THE CCA BETWEEN 500 hPa GEOPOTENTIAL HEIGHT FIELDS OVER NORTHERN HEMISPHERE AND RAINFALL OF CHINA IN MAY

~~THE CCA BETWEEN 500 hPa GEOPOTENTIAL HEIGHT FIELDS OVER NORTHERN HEMISPHERE AND RAINFALL OF CHINA IN MAY@严华生$Department of Earth Sciences, Yunnan University, Kunming 650091 China @陈艳$Yunnan Meteorological Science Institute, Kunming 650034 China @郭世昌$Department of Earth Sciences, Yunnan University, Kunming 650091 China @王会军$Institute of Atmospheric Physics, Academy of Sciences, Beijing 100091 China~~ Project "973" (G1998040905)…     

Geopotential Reconstruction,Decomposition, Fast Computation,and Noise Cancellation by Harmonic Wavelets

Harmonic wavelets are introduced within the framework of the Sobolev-like Hilbert space H of potentials with square-integrable restrictions to the Earth's (mean) sphere _R . Basic tool is the construction of H-product kernels in terms of an (outer harmonics) orthonormal basis in H. Scaling function and wavelet are defined by means of so-called H-product kernels. Harmonic wavelets are shown to be building blocks that decorrelate geopotential data. A pyramid scheme enables fast computations. Multiscale signal-to-noise thresholding provides suitable denoising. Multiscale modelling of the Earth's anomalous potential from EGM96-model data is illustrated by use of bandlimited harmonic wavelets, i.e. Shannon and CP-wavelets.     

不同高程系统的比较

Geopotential, dynamic, orthometric and normal height systems and the corrections related to these systems are evaluated in this paper. Along two different routes, with a length of about 5 kilometers, precise leveling and gravity measurements are done. One of the routes is in an even field while the other is in a rough field. The magnitudes of orthometric, normal and dynamic corrections are calculated for each route. Orthometric, dynamic, and normal height differences are acquired by adding the corrections to the height differences obtained from geometric leveling. The magnitudes of the corrections between the two routes are compared. In addition, by subtracting orthometric, dynamic, and normal heights from geometric leveling, deviations of these heights from geometric leveling are counted.     

半球月平均位势高度场的若干环流指数及其变化特征

给出了表征半球月平均位势高度场性质的若干环流指数：气候场强度Ic、气候异常场平均强度Ia、气候场不稳定度Ius。用NCEP／NCAR40a再分析月平均位势高度场资料作了计算和分析，结果表明，这些环流指数存在清晰的时空结构和北、南半球差异，它们概括地给出了地球大气位势高度场气候及其异常的基本特点。     

The Propagation of Wave Packets and Its Relationship with the Subtropical Jet over Southern China in January 2008

The propagation of wave packets and its relationship with the subtropical jet was investigated for the period 26-29 January 2008 over southern China using ECMWF Interim re-analysis data.Wave packets propagated from the north to the south side of an upper front with eastward development along the upper front during this period.Due to the eastward development of propagation,the acceleration of geostrophic westerly winds shifted eastward along the front.There were two primary sources of the propagation of wave packets at around 30 N.The first was the temperature inversion layer below 500 hPa,and the second was baroclinic zones located along the polarward flank of the subtropical jet in the middle and upper troposphere.Most wave packets propagated horizontally from the baroclinic zones and then converged on the zero meridional gradients of zonal winds.     

华南冬季异常冷月预测概念模型I--500hPa高度场和海温场特征

确定了近45年华南冬季异常冷月出现的时间,分析了其同期至前期6个月500hPa位势高度场和海沮场的特征。各异常冷月当月500hPa高度场有相似的特征,亚洲-太平洋地区高度场的特征是北高南低,经向环流发展。给出了前期500hPa高度场差异显著月的距平特征。华南冬季各异常冷月至其前期6个月海温距平分布有持续性的特征,1月及其前期1～6个月赤道东太平洋ssT星El Nino特征,2月和12月呈La Nina特征。     

集合样本数影响月平均500 hPa高度场预测技巧分析

气候系统模式输出结果是当前开展气候预测业务的重要参考依据之一,如何提高气候系统模式输出结果的可信度是改进气候业务预测能力的关键之一。利用1999—2010年NCEP CFSv2模式每日四次预测未来45天的回算数据,分析了集合样本数对模式预测能力的影响。分析结果表明,模式对月平均500 hPa位势高度的预测技巧在热带地区较高,而中高纬度地区较低;模式对500 hPa位势高度时间异常的预测能力优于空间异常。无论是空间异常还是时间异常,随着模式超前时间的增加,预测技巧均逐渐降低,但是在不同区域和不同月份,模式预测技巧随超前时间的变化存在差异。此外,模式预测技巧存在非常大的年际变率。增加集合样本数,对不同月份和不同起报时间预测技巧的稳定度和预测技巧值均有明显正效果,特别是对亚洲中纬度地区改善度较大。增加集合样本数也可以在一定程度上降低模式预测技巧年际变率。集合样本数增加对于500 hPa位势高度空间异常的改进优于时间异常。      

华南前汛期降水与500hPa高度场耦合关系特征

利用NCEP／NCAR提供的1950～1999年4～6月逐日再分析资料,通过奇异值分解、子波变换等方法分析了华南前汛期降水与500hPa位势高度场耦合关系的多时间尺度特征。结果表明：华南前汛期降水和500hPa位势高度场相互耦合的空间分布型、季节内变化存在明显的年际差异,具有多层次、多时间尺度特征;华南前汛期降水和高度场耦合相关型许多一致的年际、年代际周期表明两者长期变化的耦合关系密切;另外,两者的年代际突变都十分显著。     

冬季北半球风暴轴能量演变的个例分析

利用观测资料,从扰动能量变化方程出发,通过分析能量的逐日演变过程,对风暴轴的各种内部因素在其维持中的作用进行了详细探讨。结果发现,涡动非地转位热能量所引起的“下游发展效应”是风暴轴得以在一常定区域维持的重要因素。     

北太平洋风暴轴“深冬抑制”现象的能量分析

采用欧洲中期天气预报中心逐日再分析资料（ERA-40）,从局地能量变化方程出发,通过分析北太平洋风暴轴区域对流层不同层次局地能量的季节演变过程,对风暴轴区域各能量项在“深冬抑制”现象中的作用进行了深入探讨。结果表明,天气尺度扰动动能的季节变化可以很好地反映北太平洋风暴轴的“深冬抑制”现象,并且该现象在对流层上层最为显著,其发生概率约为80％,其中20世纪70年代中后期到80年代前期抑制最强。从同期各能量项的变化来看,扰动动能的变化主要受斜压能量转换项、涡动非地转位势通量的散度项和正压能量转换项的影响。在深冬季节,由于消耗扰动动能的正压能量转换项虽有些微弱减少从而使得扰动动能有所增加,但为风暴轴提供扰动动能的斜压能量转换项和涡动非地转位势通量的散度项减少的幅度却更大,因而总的效果是扰动动能大为减小,这可能是造成北太平洋风暴轴“深冬抑制”现象的直接原因。