沙尘天气过程起沙特征的观测试验和参数化研究进展

沙尘天气过程研究中,起沙过程是沙尘传输和沉降的基础,沙尘模式中的起沙参数化方案决定了能否准确模拟和预报沙尘天气。试验观测和数值模拟是研究起沙过程的重要途径。基于风蚀起沙的物理机制,总结了起沙机制和起沙特征的研究成果,介绍了风蚀起沙的主要影响因子,回顾了起沙关键参数（临界起沙摩擦速度（u*t ）或临界起沙风速（Ut ）、水平跃移沙尘通量（Q）和起沙通量（F））的试验观测及其沙尘模式应用中的参数化方案,并讨论了不同起沙参数化方案的应用与校验。同时,针对目前研究中存在的问题和今后可能的研究方向提出建议。     

VTI介质初至波多参数走时反演敏感核分析及反演策略

利用地震初至波走时信息建立近地表模型是地震勘探的关键步骤.由于近地表模型普遍呈现各向异性特征, 常规的各向同性近地表建模无法满足地震数据近地表校正和地下成像的需要, 因此, 发展各向异性介质的初至波走时多参数反演方法具有重要的理论意义和实际应用价值.本文基于Fomel群速(慢)度近似公式, 推导得到了声波VTI介质中16种参数化模式的走时多参数反演敏感核的解析解, 并详细分析了4种参数化模式下多参数敏感核随角度的变化特征.通过分析多参数的敏感核和多参数之间的耦合效应, 提出了在全方位和地表两种观测方式下最优的参数化方式和有效的多参数反演策略, 并通过理论分析和模型试验, 证明了所提出的反演策略的合理性和正确性.

     

论全球地震面波层析成像的参数化与样条插值模型

本文的参数化方法考虑不完全依赖数据分布的基函数的构造方法。借助函极小问题与样条插值问题的密切联系,得到了样条函数形式的参数化方法,即样条插值模型,样条插值模型是著名的Ｂａｃｋｕｓ－Ｇｉｌｂｅｒｔ模型在球面情形的推广。     

随机物理倾向扰动在风暴尺度集合预报中的影响研究

为深入探究随机物理倾向扰动（Stochastically Perturbed Parameterization Tendencies,SPPT）方案在风暴尺度集合预报中的影响,基于WRF模式利用FNL资料对SPPT方案中的3个参量分别进行敏感性试验,得到SPPT方案的最佳参数配置,并在此基础上分析SPPT方案模拟的降水分布特征。结果表明:SPPT方案敏感性试验中,去相关时间选择6 h时构造的集合成员可信度更高,逐时降水评分效果在积分中后期较高,对于暴雨及以上量级的评分技巧最优;造成降水主要天气系统的维持时间对该变量的选取有较大的影响。去相关空间尺度选择100 km的集合试验更为可靠,对降水预报技巧较高;同时该变量的选取与天气过程中的大尺度信息、中小尺度系统的活跃以及模式的空间分辨率有密切联系。通过对离散度和离群值分析认为扰动振幅选择0.525最为合理。SPPT方案集合成员在局部地区可以较大幅度地改变降水量,对降水落区的准确模拟存在一定的局限性。      

Application of a Large-Eddy Simulation Database to Optimisation of First-Order Closures for Neutral and Stably Stratified Boundary Layers

Large-eddy simulation (LES) is a well-established numerical technique, resolving the most energetic turbulent fluctuations in the planetary boundary layer. By averaging these fluctuations, high-quality profiles of mean quantities and turbulence statistics can be obtained in experiments with well-defined initial and boundary conditions. Hence, LES data can be beneficial for assessment and optimisation of turbulence closure schemes. A database of 80 LES runs (DATABASE64) for neutral and stably stratified planetary boundary layers (PBLs) is applied in this study to optimize first-order turbulence closure (FOC). Approximations for the mixing length scale and stability correction functions have been made to minimise a relative root-mean-square error over the entire database. New stability functions have correct asymptotes describing regimes of strong and weak mixing found in theoretical approaches, atmospheric observations and LES. The correct asymptotes exclude the need for a critical Richardson number in the FOC formulation. Further, we analysed the FOC quality as functions of the integral PBL stability and the vertical model resolution. We show that the FOC is never perfect because the turbulence in the upper half of the PBL is not generated by the local vertical gradients. Accordingly, the parameterised and LES-based fluxes decorrelate in the upper PBL. With this imperfection in mind, we show that there is no systematic quality deterioration of the FOC in the strongly stable PBL provided that the vertical model resolution is better than 10 levels within the PBL. In agreement with previous studies, we found that the quality improves slowly with the vertical resolution refinement, though it is generally wise not to overstretch the mesh in the lowest 500 m of the atmosphere where the observed, simulated and theoretically predicted stably stratified PBL is mostly located. The submission to a special issue of the “Boundary-Layer Meteorology” devoted to the NATO advanced research workshop “Atmospheric Boundary Layers: Modelling and Applications for Environmental Security”.     

青藏高原边界层高度特征对大气环流动力学效应的数值试验

利用NCAR的全球气候模式 (CCM3) 及第二次青藏高原边界层观测试验的研究结果, 对青藏高原上大气边界层高度的作用进行了研究, 分析了夏季青藏高原地区与长江流域上空的环流状况。研究表明:青藏高原的边界层高度特征对高原东南部地区以及长江流域出现强烈的垂直上升运动及其低层辐合、高层辐散存在着显著的动力效应, 深厚的高原边界层特征将使长江流域夏季区域性的云量及降水明显增加, 河套地区与黄河流域的夏季云量及降水有所减少。     

改进的物理过程参数化对台风路径数值预报的影响

文章介绍了国家气象中心的台风路径数值预报试验模式和新开发的改进物理过程参数化方案，对1992年的5个台风个例初步试验结果表明:改进物理过程参数化模式对台风路径和台风强度的预报比简单物理过程模式有明显提高，24 h和48 h台风中心位置预报误差分别为188 km和337 km，比原模式减小38 km和190 km；48 h台风中心气压与实况之差平均减小3 hPa。     

Melt Pond Scheme Parameter Estimation Using an Adjoint Model

Melt ponds significantly affect Arctic sea ice thermodynamic processes. The melt pond parameterization scheme in the Los Alamos sea ice model(CICE6.0) can predict the volume, area fraction(the ratio between melt pond area to sea ice area in a model grid), and depth of melt ponds. However, this scheme has some uncertain parameters that affect melt pond simulations. These parameters could be determined through a conventional parameter estimation method, which requires a large number of sensitivity simulations. The adjoint model can calculate the parameter sensitivity efficiently. In the present research, an adjoint model was developed for the CESM(Community Earth System Model) melt pond scheme. A melt pond parameter estimation algorithm was then developed based on the CICE6.0 sea ice model, melt pond adjoint model,and L-BFGS(Limited-memory Broyden-Fletcher-Goldfard-Shanno) minimization algorithm. The parameter estimation algorithm was verified under idealized conditions. By using MODIS(Moderate Resolution Imaging Spectroradiometer)melt pond fraction observation as a constraint and the developed parameter estimation algorithm, the melt pond aspect ratio parameter in CESM scheme, which is defined as the ratio between pond depth and pond area fraction, was estimated every eight days during summertime for two different regions in the Arctic. One region was covered by multi-year ice(MYI) and the other by first-year ice(FYI). The estimated parameter was then used in simulations and the results show that:(1) the estimated parameter varies over time and is quite different for MYI and FYI;(2) the estimated parameter improved the simulation of the melt pond fraction.     

云粒子谱演化研究中的一些问题

简略介绍了描述云中水凝物粒子群尺度谱演变的方法：谱函数方法和分档方法,并给出了分档模式实例。讨论了谱参数本身以及在应用中应注意的问题。分析了两类方法的对比研究的结果指出,一些重要的云降水物理过程,如粒子类型间的转化,涉及粒子运动状态和人工播撒的效应等过程,应当用分档方法来处理。