes, forming interaction region (IR) between MCs and high-speed solar wind streams (HSS). Using these different sets of MCs, we have done a detailed study of the geoeffectiveness of NS and SN turning MCs and their associated features (shock/sheath, IR and HSS). To study the process that produces the geomagnetic disturbances and influences its amplitude/duration, we have utilized the interplanetary plasma and field parameters, namely, plasma velocity, density, temperature, pressure, field strength and its north-south component, during the passage of these structures with different associated properties. Differences in the geoeffectiveness of MCs with different structural and dynamical properties have been identified. The possible role of high-speed stream in influencing the recovery time (and hence duration) of geomagnetic disturbance has also been investigated. A best-fit equation representing the relation between level of the geomagnetic activity (due to MCs) and interplanetary plasma/field parameter has been obtained.     

基于PS-VF-TBD的地波雷达船只目标航迹起始方法

针对地波雷达低信噪比目标信号"闪烁"导致的航迹起始困难问题,本文提出了一种基于PS-VF-TBD的航迹起始方法.该方法综合利用了地波雷达回波谱中目标信号的展宽特征和运动特性,利用PS-VF-TBD方法对运动目标能量有效积累的特点,提高对疑似目标多帧信号间的关联概率,进而提高对真实目标的搜索概率和航迹起始成功率.通过地波...     

Optical properties of a vertically inhomogeneous mid-latitude mid-level mixed-phase altocumulus in the infrared region

A vertically inhomogeneous mid-latitude mixed-phase altocumulus cloud was observed around 17:26 UTC on Oct. 14, 2001 during the 9th Cloud Layer Experiment (CLEX9). In this study the microphysical and optical properties of this cloud are investigated on the basis of in-situ observed vertical profiles of particle size and habit distributions. Two cloud models, assuming that the cloud properties were vertically homogeneous and inhomogeneous, are adopted to derive the bulk optical and radiative properties of this cloud. The observed microphysical properties are combined with the theoretical solutions to the scattering and absorption properties of individual cloud particles to determine the bulk optical properties at various heights within the cloud layer. The single-scattering properties of spherical liquid water droplets and nonspherical ice crystals are obtained from the Lorenz–Mie theory and an existing database, respectively. The bulk microphysical and optical properties associated with the inhomogeneous model depend strongly on the height above the cloud-base whereas the dependence is smoothed out in the case of the homogeneous model. Furthermore, the transfer of infrared radiation is simulated in conjunction with the two cloud models. It is shown that the brightness temperatures at the top of the atmosphere in the case of the homogeneous model can be 1.5% (3.8 K) higher than their counterpart associated with the inhomogeneous cloud model. This result demonstrates that the effect of the vertical inhomogeneity of a mixed-phase cloud on its radiative properties is not negligible.     

对云滴凝结增长方程的质疑

基于多元体系化学势和相平衡原理,分析认为“水蒸气凝结释放的潜热既升高了云滴表面温度,又向外传导热量”的观点违反了热力学第二定律,指出这样热传导过程是不可能进行的,分析认为大气中水蒸气凝结只能以辐射形式释放潜热。     

机载微波辐射计反演云液水含量的云物理方法

用一维层状云模式产生云样本,通过统计回归求得机载对空微波辐射计测云中路径积分液态水含量的反演系数,与用历史探空统计资料作相对湿度诊断产生云样本的反演方法进行了比较,并通过因素分析、数值模拟检验等方法对机载微波辐射计的探测误差进行估计。对2001年7月8日的个例分析表明,用云模式得到的统计样本,由于加入了对层状云物理过程的考虑,较为符合当天的实际天气情况,在一定程度上减小了由于背景大气条件、云温、云内含水量的垂直分布等的不确定性所引起的反演误差。对反演精度的数值模拟检验表明,各高度层的均方根相对误差在9.5%～12.7%之间,反演精度在所有高度上都高于原方法。对探测误差的因素分析表明,与仪器漂移及背景场引起的误差相比,由云液水垂直分布的不确定所引起的误差是不可忽略的。因此为进一步提高反演精度,根据实际宏观观测资料,对云模式产生的大量样本进行筛选,从中选取与实际云况较为符合的云样本进行拟合,结果表明,采用这一措施可以使反演精度得到进一步改善。     

利用多普勒天气雷达估算对流云火箭增雨防雹用弹量的方案

利用新一代多普勒天气雷达产品资料,结合人工影响天气原理,引用人工影响天气数值实验的人工冰核浓度等有关参数,将垂直累积液态含水量(VIL)及回波顶高度(ET)等导出产品合理地应用于火箭增雨防雹作业用弹量计算公式中,解决了以前人为或间接估计对流云作业区体积及其含水量的难题,提出客观定量计算人工增雨防雹作业用弹量的初步方案,并以其计算的用弹量为主要参数设计火箭作业参数指挥界面.经2005年一次增雨作业应用检验,证明结果切实可行,对节约人工影响天气成本,有效指导对流云火箭增雨防雹作业具有一定的意义.     

“7·18”济南突发性大暴雨特征

运用FY-2号气象卫星资料、NCEP再分析资料、常规资料以及自动站加密观测资料,对2007年7月18日济南市突发性大暴雨天气过程的形成发展进行了综合分析。结果显示:这次大暴雨发生在大气层结十分不稳定和高、低空急流耦合的有利大尺度环流背景下,由强烈发展的中尺度对流云团直接造成,具有明显的中尺度特征。低层冷空气南侵,触发了具有高不稳定能量的对流发展;低空强劲的西南急流直抵黄河下游一带,不仅与南下的冷空气形成强烈辐合,还将大量水汽和能量输送到该地区,使降水得以加强。     

A CLIMATOLOGY OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

Based on best-track data and JRA-25 reanalysis, a climatology of western North Pacific extratropical transition (ET) of tropical cyclone (TC) is presented in this paper. It was found that 35% (318 out of 912) of all TCs underwent ET during 1979–2008. The warm-season (June through September) ETs account for 64% of all ET events with the most occurrence in September. The area 120°E–150°E and 20°N–40°N is the most favorable region for ET onsets in western North Pacific. The TCs experience ET at latitudes 30°N–40°N and have the greatest intensity in contrast to other latitude bands. The distribution of ET onset locations shows obviously meridional migration in different seasons. A cyclone phase space (CPS) method was used to analyze the TC evolution during ET. Except for some cases of abnormal ET at relatively high latitudes, typical phase evolution paths—along which TC firstly showed thermal asymmetry and an upper-level cold core and then lost its low-level warm core—can be used to describe the main features of ET processes in western North Pacific. Some seasonal variations of ET evolution paths in CPS were also found at low latitudes south of 15°N, which suggests different ET onset mechanisms there. Further composite analysis concluded that warm-season ETs have generally two types of evolutions, but only one type in cold season (October through next May). The first type of warm-season ETs has less baroclinicity due to long distance between the TC and upper-level mid-latitude system. However, significant interactions between a mid-latitude upper -level trough and TC, of either approaching or being absorbed into the trough, and TC’s relations with downstream and upstream upper-level jets, are the fingerprints for both a second type of warm-season ETs and almost all the cold-season ETs. For each type of ETs, detailed structural characteristics as well as precipitation distribution are illustrated by latitude.     

基于人工神经网络的热带气旋路径预报试验

利用气候持续性因子,分别采用神经网络法及最小二乘回归法,建立西北太平洋地区12、24、36和48h热带气旋路径预报模型。通过对1992～2002年资料的试报,人工神经网络方法优于回归方法,且这种优势在预报时效较长时更明显。人工神经网络法48h的预报平均绝对误差比回归法减小27．56km,预报水平提高7％。