一阶弹性波交错网格时间高阶差分格式及稳定性分析

弹性波模拟或逆时偏移时,对空间偏导数采用高阶差分格式可提高计算精度,但这种算法的稳定性条件过于严格,要求差分离散的时间步长必须足够小以确保算法稳定。在常规空间高阶差分格式的基础上,将速度(应力)对时间的高阶导数转化为不同精度的应力(速度)对空间的差分,得到了一种新的基于交错网格的时间高阶、空间高阶差分格式。通过对交错网格时间高阶差分格式稳定性的分析,认为该算法的稳定性条件较常规算法宽松,在弹性波场的求解过程中可以采用更大的时间步长。     

长时效的正压原始方程能量完全守恒(拟)谱模式

遵循误差反演补偿新计算原理,对正压原始方程传统气象全球拟谱模式方案进行了改造,构造了正压原始方程能量完全守恒全球拟增模式新计算方案,解决了正压原始方程的(非线性)计算稳定性问题和能量守恒整体性质保持问题,改进了相应正压原始方程传统气象全球拟谱模式方案的计算效能。新方案的数值试验表明:在计算实践上,新方案在解决能量守恒问题的同时,可解决(非线性)计算稳定性问题,并在一定条件下可解决非线性计算收敛性问题。进一步的比较数值试验还表明:在计算实践上,新方案具有在提高相应传统气象方案的计算精度,减少其计算量的同时,延长其计算时效,解决其中一类特定“气候漂移”问题方面的效用。本工作原理也适用于斜压原始方程情形。     

雷达定量降水动态分级Z-I关系估算方法

利用高时空分辨率的雷达定量降水估测和预报(RQPE和RQPF)对洪水监测、发布洪水警报起重要指导作用，目前国内外对其研究的方法主要采用概率配对法、Z-I关系法和基于Z-I关系的数学算法校正法，这些方法均存在强调某一因素忽略其它因素的问题，并且对短时强降水，尤其是极强降水低估严重。从统计和个例两方面对比分析了四种雷达定量降水方法的误差，致力于寻找一种将雷达回波反射率预报场反演为降水场时误差较小的技术方法，能改进对短时强降水、特别是极强降水严重低估问题的方法，并且该方法也能在业务应用中方便、快速、精确实现。对比研究结果表明：动态分级Z-I关系法是一种对雷达QPE和回波反射率预报场反演降水场都较好的方法，并且改进了对短时强降水、尤其是大于55 mm/h的短时极强降水低估的问题；在业务计算中仅需15秒，能满足6分钟更新一次计算结果的需要，而且不依赖气候统计，便于移植。     

An improvement of the mass flux convection parameterization scheme and its sensitivity tests for seasonal prediction over China

A modified cumulus parameterization scheme, suitable for use in a seasonal forecast model, is presented. This parameterization scheme is an improvement of the mass flux convection scheme developed by Gregory and Rowntree (1989; 1990). This convection scheme uses a “bulk” cloud model to present an ensemble of convective clouds, and aims to represent shallow, deep, and mid-level convection. At present,this convection scheme is employed in the NCC T63L20 model (National Climate Center, China Meteorological Administration). Simulation results with this scheme have revealed some deficiencies in the scheme,although to some extent, it improves the accuracy of the simulation. In order to alleviate the deficiencies and reflect the effect of cumulus convection in the actual atmosphere, the scheme is modified and improved.The improvements include (i) the full estimation of the effects of the large-scale convergence in the lower layer upon cumulus convection, (ii) the revision of the initial convective mass flux, and (iii) the regulation of convective-scale downdrafts. A comparison of the results obtained by using the original model and the modified one shows that the improvement and modification of the original convection scheme is successful in simulating the precipitation and general circulation field, because the modified scheme provides a good simulation of the main features of seasonal precipitation in China, and an analysis of the anomaly correlation eoetfieient between the simulation and the observations confirms the improved results.     

High-order compact MacCormack scheme for two-dimensional compressible and non-hydrostatic equations of the atmosphere

This study is devoted to application of the fourth-order compact MacCormack scheme to spatial differencing of the conservative form of two-dimensional and non-hydrostatic equation of a dry atmosphere. To advance the solution in time a four-stage Runge–Kutta method is used. To perform the simulations, two test cases including evolution of a warm bubble and a cold bubble in a neutral atmosphere with open and rigid boundaries are employed. In addition, the second-order MacCormack and the standard fourth-order compact MacCormack schemes are used to perform the simulations. Qualitative and quantitative assessment of the numerical results for different test cases exhibit the superiority of the fourth-order compact MacCormack scheme on the second-order method.     

The numerical simulation on the PBL structure and its evolution over small-scale concave terrain

A high-resolution, nonhydrostatic, three-dimensional diagnostic PBL model over small-scale concave terrain was established in this paper. A two-dimensional prognostic model was developed based on the diagnostic model. The hydrostatic approximation was abandoned and the simple energy (E-ε) closure scheme was used in both mod-els. Using the two models, characteristics of PBL structure and its evolution were fully studied. The main characteris-tic of the PBL is the circulation, and it fairly affects the distribution of the pollutant in the pit.     

不同参数化方案对风预报效果影响个例研究

中尺度气象模式对风场的预报效果与参数化方案的适应性紧密相关.以内蒙古高原丘陵地形、江苏平缓的海陆交界地形2种典型下垫面试验风电场为模拟区域,分别用WRFV3.2 （Weather Research and Forecast Model）模式自带的6种物理过程参数化组合方案预报了2010年1月和7月两个风电场区域的风速和风向,对比分析了参数化组合方案差异对风场预报的影响.结果表明：①内蒙古试验区,边界层MRF方案描述的边界层结构较MYJ方案合理;微物理方案WSM3在夏季的风速预报能力优于WSM6,而冬季相反;复杂地形区域的风场预报需考虑陆面过程参数化方案,尤其是夏季降水发生后,陆面过程对于边界层结构的影响增大,选用Noah优于无陆面过程.②江苏试验区,边界层MRF方案描述的边界层结构较MYJ方案合理;1月陆面过程RUC方案优于陆面热量扩散和Noah;7月陆面热量扩散方案优于RUC和Noah.③风向预报6个方案的预报风向统计与实际记录风向统计有较好的一致性,风向概率分布相似,盛行风向一致且稳定.     

双参数云物理方案中谱形参数作用分析和数值模拟试验

云物理参数化方案中,各种粒子通常采用Г谱分布函数n(D)=N0Dαexp(-λD)。双参数方案中谱参数截距N0和斜率λ通过预报给出,谱形参数α设为固定值。为了讨论谱形参数的作用,理论上分析了谱形参数取值对沉降过程和微物理源汇项的影响。利用MM5模式中增加的双参数显式云物理方案模拟了西北地区一次层状云降水过程,模拟针对雨滴谱的谱形参数rα不同取值分别做了试验。模拟结果基本符合理论分析,谱形参数rα变化时模拟出的地面降水和云的宏微观特征有差异。     

国家气象中心NWP新资料归档系统的技术特征

文章简要介绍了“八五”以来,国家气象中心数值预报系统新的归档方案设计特点、意义、内容,并探讨了归档软件开发中的一系列技术问题。     

气候变暖对黑龙江省农作物结构调整影响及未来50年农业情景对策

在未来30、50年气温将增高1．9℃、2．4℃情景下,积温带向北推移近5个纬距,2050年,原第1积温带北移至大兴安岭北部,其余4个积温带基本消失。气候变暖将使黑龙江省主栽农作物水稻、小麦、玉米、大豆等种植区域和模式发生变化。因此提出了未来适应农业发展的6项对策,特别是主要作物结构调整及区域分布。