陆面过程模式CLASS径流模拟的改进和应用

针对陆面过程模式CLASS(Canadian Land Surface Scheme)产流模拟方面的不足,提出考虑壤中流产流机制的产流模拟方案。利用淮河流域能量和水分循环试验(HUBEX)资料,在史灌河流域对改进前后的模型进行了对比试验。结果表明,产流模拟改进方案大大提高了CLASS的径流模拟能力,同时改善了模式对土壤含水量的模拟。     

一些陆面要素非均匀分布对模式计算结果影响的理论分析

应用平均参数化方法,从理论上分别研究了地表温度、地面粗糙度、积雪深度和密度非均匀分布对相关物理量计算的影响。结果表明:考虑地表温度的非均匀分布影响后,模式网格上平均地面的长波辐射通量增加,地面饱和水汽压也增加;在相同的地表温度分布变差系数和常温情况下,与长波辐射通量相比,地面饱和水汽压的变化对地表温度非均匀分布较为敏感;地面粗糙度非均匀分布对地面中性曳力系数和BATS型地面积雪覆盖率有一定的影响;积雪深度和密度非均匀分布也对地面积雪覆盖率有一定的影响。     

陆面过程模式的改进及其检验

文中对陆面过程模式 (BATS)进行了改进 ,改进后的模式能较好地模拟地表物理量的年、季和日变化 ,它有两方面的特点 :采用热扩散方程模拟 7层土壤温度 ,模拟的温度可与实测值进行比较 ;在BATS的地表径流方案中 ,考虑了空间不均匀性的一般地表径流 (GVIC)过程 ,研究结果表明 :⑴模式能很好地模拟各层土壤温度的年、季和日变化。冬季土壤温度下层高于上层 ,而在夏季上层高于下层 ,这种上下层温度的转换时间大约在 4和 10月份 ,这与实测土壤温度的年变化非常一致。较为准确地模拟了各层土壤温度日变化的时滞效应。⑵用南京和武汉站的资料 ,将BATS地表径流方案模拟的地表水分分量与GVIC方案进行比较 ,BATS地表径流方案模拟的地表水分分量 ,与总水量的平衡相差较大 ,而GVIC模拟的效果相对较好 ,地表总水量基本上与降水总量达到了平衡     

中尺度模式质量控制源程存的改进

介绍NCAR/PSU中尺度大气数值模式质量控制的基本原理和技术方法,分析MM4质量控制源程序中存在的问题和不足,并进行优化改进,提高程序的质量控制功能。     

坡面辐射场的模式计算及结果分析

本文旨在建立一个不依靠地面辐射观测资料的坡面辐射场的计算模式。在全国范围内均匀地选取74个气象台站,计算了我国1、7月份8个坡向和8个坡度的坡面辐射平衡及其分量,并进行了分析,揭示了一些规律。     

大气模式中表面水热通量计算的一些问题

对现有的大气模式中计算海面和大气间水、热通量的通量-廓线关系式进行了评论,提出一个理论上较完整的通量-廓线关系式。其中考虑了水汽对M－O参数的影响,并引进相应于虚位温的标量粗糙度。MoanaWave的实测资料表明,由于该资料相应于温度的粗糙度zoh和湿度粗糙度zoq相差不大,使现有的公式计算结果与文中提出的公式差别不大。当zoh,zoq差别大时,两种公式结果有一定的差别。而文中公式理论上更为合理。还将不稳定状态下计算通量的简化方法推广到海面。     

坡面散射辐射的分布特征及其计算模式

本文应用安装在经纬仪上的天空辐射表所观测的坡面散射辐射资料,对散射辐射的各向异性问题作了较为详尽的分析。揭示出坡面散射辐射随坡向、坡度变化的基本规律。文中还对前人所提出的计算坡面散射辐射的各种模式进行了检验、评述。最终提出一种通用性较强的坡面散射辐射通量密度的计算模式。其物理意义和计算精度都较国外同类模式优越。     

清江和长江上游干支流域面雨量计算方法及其应用

将气象站点雨量以算术平均、加权平均两种算法所获得的面雨量,与稠密的水文站点雨量按算术平均计算得到的面雨量进行比较分析,得到了应用气象站资料计算长江上游不同干支流域及清江流域面雨量的最佳方案。     

丘陵地区面雨量计算方法及应用

根据高斯权重客观分析原理，在考虑了流域内各地的降水气候差异和地形分布特点的基础上，找出一种适合于丘陵地区的面雨量计算方法。并将该方法计算的面雨量与泰森多边形法进行比较，研究了这两种计算方法的优缺点；此外，还研究了面雨量与流域的洪涝灾害的关系。结果表明，两者关系非常密切，流域面雨量的变化能较好地反映未来洪水的变化趋势。     

计算稳定性的若干问题

偏微分方程的近似解法都是用一个有限个自由度的系统来代替原来的连续介质系统。在步长为有限值(而非无穷小)情况下的计算稳定性、计算紊乱及计算准确度问题是个有实际重要性问题。本文从物理方面入手讨论这些问题,指出计算紊乱现象或计算不稳定现象是由三种机理造成的:频散效应、能谱非线性转移效应及能量增长效应;指出利用能量守恒方程及正交展开法对于克服计算紊乱现象和提高计算准确度来说可能是较好的。还特别讨论了原始方程的计算困难问题,指出非线性项的计算误差常能激发出强烈的短波长的快波,这是造成计算紊乱的最重要方面。     

全天空成像仪云量计算方法的改进

全天空成像仪（total sky imager 440,TSI-440）可以实现白天全天空云量的持续自动监测,时空分辨率较高,得到的云量计算结果更精确.首先介绍了TSI-440的基本原理和资料格式,并基于太湖地区2008年5-10月的TSI-440资料及无锡站地面观测资料,采用统计方法详细地分析了不同天气情况下图像的成像特征及云量的计算误差.结果发现：图像的成像特征与能见度密切相关,红蓝比值随着能见度的减小而增大.另外,仪器在处理阴天图像及复杂天空（多云）图像时,易造成一定的云量计算误差.针对上述问题,本文通过直方图分析,重新选定了红蓝比阈值（晴空点阈值0.62,云点阈值0.66）,基于新阈值计算的云量结果较仪器自带的处理结果更为准确,减小了因天气状况不同而产生的云量计算误差.     

Some applications of a new,time-dependent cylinder ice accretion model

A new, time-dependent ice accretion model on a non-rotating cylinder is described briefly. In order to demonstrate the power and versatility of the model, we present some results related to anti-icing, marine icing and helicopter rotor-blade icing.The model results show that the initial cylinder temperature can have a significant effect on both the shape and the mass of the ice accretion. The thermal properties of the cylinder material are also shown to be important when internal conduction and convection from the un-iced downstream face of the cylinder are taken into account.     

Experiments on scalar dispersion within a model plant canopy part II: An elevated plane source

This paper describes a wind-tunnel experiment on the dispersion of trace heat from an effectively planar source within a model plant canopy, the source height being h _s = 0.80 h _c , where h _c is the canopy height. A sensor assembly consisting of three coplanar hot wires and one cold wire was used to make simultaneous measurements of the temperature and the streamwise and vertical velocity components. It was found that:

1. The thermal layer consisted of two parts with different length scales, an inner sublayer (scaling with h _s and h _c ) which quickly reached streamwise equilibrium downstream of the leading edge of the source, and an outer sublayer which was self-preserving with a length scale proportional to the depth of the thermal layer.
2. Below 2h _c , the vertical eddy diffusivity for heat from the plane source (K _HP ) was substantially less than the far-field limit of the corresponding diffusivity for heat from a lateral line source at the same height as the plane source. This shows that dispersion from plane or other distributed sources in canopies is influenced, near the canopy, by turbulence ‘memory’ and must be considered as a superposition of both near-field and far-field processes. Hence, one-dimensional models for scalar transport from distributed sources in canopies are wrong in principle, irrespective of the order of closure.
3. In the budgets for temperature variance, and for the vertical and streamwise components of the turbulent heat flux, turbulent transport was a major loss between h _s and h _c and a principal gain mechanism below h _s , as also observed in the budgets for turbulent energy and shear stress.
4. Quadrant analysis of the vertical heat flux showed that sweeps and ejections contributed about equal amounts to the heat flux between h _s and h _c , though among the more intense events, sweeps were dominant. Below h _s , almost all the heat was transported by sweeps.

     

Oceanic climatology in the coupled model FGOALS-g2: Improvements and biases

The present study examines simulated oceanic climatology in the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2) forced by historical external forcing data. The oceanic temperatures and circulations in FGOALS-g2 were found to be comparable to those observed, and substantially improved compared to those simulated by the previous version, FGOALS-g1.0. Compared with simulations by FGOALS-g1.0, the shallow mixed layer depths were better captured in the eastern Atlantic and Pacific Ocean in FGOALS-g2. In the high latitudes of the Northern Hemisphere, the cold biases of SST were about 1°C–5°C smaller in FGOALS-g2. The associated sea ice distributions and their seasonal cycles were more realistic in FGOALS-g2. The pattern of Atlantic Meridional Overturning Circulation (AMOC) was better simulated in FGOALS-g2, although its magnitude was larger than that found in observed data. The simulated Antarctic Circumpolar Current (ACC) transport was about 140 Sv through the Drake Passage, which is close to that observed. Moreover, Antarctic Intermediate Water (AAIW) was better captured in FGOALS-g2. However, large SST cold biases (>3°C) were still found to exist around major western boundary currents and in the Barents Sea, which can be explained by excessively strong oceanic cold advection and unresolved processes owing to the coarse resolution. In the Indo-Pacific warm pool, the cold biases were partly related to the excessive loss of heat from the ocean. Along the eastern coast in the Atlantic and Pacific Oceans, the warm biases were due to overestimation of shortwave radiation. In the Indian Ocean and Southern Ocean, the surface fresh biases were mainly due to the biases of precipitation. In the tropical Pacific Ocean, the surface fresh biases (>2 psu) were mainly caused by excessive precipitation and oceanic advection. In the Indo-Pacific Ocean, fresh biases were also found to dominate in the upper 1000 m, except in the northeastern Indian Ocean. There were warm and salty biases (3°C–4°C and 1–2 psu) from the surface to the bottom in the Labrador Sea, which might be due to large amounts of heat transport and excessive evaporation, respectively. For vertical structures, the maximal biases of temperature and salinity were found to be located at depths of >600 m in the Arctic Ocean, and their values exceeded 4°C and 2 psu, respectively.     

Improvements of the coupled WRF-Lake model over Lake Nam Co,Central Tibetan Plateau

A series of model sensitivity simulations are carried out to calibrate and improve the Weather Research and Forecasting Model coupled with a one-dimensional lake model (WRF-Lake) based on observations over Lake Nam Co. Using the default lake model parameters, the solution of WRF-Lake exhibits significant biases in both the lake thermodynamics and regional climatology, i.e., higher lake surface temperature (LST), earlier onset of summer thermal stratification, and overestimated near-surface air temperature and precipitation induced by the lake’s excessive warming and moistening impacts. The performance of WRF-Lake is improved through adjusting the initial lake temperature profile, the temperature of maximum water density (Tdmax), the surface roughness length, and the light extinction coefficient. Results show that initializing the water temperature with spring observation mitigates the LST overestimation and reduces the timing error of the onset of thermal stratification. By further adjusting Tdmax from 4 °C to the observed value of 3.5 °C, the LST increase from June to mid-July is enhanced and the buildup of thermal stratification is more accurately predicted. Through incorporating the parameterized surface roughness length and decreasing the light extinction coefficient, the model better reproduces the observed daily evolution of LST and vertical lake temperature profile. The calibrated WRF-Lake effectively mitigates the overestimation of over-lake air temperature at 2 m height and precipitation over regions downwind the lake. This suggests that an improved lake scheme within the coupled WRF-Lake is essential for realistically simulating the lake–air interactions and the regional climate over the lake-rich Tibetan Plateau.

     

Review of the development and applications of the Adem thermodynamic climate model

Recent advances in the development and applications of the author's Hemispheric Thermodynamic Climate Model are presented. The model has been adapted to simulate the climates from 18 kyr BP to the present, and to study the effect of the ice sheets, the insolation anomalies and the atmospheric CO₂ content on such climates. The surface ocean temperature anomaly is also simulated in the model, and comparison with values of CLIMAP (1981) for 18 kyr BP shows some agreement. A long series of numerical experiments have lead to the improvement in prediction of the monthly surface temperature anomalies. Verification of 93 predictions over the contiguous United States of America shows a useful skill in the predictions. The model is being adapted for forecasting in the Mexican Republic. Experiments to improve the skill in prediction of surface ocean temperature anomalies in the Northern Hemisphere have been carried out, and using a fine resolution grid, the model has been used to simulate the annual cycle of the normal sea surface temperatures in the Gulf of Mexico, that agrees well with observations.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

Improvements in the detection efficiency model for the Brazilian lightning detection network (BrasilDAT)

The detection efficiency (DE) is the most important performance gauge of a lightning detection network (LDN). Moreover, the main motivation for evaluating the DE of a LDN is to separate the geographical variations of the CG lightning parameters from the variations regarding the network performance. A review of previous relative DE techniques and simple methods to correct the cloud-to-ground (CG) lightning flash density maps is presented. In addition, recent improvements in the flash DE model for the Brazilian lightning detection network (BrasilDAT) are discussed. The DE estimated values are based on the sensor individual DE probability functions, which are derived from a large amount of CG stroke data provided by the network considering different distances from the sensor and specific peak current ranges. The new approach provides better results when compared with the previous developments, since the calculation of the sensor DE probability functions neglects the lightning data provided by the minimum number of reporting sensors. Hence it is possible to minimize the unrealistic enhancement of the DE closer to the network boundaries (“border effect”) without affecting significantly the performance inside the network. The main result is a more realistic correction of the CG flash density maps, particularly at the outermost network areas, leading to an improvement in the model sensitivity.     

A finite element-spherical harmonics model for radiative transfer in inhomogeneous clouds.: Part II. Some applications

EVENT has been used to examine the effects of 3D cloud structure, distribution, and inhomogeneity on the scattering of visible solar radiation and the resulting 3D radiation field. Large eddy simulation and aircraft measurements are used to create realistic cloud fields which are continuous or broken with smooth or uneven tops. The values, patterns and variance in the resulting downwelling and upwelling radiation from incident visible solar radiation at different angles are then examined and compared to measurements. The results from EVENT confirm that 3D cloud structure is important in determining the visible radiation field, and that these results are strongly influenced by the solar zenith angle. The results match those from other models using visible solar radiation, and are supported by aircraft measurements of visible radiation, providing confidence in the new model.