延安地区近５０年气候变化的特征分析

摘要：通过对１９５７—２００５年延安地区气温、降水及相对湿度的变化特征分析,揭示了近５０ａ来延安气候变化特征,结果表明：延安地区平均气温具有明显的年变化趋势,总体呈线性上升趋势,趋势率为０.２４２℃/（１０ａ）,１９８６年发生明显跃变,跃变后春季增温明显;降水量年变化特征趋势不明显,趋势变化较平均气温复杂,波动性大,２１世纪以来降水量有所增加。总体上２０世纪９０年代后呈现减少趋势。在全球气候变暖的大背景下,延安地区降水量下降,气温升高,气候变化有暖干化发展的趋势。

     

HⅢ(2n)中元素的一种标准化表示

给出HⅢ(2n)中元素的一种标准化表示,HⅢ(2n)={Z∈C^2n×2n|1/2(Z+Z'')>0,ZJ=JZ''},J=0 I_n-I_n 0,1/2(Z+Z)>0表示矩阵1/2(Z+z'')是正定的。     

A STUDY ON TYPHOON MOVEMENT PART Ⅰ:THE EFFECT OF DIABATIC HEATING AND HORIZONTAL TEMPERATURE DISTRIBUTION

A basic equation governing the movement of a typhoon has been derived based on the system of primitive equations of motion in the atmosphere. The role of several forcing factors which cause the deviation of the typhoon from the steering current have been discussed based on the governing equation. What is presented in Part Ⅰ is a theoretical analysis on the effects of diabatic heating and the horizontal temperature distribution. It is shown that the accelerations of a typhoon caused by diabatic heating and temperature advection coincide with the direction of the volume-averaged "diabatic steering velocity" QV and the "steering velocity of temperature advection" A_TV (V is the air velocity,Q the diabatic heating rate and A_T the temperature advection ), respectively. The precipitation (or condensation heating) on the right (left) side of a typhoon will accelerate (decelerate) the typhoon. The precipitation in the front (rear ) of the typhoon will turn it to the left (right) of its ordainal path. A typhoon will speed up (slow down) when it moves towards a region of cold (warm) air.     

PROBLEMS EXISTING IN THE VERTICAL DISCRETIZATION OF THE HYDROSTATIC EQUATION AND IMPROVEMENT TESTS

Through analysis and numerical computation of ECMWF's discrete scheme of hydrostatic equation(Baede et al.1979),it has been found that in the case of equal △σ there exist systematic errors in the scheme.The error E_Φ caused by taking the arithmetic mean of the geopotential heights of two adjacent half σ-levels as the geopotential height of the corresponding integer σ-level,increases with height and has an unacceptable maximum in the vicinity of the top of the atmosphere;however,the errors caused by the temperature treatment are generally small.On the other hand,if an uneven △σ-scheme in which the levels in the upper and lower atmosphere are denser than those in the middle atmosphere,is adopted,then E_Φ can be much reduced.However,if the resolution of the original equal Art-scheme doubles,then E_Φ can only be found to be much reduced in the troposphere and that in the vicinity of the atmospheric top is still unacceptable.Two numerical schemes for improvement have been presented. Of them one is the same as the ECMWF's scheme,but with equal △lnσ,and the other is to integrate the equation by the use of Tschebyscheff polynomials T_n and to adopt the zeros of T_N as the atmospheric levels where N is the total number of levels.The results show that with both schemes the computational errors can be much reduced,especially the latter,due to the fact that the errors of three statistical types are generally less than the root mean square error of the geopotential heights reported in TEMP.     

A STUDY ON DEFORMATIONS OF RAY AND ITS RELEVANT FACTORS*

In this paper,the effects of first and second meridional derivative(i.e.h_s^u,d²f/dy²,u″)of the Coriolis parameter,Westerly profile and topography structure on ray routes are qualitatively analysed by use of a simplified mathematical model.The analysis indicates that the second derivatives of the above relevant factors play an important role in the formation of great circle route.A profile of west wind similar to the real atmosphere may result in a "sine wave pattern" of ray.The effects of west wind shear,β factor and the slope of topography on the scale of radius of great circle,critical latitude of rays ard the amplitude of wave train of teleconnection are also discussed.Additionally,the characters of critical velocity profile for meridionally trapped wave are mentioned.     

大气垂直运动廓线特征及其与云和辐射的关联性分析：以CMIP6三个模式为例

基于第六次耦合模式比较计划(CMIP6)的3个全球气候模式结果,利用经验正交分解方法和参数方法分析了模式模拟的热带地区大尺度大气垂直运动廓线特征并揭示其与云和辐射量的关系。结果表明,基于EOF分解方法,3个模式均可较好地再现热带大气垂直运动特征,即热带大气垂直运动90%以上的方差可由两个主导的垂直结构模态解释,其中EOF1表征大气的整体上升或下沉,EOF2表征一个由深厚的中层辐合辐散占主导的垂直运动廓线。在此基础上定义了一对更为简洁易用的参数(ω和dω),此对参数可较好地描述EOF分解所揭示出的垂直运动廓线特征。利用新定义的参数发现,在西太平洋暖池区域,高云在"上重"下沉区域为低值,中云云量在"下重"上升运动区域为高值。大气层顶对外长波短波辐射均表现出对运动廓线结构的依赖。研究为评估气候模式对云和辐射模拟提供了一组有效因子。