共查询到20条相似文献，搜索用时 140 毫秒
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对我国高空气象观测业务中的平均风计算方法及其存在的问题进行了分析和探讨,提出了完全采用矢量平均风算法来求取高空规定层风的业务流程改进方案;用锡林浩特站和阳江站同球施放的RS92GPS探空仪与L波段雷达-GTS1探空仪的对比观测数据集,对20~200s时间窗口下的各种矢量平均风计算方案及其规定风层计算结果进行了分析比对,提出未来改进的L波段高空气象观测系统可以测试使用时间窗口为30~45s的矢量平均风、使得计算风层达到每150~350m高程一个,以便进一步提高与GPS测风结果的一致性、更好地满足预报服务部门对高空风垂直分辨率的应用需求。 相似文献
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多普勒天气雷达VAD（Velocity Azimuth Display）风廓线资料可以提供高时间分辨率的高空风场信息。本文针对中国雷达VAD风廓线资料，设计发展了面向资料同化应用的NMIC（国家气象信息中心）质量控制方案，该方案改进了NCEP（国家环境预报中心）方案中存在的问题。利用2020年2—8月的L波段秒级探空风场资料，分别对比质量控制前、经过NCEP质量控制方案、以及经过NMIC质量控制方案的VAD风廓线资料，统计分析结果表明经过NMIC质量控制方案的VAD风廓线资料最接近观测，准确度最高，并且在各个高度上其偏差和均方根误差最小，充分说明了NMIC质量控制方案的有效性。相对背景场偏差分析表明，经过NMIC质量控制方案的VAD资料偏差和均方根误差最小，与背景场的偏差更接近高斯分布，更能满足资料同化的要求。本文的研究有助于推进VAD风廓线资料在数值预报科研和业务中的应用。 相似文献
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环境风垂直切变小大对台风强度变化有显著影响。通过查阅文献和会议交流发现,由于算法上的细微区别,导致同一个台风在计算环境风垂直切变时结果有所不同,有时差异较大。本研究针对这一问题,以南海快速增强台风为例,利用中国气象局整编的热带气旋年鉴、NCEP FNL、个例数值模拟资料等,计算并对比分析了南海台风在快速增强阶段不同环境风垂直切变计算方案和数据对计算结果的影响,并对业务应用时应该注意的问题展开讨论。 相似文献
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将非平衡风分成两部分:(1)非平街风的旋度部分(?)′_R和(2)非平衡风的散度部分(?)′_D。在产生暴雨的次天气尺度系统中,这两种非平衡风具有同样重要的作用。所以在有限区域细网格模式的初值化中,不能只考虑散度风,即使用通常称为“散度初值化”的方案,而且要考虑非平衡风的旋度部分。根据散度方程分析,(?)′_R是维持、调整散度场的重要因子。试验了三种风场初值化方案,结果表明,在风场初值中同时考虑(?)′_R和(?)′_D,可以明显改善模式的降水预报。 相似文献
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基于WRF预报模式、WRFDA Hybrid集合变分同化系统和ETKF方法,构建了面向城市气象观测网数据的快速更新混合同化系统。针对北京地区地基微波辐射计和风廓线雷达组网观测资料数据同化,开展了静态背景误差调整因子(特征长度尺度因子和方差因子)、局地化距离和集合权重系数4个重要参数敏感性试验研究。试验结果表明：当温度、相对湿度、u风和v风的特征长度尺度因子和方差因子分别调整为0.7/1.0、1.0/1.0、0.7/1.0和0.7/1.0,局地化距离和集合权重系数分别调整为11.2 km和0.5时,快速更新混合同化系统的分析场均方根误差最小。为对比三种常用同化方案,开展了默认参数混合同化、最优参数混合同化、三维变分同化对比试验,试验结果表明：在针对北京地区地基微波辐射计和风廓线雷达组网观测资料的快速更新同化预报试验中,混合同化方案表现优于三维变分,同时相对于默认参数混合同化方案,最优参数混合同化方案的风场、温度及湿度的分析场和预报场得到了进一步改善：风温湿的分析场均方根误差分别最大降低了13%、19%和5%,12～24 h预报场的均方根误差分别最大降低了2%、12%和5%。 相似文献
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垂直探测雷达的降水云分类方法在北京地区的应用 总被引：3，自引：0，他引：3
风廓线雷达采用相干累积技术提高雷达探测灵敏度,用于对降水云体进行垂直探测,能获取高分辨率的云体返回信号的全谱信息。利用多年降水天气统计资料,针对北京延庆地区降水特征,提出了基于风廓线雷达谱参数(回波强度、速度和谱宽)的降水云分类方案。该方案将降水资料分为浅对流、浅层状云、深对流、深层状云、混合—排除和混合—包含等六种降水类型。根据该方案,利用风廓线雷达结合双偏振雷达和自动雨量站观测资料,对2012年9月1日和2013年6月27日发生在延庆地区的两次降水天气过程进行了分析。结果表明,风廓线雷达谱参数垂直廓线可以较好的描述降水云体的垂直结构,回波强度廓线发展趋势与地面降水量趋势吻合较好。当降水存在对流时,地面降水量出现明显增大,同时伴随着大速度值区和高空大谱宽值区。利用基于风廓线雷达的分类方案识别降水云,可以降低降水类型误判的几率。 相似文献
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利用2014—2018年辽宁省探空资料分析了水平风速的垂直风廓线分布特征。用2座代表性测风塔逐时梯度风观测分析了采用不同高度组合方案计算出风切变指数的月、日变化特征, 分别用月、小时、年风切变指数推算高层风速和风功率密度, 并与实测对比。结果表明: 沈阳相较于大连地区风速随高度增加较快, 180 m高度以上风速基本保持不变, 而大连因其纬度低且靠近海洋, 300 m以下风速均匀上升。在非复杂地形情况下, 距地面10 m高度以上间隔一定高度设立4层风观测, 基本可以满足近地层风资源评估需求。受太阳辐射、下垫面、海陆热力性质差异等影响, 辽宁省风切变指数日变化特征比月变化更显著。利用小时风切变指数推算高层风速和风功率密度的方案优于采用月、年风切变指数方案。风切变指数日变化越显著, 采用逐时风切变指数推算方案越优于其他计算方案。 相似文献
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该文在GRAPES (Global/Regional Assimilation and PrEdiction System) 模式面三维变分 (3D_Var) 框架中引入了一种描述不同控制变量之间动力平衡约束的新方案。新方案采用统计得到的流函数和模式气压变量 ( π ) 之间的回归系数代替原方案中的线性平衡方程,来表达旋转风和质量场之间的平衡关系;采用流函数和势函数之间的回归系数,补充表达了原方案中所没有的旋转风和散度风之间的平衡关系。与原方案相比,新方案算法简单,避免了垂直方向的反复插值,减少了插值误差的引入。通过随机扰动试验和单点试验可以发现,在地转关系成立较好的区域,新方案中旋转风和质量场的耦合程度与原方案接近一致;而在地转关系不适用区域,新方案可以有效减小两者的耦合程度。此外,由于新方案中添加了旋转风和散度风之间的动力平衡约束,边界层的风场分析也更加接近大气真实状况。 相似文献
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Summary A land-air parametrization scheme (LAPS) describes mass, energy and momentum transfer between the land surface and the atmosphere. The scheme is designed as a software package which can be run as part of an atmospheric model or a stand-alone scheme. A single layer approach is chosen for the physical and biophysical scheme background. The scheme has six prognostic variables: two temperatures (one for the canopy vegetation and one for soil surface), one interception storage, and three soil moisture storage variables. The scheme's upper boundary conditions are: air temperature, water vapour pressure, wind speed, radiation and precipitation at some reference level within the atmospheric boundary layer. The sensible and latent heat are calculated using resistance representation. The evaporation from the bare soil is parametrized using the scheme. The soil part is designed as a three-layer model which is used to describe the vertical transfer of water in the soil.The performances of the LAPS scheme were tested using the results of meteorological measurements over a maize field at the experimental site De Sinderhoeve (The Netherlands). The predicted partitioning of the absorbed radiation into sensible and latent heat fluxes is in good agreement with observations. Also, the predicted leaf temperature agrees quite well with the observed values.With 9 Figures 相似文献
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Summary We construct the generalized inverse of a global numerical weather prediction (NWP) model, in order to prepare initial conditions for the model at time t=0 hrs. The inverse finds a weighted, least-squares best-fit to the dynamics for –24<t<0, to the previous initial condition att=–24, and to data att=–24,t=–18,t=–12 andt=0. That is, the inverse is a weak-constraint, four-dimensional variational assimilation scheme. The best-fit is found by solving the nonlinear Euler-Lagrange (EL) equations which determine the local extrema of a penalty functional. The latter is quadratic in the dynamical, initial and data residuals. The EL equations are solved using iterated representer expansions. The technique yields optimal conditioning of the very large minimization problem, which has 109 hydrodynamical and thermodynamical variables defined on a 4-dimensional, space-time grid.In addition to introducing the inverse NWP model, we demonstrate it on a medium-sized problem, namely, a study of the impact of reprocessed cloud track wind observations (RCTWO) from the 1990 Tropical Cyclone Motion Experiment (TCM-90). The impact is assessed in terms of the improvement of forecasts in the South China Sea att=+48 hours. The calculation shows that the computations are manageable, the iteration scheme converges, and that the RCTWO have a beneficial impact. 相似文献
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Two sensitivity experiments, in which CO2 is doubled and sea-surface temperatures are enhanced, were carried out using a general circulation model to determine the influence of the convective parametrization on simulated climate change. In the first experiment, a non-penetrative layer-swapping convection scheme is used; in the second, a penetrative scheme is used. It is found that the penetrative scheme gives the greater upper tropospheric warming (over 4.5 K compared to 4 K) and the greater reduction in upper tropospheric cloud, consistent with recent CO2 sensitivity studies. However, there is a 0.7 Wm–2 greater increase in net downward radiation at the top of the atmosphere in the experiment with the non-penetrative scheme, implying a larger tropical warming which is inconsistent with recent CO2 studies. Other possible explanations for discrepancies between recent studies of the equilibrium climate response to increasing CO2 are considered and discussed. The changes in the atmospheric fluxes of heat and moisture from the tropical continents in the model with the penetrative scheme differ from those found using the non-penetrative scheme, and those in an equilibrium experiment using the penetrative scheme. Thus, changes in circulation may explain the apparent discrepancy in the current experiments, but prescribed sea-surface temperature experiments may not provide a reliable indication of a model's equilibrium climate sensitivity.
Offprint requests to: JFB Mitchell 相似文献
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Summary The design of adaptive observations strategies must account for the particular properties of the data assimilation method. A new adjoint sensitivity approach to the targeted observations problem is proposed in the context of four-dimensional variational data assimilation (4D-Var). The method is based on a periodic update of the adjoint sensitivity field that takes into account the interaction between time distributed adaptive and routine observations. Information provided by all previously located observations is used to identify best locations for new targeted observations. Adaptive observations at distinct instants in time are selected in a sequential manner such that the method is only suboptimal. The selection algorithm proceeds backward in time and requires only one additional adjoint model integration in the assimilation window. Therefore, the method is very efficient and is suitable for practical applications. A comparative performance analysis is presented using the traditional adjoint sensitivity method as well as the total energy singular vectors technique as alternative adaptive strategies. Numerical experiments are performed in the twin experiments framework using a two-dimensional global shallow water model in spherical coordinates and an explicit Turkel-Zwas discretization scheme. Data from a NASA 500mb analysis valid for 00Z 16 Mar 2001 6h obtained with the GEOS-3 model was used to specify the geopotential height at the initial time and the initial velocities were obtained from a geostrophic balance. Numerical results show that the new adaptive observations approach is a promising method for targeted observations and its implementation is feasible for large scale atmospheric models. 相似文献
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Summary We study the response of the land-surface to prescribed atmospheric forcing for 31 May 1978 at Cabauw, Netherlands, using the land-surface scheme from the Coupled Atmospheric boundary layer-Plant-Soil (CAPS) model. Results from model runs show realistic daytime surface fluxes are produced using a canopy conductance formulation derived from Cabauw data (for 1987, a different year), and un-tuned parameterizations of root density (near-uniform with depth) and soil heat flux (reduced thermal conductivity through vegetation). Sensitivity of model-calculated surface heat fluxes to initial values of soil moisture is also examined. Results of this study provide the land-surface base state for a coupled land–atmosphere modeling study. 相似文献
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Summary Most finite-difference numerical weather prediction models employ vertical discretizations that are staggered, and are low-order (usually second-order) approximations for the important terms such as the derivation of the geopotential from the hydrostatic equation, and the calculation of the vertically integrated divergence. In a sigma-coordinate model the latter is used for computing both the surface pressure change and the vertical velocity. All of the above-mentioned variables can diminish the accuracy of the forecast if they are not calculated accurately, and can have an impact on related quantities such as precipitation.In this study various discretization schemes in the vertical are compared both in theory and in practice. Four different vertical grids are tested: one unstaggered and three staggered (including the widely-used Lorenz grid). The comparison is carried out by assessing the accuracy of the grids using vertical numerics that range from second-order up to sixth-order.The theoretical part of the study examines how faithfully each vertical grid reproduces the vertical modes of the governing equations linearized with a basic state atmosphere. The performance of the grids is evaluated for 2nd, 4th and 6th-order numerical schemes based on Lagrange polynomials, and for a 6th-ordercompact scheme.Our interpretation of the results of the theoretical study is as follows. The most important result is that the order of accuracy employed in the numerics seems to be more significant than the choice of vertical grid. There are differences between the grids at second-order, but these differences effectively vanish as the order of accuracy increases. The sixth-order schemes all produce very accurate results with the grids performing equally well, and with the compact scheme significantly outperforming the Lagrange scheme. A second major result is that for the number of levels typically used in current operational forecast models, second-order schemes (which are used almost universally) all appear to be relatively poor, for other than the lowest modes.The theoretical claims were confirmed in practice using a large number (100) of forecasts with the Australian Bureau of Meteorology Research Centre's operational model. By comparing test model forecasts using the four grids and the different orders of numerics with very high resolution control model forecasts, the results of the theoretical study seem to be corroborated.With 8 Figures 相似文献
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Summary ¶A new E–l boundary layer scheme is tested within the U.S. Navys COAMPS model. The goal is to give COAMPS the capability to simulate mesoscale cellular convection. The new scheme is aimed to be consistent with both classic results for clear entrainment and recent calibrations, derived from large-eddy simulations, for entrainment into smoke clouds and water clouds. A parameter is included in the scheme that allows sub-grid transport to be reduced so that, when the model has 2km grid spacing or less, more of the transport is forced to occur in resolved convection. At 2km grid spacing, the scheme allows COAMPS to simulate the break up of a stratocumulus cloud deck into mesoscale cellular convection.Received June 7, 2002; accepted August 13, 2002
Published online: February 20, 2003 相似文献
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An acceleration scheme is proposed in a coupled ocean-atmosphere model for the simulation of long term climate evolutions forced by climate forcing of longer than millennia time scales. In this coordinated acceleration scheme, both the surface forcing and the deep ocean are accelerated simultaneously by the same factor. The acceleration scheme is evaluated in a 3-dimensional ocean general circulation model and in a coupled ocean-atmosphere model of intermediate complexity. For millennial climate evolution, our acceleration scheme produces reasonably good simulations with an acceleration factor of about 5. For climate evolution of even longer time scales, the acceleration factor can be increased further. 相似文献
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Ashok K. Luhar 《Boundary-Layer Meteorology》1998,88(1):103-120
Analytical parameterisations of the thermal internal boundary-layer (TIBL) height based on the slab approach are widely used in coastal dispersion models. However, they tend to a singular behaviour when the stability of the onshore flow is close to neutral. Assuming that convective turbulence dominates mixing, we derive a more general analytical model that is valid for both stable and neutral onshore flows. The model is based on the existing framework for the slab approach but involving the Zilitinkevich correction (or the spin-up term). The height variation of the onshore flow lapse rate is accounted for in the model by including an initial TIBL height. An algebraic form of the model also includes the mechanical mixing contribution to the TIBL growth and is, therefore, suitable for use when the overland surface heat flux is small and friction velocity large. The new analytical model is tested with field measurements taken under near-neutral onshore flow conditions. The performance of the model is shown to be better than a commonly used TIBL parameterisation scheme. 相似文献
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The scaling properties of the depth of the inner-layer of flow over low hills are studied by means of numerical solution of the equations. Two closure schemes are applied: the mixing-length model and the E- formulation. It is shown that the scale relation for the inner-layer depth lies between two formulations proposed in literature. It is also shown that the scale relation depends on the closure scheme.Presently at the European Centre for Medium-Range Weather Forecasts, Shinficld Park, Reading, Berkshire RG2 9AX, England. 相似文献