二维波状地形上的流场

本第一部分，在一个简化的二层模式中，求解大气波动方程，得到了二维波状起伏地形上扰动流线的分析解，研究在上、下两层大气中，不同的温度廓线和风速廓线情况下，地形引起扰动流场形式，同时讨论了支配扰动振幅的大气因子和地形特征。章第二部分，利用大气非静力方程组求出几种大气条件下流场扰动的数值解，并和分析解做了比较。     

晴空卫星红外模拟资料反演大气温度廓线的研究

HIRS／3资料的反演是一个典型的非适定问题,而奇异值分解法（SVD）是一种解病态线性代数方程组的有效方法,它在遇到矩阵的不适定问题时依然可以保持其数值稳定性并能尽量多地利用各探测通道的有效信息。将SVD方法应用于卫星资料的温度反演问题中可以将资料空间和参数空间分型,从中提取有效信息来反演大气温度廓线。通过理想资料试验,分析了温度廓线初猜值、水汽廓线误差等因素对温度反演结果的影响。结果表明：对HIRS／3资料来说,用SVD法反演大气温度廓线时只能截取一定的阶数,以取4～7为宜;温度廓线初猜值的选取对反演结果的影响较大,当模式层的中层误差较大时得到的反演结果最稳定;水汽廓线的扰动对中低层的温度反演结果和第5,8,10,11和16通道的亮温值有较大影响。     

东西风廓线特征与大气运动平衡态定常波的相关关系及共振条件的研究

本文采用简化数学模型探讨了东、西风廓线特征与外源强迫下大气环流平衡态定常波结构的相关关系。文中采用实际观测资料研究了西风廓线特征与大气环流型季节特征之间的联系。研究表明,西风廓线冬、夏季节差异与中、高纬度西风槽“冬三夏四”波数差气候特征有关,且低纬强东风切变可作为赤道东风波周期振荡成因之一。冬夏西风廓线季节特征可导致大地形强迫效应、海陆加热因子影响作用的显著季节差异。研究还揭示了大气环流型优势波转换的基流特征影响效应,并导出了流场与纬向加热强迫源共振状态的西风廓线特征函数与临界曲线。     

二维波状地形上的流场

在一个简化的二层模式中，求解大气波动方程，得到了二维波状起伏地形上扰动流线的分析解。研究了在上、下两层大气中，不同的温度廓线和风速廓线情况下，地形引起扰动的流场形式，同时讨论了支配扰动振幅的大气因子和地形特征。分析解的结果表明:若大气低层为深厚的不稳定层，地形引起的波动很微弱;如低层大气强稳定，上层大气弱稳定，则可能产生较强的波动;而当上层稳定度增加时，可产生非陷波，有利于高层动量下传，造成较大的地面风速。     

一种依据初始场构造的参考大气廓线及对高原地区预报的影响

地形追随坐标系下的动力学方程组通常都要引入参考大气的概念来减少气压梯度力的计算误差.参考大气的一般取法是满足静止和静力平衡关系,实际大气被看成在参考大气上的偏差.实际大气与参考大气越接近,它们之间的偏差就越小,计算就越精确.参考大气的取法一般有等温大气、定常温度廓线、初始资料进行水平平均的垂直温度廓线等.本文在一个非静力的中尺度模式中选取经过水平平均的初始温度场的垂直廓线构造模式的参考大气廓线.但是初始资料在三维空间是离散的,这里根据三次样条函数的分段连续光滑的性质,构造了随起报时间不同而不同的,只随高度变化的解析形式的参考大气廓线.构造的参考大气廓线完全满足静力平衡关系,方程中的静力平衡部分可以得到最大限度地扣除.试验表明,与等温大气相比,这种根据初始状态选取的参考大气和实际资料更接近,在大地形附近气压梯度力的计算误差更小,500 hPa高原附近的24 h气压预报更精确.     

全球大气温度廓线的统计特性分析

利用欧洲数值预报中心发布的第三代ERA-Interim月平均再分析资料对1979—2016年全球大气温度廓线进行统计,分别探讨了南、北半球大气温度廓线平均值和标准差随季节、纬度和海陆的时空分布特征,并与国内外常用的AFGL标准大气廓线进行了对比。研究结果表明:南、北半球各高度层温度的平均值、频数最大温度区间和最大值垂直分布均随高度先减小后增加;在大气低层,多年的温度波动较大,200 hPa处波动达到最小;不论是北半球还是南半球,大气温度平均值廓线均具有典型的纬度差异,其中低纬度季节性差异较小,中纬度次之,高纬季节性差异最大;各季节大气温度廓线的海陆差异不同,且南半球海陆差异比北半球大。大气温度标准差廓线同样存在纬度、海陆和季节分布差异。根据ECMWF再分析资料构建的温度廓线较AFGL标准大气廓线而言具有更加丰富的时空分布等细节特征,并且代表了气候变化后最新的大气温度状况。有关结果可作为现有标准大气廓线的更新和完善,为新型卫星仪器应用性能评估、辐射传输算法和大气反演方法评价和对比分析提供支持。      

发展中的地基大气廓线探测

最初的大气廓线探测—无线电探空的出现和组网观测推动了气象学的发展。地基遥感大气廓线探测的发展将会推动对中小尺度天气系统变化规律的认识,提高对强天气过程的认识和预报能力。地基遥感大气廓线探测的主体技术已经成熟,但其复杂性和应用难度,远高于无线电探空,在应用环节、设备研制生产环节和多种技术的综合集成方面都面对技术挑战。多种大气廓线探测技术综合集成已成为大气廓线探测发展的重要特征和趋势。综合集成一方面能够提供更多要素,以满足应用需求;另一方面将改进、完善大气廓线探测能力,提高探测精度。     

中性和不稳定层结大气的孤立行波精确解

通过研究二维准动量无辐散、无摩擦层结大气非线性方程组的行波解问题证明，非线性行波解的本质属性是由参数ｂ的符号性质决定的。当ｂ＞０时，为周期解，其周期与相应的线性周期解的周期相等；当ｂ≤０时，为孤立波解。给出了一般行波解的解析表达式。并细致地研究了中性和不稳定层结大气中的孤立行波的特征，发现中性和不稳定层结大气中存在具有类似于飑线结构特征的孤立波。指出了中性和不稳定层结大气中的一般孤立行波物理量的分布特征。     

应用ATOVS资料反演大气温湿廓线

本文用牛顿迭代的方法反演NOAA-15极轨气象卫星ATOVS资料，求解大气温度廓线和水汽廓线，本文利用一阶变分原理从辐射传输方程中得到了大气温度、水汽权重函数的解析形式，并改进了传统使用的线性迭代方法，利用牛顿非线性迭代方法求解大气表层温度，大气温度廓线及大气水汽廓线，并根据大气参量的自相关性，将大气温度廓线、大气水汽廓线用经验正交函数（EOF）的线性组合表示，减少了要反演的参数，提高了反演稳定性和迭代速度。     

绿洲与荒漠相互影响下大气边界层特征的模拟

用发展的二维中尺度土壤－植被－大气连续体数值模式模拟了绿洲与荒漠相互影响下的大气边界层特征。得到了绿洲和临近荒漠之间的边界层高度、风螺线、风速廓线、位温廓线和比湿廓线的差别,并给出了绿洲对其上游和下游荒漠大气的不同影响。基本再现了白天绿洲大气逆温和临近绿洲的荒漠大气逆湿。模拟实验研究不仅验证了外场观测结果,而且也使我们对复杂下垫面边界层结构有了一些新的认识。     

NWP模式中纬向平均环流系统误差的动力诊断

证明了模式在预报时段的纬向平均环流误差，是由于在预报时段内模式大气和真实大气中西风加速过程的不同造成的。又由于原始方程的无加速定理中各强迫因子具有良好的线性迭加性，因此能够清楚地将造成模式系统误差的动力因子分解开来。通过对Ｔ４２Ｌ９模式的分析，说明原始方程的无加速定理可以作为分析模式系统误差的良好手段。动力诊断分析结果表明，模式对纬向平均环流分布具有较好的预报能力，但在各缔带也存在明显的误差。通过无加速定理的分解分析，本文研究了这些误差的成因及改善模式的可能途径。     

DIAGNOSIS OF NWP SYSTEMATIC FORECAST ERRORS IN ZONAL MEAN CIRCULATION

It is proved in this paper that NWP systematic forecast errors in the zonal mean circulation aredue to the difference in westerly acceleration process during the forecasting period between model andreal atmospheres.Those forcing factors which evoke the zonal mean wind variation can be split into various linearterms according to the non-acceleration theorem in a primitive equation system,By applying this tech-nique to the diagnosis of the forecast produets of the T42L9 model in January 1992 and in July 1992,it is indicated that the model has the ability to forecast the zonal mean wind to a reasonable extent,but there are still some errors in several places,especially in the upper troposphere and lower strato-sphere in the mid-latitude region as well as near the surface.The results of analysis by employing thisscheme reveal the reason responsible for the systematic forecast errors of the zonal mean wind in themodel and the possible way of improving it.It is also shown that non-acceleration theorem can be used as an efficient tool to diagnose thephysical processes of NWP models.     

热带海气耦合Kelvin波的弱相互作用

本文在简单的热带海气耦合方程组中 ,引进基本风场和平均海流的作用以后 ,对热带海气耦合 Kelvin波的不稳定性进行了讨论 ,得到其耦合不稳定的判据条件 ,并且分析了它的传播结构特征。     

副热带对流层高层夏季准定常涡旋系统动力成因的初步探讨

本文采用一个高截断的斜压谱模式、探讨了在热力强迫作用下副热带夏季对流层高层准定常涡旋系统形成和维持的动力机制。模式中考虑了纬向不对称的热力强迫作用,带状流与波动分量之间的非线性相互作用以及随纬度而变的基本气流的共同影响,所得到的一类稳定平衡态的高层流场特征说明了上述准定常涡旋系统的一些主要特点,并进而讨论了热力强迫的控制作用等问题。     

用初始方程二层模式模拟一月和七月全球海平面气压场

用低分辨率的初始方程二层模式在给定下垫面温度下模拟了一月及七月全球海平面气压场,其中加热项主要是感热垂直输送。计算采用守恒的Lilly空间差分格式及Matsuno的时间差分格式。海平面气压的初值给成常数值,高空的风速及气温的初值给成纬向平均的气侯值。在数值模拟中,下垫面温度用一月及七月的气候实际值。计算的冬半球海平面气压与观测值相当一致,而夏半球的结果稍差些。本模式所求得的全球海平面气压场能与实况相比,结果并不差于高分辨率的复杂模式。     

EVALUATION OF SURFACE-LAYER WIND PROFILES WITH HEIFE OBSERVATIONS

In this paper the mean wind speed profiles in the atmospheric surfacelayer over oasis, sand, and Gobi desert surfaces in the HEIhe river FieldExperiment (HEIFE) area are discussed for various stability conditions. Themathematical representation of mean wind speed profiles obtained fromdifferent sources are used to estimate the mean wind speeds, and the resultsare compared with observed wind speed data obtained at 20 m meteorologicaltowers over different ground surfaces. It is found that for unstable and neutral conditions, a compositeexponential profile and flux-profile relationship can be used to describe thewind speed profile in the atmospheric surface layer over homogeneoussurfaces, the composite exponential profile giving a relatively high accuracyin the estimation of wind speed profiles. For stable conditions, thecomposite exponential profile also can be used to estimate the wind speedprofile, but for very stable conditions, the accuracy is not good. For thoseconditions, flux-profile equations can give estimates of the wind speedprofile with relatively high accuracy.     

全球资料分析中重力波的重要性

本文用哈佛(Hough)调和分析方法作全球(实测)资料的展开,发现重力波分量在风场和高度场的客观分析中是重要的。对全球范围内一些重要天气系统的描写若忽略重力波分量,则许多天气系统分析的强度就会明显偏弱,甚至分析不出来。低纬地区高、低压中心值偏弱4—8位势什米,中高纬地区也有较大的误差。含有重力波(一定分量)的风场的分析也比地转流函数的风场分析更合理,而且不零乱。 本文对按频率大小编号的重力波分量和涡旋波分量的截取项数,也提供了一些试验结果,似乎以分别取15和25项为宜。     

The MJO in an AGCM with three different cumulus parameterization schemes

The Madden–Julian oscillation (MJO) is simulated using an AGCM with three different cumulus parameterization schemes: a moist convective adjustment (MCA) scheme, the Zhang–McFarlane (ZM) mass-flux scheme, and the Tiedtke scheme. Results show that the simulated MJO is highly dependent on the cumulus parameterization used. Among the three cumulus parameterizations, only the MCA scheme produces MJO features similar to observations, including the reasonable spatial distribution, intraseasonal time scales and eastward propagation. Meanwhile, the amplitude is too large and the eastward propagation speed too fast than observations and the relationship between precipitation and low-level wind anomaly is unrealistic with enhanced convection occurring within easterly anomalies instead of westerly anomalies as in observations. The over-dependence of precipitation on boundary convergence produced by the MCA scheme is presumably responsible for this unrealistic phase relation in the simulation. The other two schemes produce very poor simulations of the MJO: spectral power of westward propagation is larger than that of eastward propagation in zonal wind and precipitation, indicating a westward propagation of the intraseasonal variability.The mean state and vertical profile of diabatic heating are perhaps responsible for the differences in these simulations. The MCA scheme produces relatively realistic climate background. When either ZM or Tiedtke scheme is used, the observed extension of westerly winds from the western Pacific to the dateline is missing and precipitation over the equatorial region and SPCZ is dramatically underestimated. In addition, diabatic heating produced by both ZM and Tiedtke schemes are very weak and nearly uniform with height. The heating profile produced by the MCA scheme has a middle-heavy structure with much larger magnitude than those produced by the other two schemes. In addition, a very unrealistic boundary layer heating maximum produced by the MCA scheme induces too strong surface convergence, which perhaps contributes to the too strong intraseasonal variability in the simulation.     

THE IMPACT OF A DIAGNOSTIC CLOUD SCHEME ON FORECASTS WITH A GLOBAL ATMOSPHERE MODEL

Experiments were conducted to test the impact of a cloud diagnosis scheme in place of prescribed zonalaverage cloud on medium and long range integrations with the Australian Bureau of Meteorology ResearchCentre(BMRC)global atmosphere model.The cloud scheme was shown to improve the temperature bias inthe lower troposphere but there was deterioration in the upper troposphere,especially in the tropics,asso-ciated with underestimation of high cloud amount.Thirty day mean fields in a January integration showed greater amplitude in the Northern Hemisphereplanetary waves and a deeper Antarctic circumpolar trough than the control experiment or a simulation withno cloud.The results for the diagnosed cloud case agree more closely with corresponding observed fields.There was also some reduction in the zonal average zonal wind component reflecting the additional zonalasymmetry introduced by the diagnostic cloud scheme.Similar trends were also noted in medium and longrange forecasts for January and July conditions,although the impact on predictive skill was slight and insome cases detrimental.Areas for improving the diagnostic cloud scheme are noted.     

Topographically forced three-wave quasi-esonant and non-resonant interactions among barotropic rossby waves on an infinnite beta-plane

In this paper, we first apply the assumption h = εh′ of topographic variation (h is the nondimensional topographic height and is a small parameter) to obtain nonlinear equations describing three-wave quasi-resonant and non-resonant interactions among Rossby waves for zonal wavenumbers 1—3 over a wavenumber-two bottom topography (WTBT). Some numerical calculations are made with the fourt-order Rung-Kutta Scheme. It is found that for the case without topographic forcing, the period of three-wave quasi-resonance (TWQR) is found to be independent of the zonal basic westerly wind, but dependent on the meridional wavenumber and the initial amplitudes. For the fixed initial data, when the frequency mismatch is smaller and the meridional wavelength is moderate, its period will belong to the 30–60-day period band. However, when the wavenumber-two topography is included, the periods of the forced quasi-resonant Rossby waves are also found to be strongly dependent on the setting of the zonal basic westerly wind. Under the same conditions, only when the zonal basic westerly wind reaches a moderate extent, intraseasonal oscillations in the 30–60-day period band can be found for zonal wavenumbers 1–3. On the other hand, if three Rossby waves considered have the same meridional wavenumber, three-wave non-resonant interaction over a WTBT can occur in this case. When the WTBT vanishes, the amplitudes of these Rossby waves are conserved. But in the presence of a WTBT, the three Rossby waves oscillate with the identical period. The period, over a moderate range of the zonal basic westerly wind, is in the intraseasonal, 30–60-Day range.