若干声雷达回波图象的分析

本文分析了近些年由声雷达观测到的海（陆）风、大风、下坡风和雾的回波图象和相应气象参数变化的特征。     

芬兰EO11型声雷达

声雷达是连续监测大气边界层的一种新手段。声雷达探测时,先发射声脉冲,再接收大气反射(散射)的回波。这种探测方法,是对常规仪器观测的重要补充,其优点有二:①可以进行连续监测,从而有可能探测短暂的天气现象,判别其发展动向;②建造和运转费用都较低。声雷达对监测下列气象现象特别有用:逆温层高度及其日变化;污染控制所需要的混合层深度;对流活动(热股流);边界层波;雾层厚度或低层云厚度。     

冬季兰州声雷达回波与天气系统的关系

本文分析了兰州1984年11月15—24日声雷达回波的形态特征及其与天气系统的关系。结果表明:声雷达回波所反映的稳定层和天气系统之间有较好的对应。无明显冷空气活动时,盛行低层逆温回波。受青藏高原地形影响,高原东北侧边界层中的流场和散度场有明显日变化,夜间在距地面300—600m处为准定常辐散层,由它引起的下沉增温作用是低层逆温形成的重要原因。冷锋过境后,低层逆温回波溃散。冷锋后(即高压前部)出现过类似对流泡状回波和纤维状的强风切变回波。     

利用测温声雷达回波图估算大气扩散的一种参数化方法

本文提出了一种基于湍流扩散统计理论的利用声雷达回波图估算大气扩散参数的新方法。这种新方法,仅需要从声雷达回波图上读出边界层结构的信息并取得常规地面测风资料,即可利用参数化公式进行计算,不需进行Pasquill稳定度分类。 所应用的参数化公式用外场观测资料进行了检验,表明公式计算结果与观测值比较符合。这种方法计算得到的扩散参数也与P-G扩散曲线进行了比较。     

重庆辐射雾的声雷达波与大气污染特征

结合气象观测和大气边界层探测资料，分析了１９９０年１月２日重庆雾的声雷达回波征，并与１９８９年１２月３０日雾的回波作了比较。结果表明，雾顶回波高度与逆温和相对湿度的转折高度一致；雾顶回波在雾的成熟期呈现波动，在消散期一下降过程。     

近山地区大气边界层声达探测的初步分析

应用单点声达在北京附近一个近山地区进行了低层大气温度结构的连续探测。分析了回波传真图象与地面风速的关系。发现在地形影响下逆温常呈层次结构。根据传真图讨论了对流混合层的发生与其上方逆温层演变过程的关系。并为在我国使用单点声达开展大气边界层的研究作了一些探索。     

多普勒声雷达对化音地区风场结构探测的初步分析

本文利用1990年8月多普勒声雷达在“HEIFE”区化音站探测的资料,对该地区的PBL结构进行了初步分析。结果表明,用声雷达回波强度的双对数廓线确定大气边界层高度仍不失为一有效的方法。大气边界层高度演变过程的特点是:白天对流层边界发展较快,但维持时间较短;而夜间稳定边界层维持时间较长,且在其发展较高时,在近地层又发展出一个新的稳定层结,呈现多层次的SBL结构。ML内垂直风速方差的归一化结果与Lenschow大致相同。另外,在一次冷锋过境天气背景下风场出现低空急流结构。     

新书架北大核心CSCD

《塔克拉玛干沙漠大气边界层和沙尘暴探测研究》王敏仲明虎等著该书系统介绍了塔克拉玛干沙漠大气边界层特征、沙漠腹地大气边界层风场变化、沙漠大气边界层高度与陆面参数的关系、沙漠对流边界层大涡模拟、沙漠极端深厚边界层过程对区域环流的反馈作用等内容,并首次利用边界层风廓线雷达、毫米波雷达开展了沙尘暴探测试验研究,计算归纳了沙尘暴的回波强度。     

雷达回波彩色图象显示和预报系统

大气物理研究所今年研制成功了一套建立在APPLE Ⅱ PLUS微型计算机基础上的雷达回波彩色图象显示和预报系统。它可以直接从雷达采集回波数据和其他必要的辅助数据,并把它们记录在磁盘或磁带上,以便随时重放。系统主要由微计算机、彩色图象显示器、打印机、磁盘(带)记录器和其他各种必要的输入、输出接口设备构成。目前,这个系统可以实现下列处理功能:(1)准实时高解析度彩色回波图象显示。在存贮器中,回波     

新型713C型天气雷达回波图象的合理显示方法

新型713C型天气雷达随机携带的工作软件,经过实际使用,发现存在一些问题,特别是其回波显示的失真程度较大、分辨率较低,影响了台风中心定位等工作.并且该软件不能在普通微机上显示回波图象,给资料传输带来困难.为此,我们在编制新的713C型天气雷达数据处理及图象显示软件包时,开发了一种合理的回波图象显示方法,以解决随机软件的不足.     

Observed and Modelled Convective Mixing-Layer Height at Dome C,Antarctica

The mixing-layer height is estimated using measurements from a high resolution surface-layer sodar run at the French-Italian station of Concordia at Dome C, Antarctica during the summer 2011–2012. The temporal and spatial resolution of the sodar allows the monitoring of the mixing-layer evolution during the whole diurnal cycle, i.e. a very shallow nocturnal boundary layer followed by a typical daytime growth. The behaviour of the summer mixing-layer height, variable between about 10- and 300 m, is analyzed as a function of the mean and turbulent structure of the boundary layer. Focusing on convective cases only, the retrieved values are compared with those calculated using a one-dimensional prognostic equation. The role of subsidence is examined and discussed. We show that the agreement between modelled and experimental values significantly increases if the subsidence is not kept fixed during the day. A simple diagnostic equation, which depends on the time-averaged integral of the near-surface turbulent heat flux, the background static stability and the buoyancy parameter, is proposed and evaluated. The diagnostic relation performance is comparable to that of the more sophisticated prognostic model.     

Summer boundary-layer height at the plateau site of Dome’C,antarctica

Measurements of the mean and turbulent structure of the planetary boundary layer using a sodar and a sonic anemometer, and radiative measurements using a radiometer, were carried out in the summer of 1999–2000 at the Antarctic plateau station of Dome C during a two-month period. At Dome C strong ground-based inversions dominate for most of the year. However, in spite of the low surface temperatures (between −50 and −20 °C), and the surface always covered by snow and ice, a regular daytime boundary-layer evolution, similar to that observed at mid-latitudes, was observed during summertime. The mixed-layer height generally reaches 200–300 m at 1300–1400 LST in high summer (late December, early January); late in the summer (end of January to February), as the solar elevation decreases, it reduces to 100–200 m. A comparison between the mixed-layer height estimated from sodar measurements and that calculated using a mixed-layer growth model shows a rather satisfactory agreement if we assign a value of 0.01–0.02 m s⁻¹ to the subsidence velocity at the top of the mixed layer, and a value of 0.003–0.004 K m⁻¹ to the potential temperature gradient above the mixed layer.     

Corrections for Wind-Speed Errors from Sodar and Lidar in Complex Terrain

The quality of lidar and sodar wind estimates is generally judged through comparisons with mast-mounted instruments, and the resulting regressions. Evaluation of the relative merits of lidars versus sodars is complicated by the fact that lidars are generally placed close to a mast whereas sodars are generally placed some distance from a mast so that acoustic reflections off the mast are reduced. This leads to the two technologies, lidar and sodar, not being compared in similar situations. Differences arising from the two geometries can be expected to be larger in complex terrain, where the wind regime can vary significantly spatially. The current work explores these differences in moderately complex terrain. Lidar–mast comparisons are performed with the lidar close to an 80 m mast, and sodar–mast comparisons performed with the sodar 300 m from the mast. Systematic variations in estimated wind speed are found to occur with height, consistent with predictions from a simple flow model. When the lidar was moved to the sodar location, further from the mast, there were significant changes in the estimated wind speeds and a reduction in correlation with the mast-based wind speeds, as expected. However, the correlation between collocated lidar and sodar winds was high. This finding emphasizes that any comparison of two remote sensing instruments needs to be through similar experiments, and that differences in accuracy often reported for the lidar and sodar technologies are likely to be contaminated due to poor comparison configurations. A method was devised to simulate the sodar being collocated with the mast, by using the lidar–sodar measurements and the lidar–mast measurements. It was found that there was then no statistically detectable difference between lidar–mast regressions and sodar–mast regressions for the particular lidar and sodar tested. Both remote sensing instruments were also found to be good estimators of Weibull parameters, as compared with those derived from mast data. The conclusion is that the sodar measured the winds above the sodar with a similar accuracy to the lidar measuring winds above the lidar.     

声雷达定量测量C_T~2中的几个问题

本文讨论了逾量衰减和风对声线的弯曲作用对声雷达接收功率的影响.分析和计算表明在很多情况下分子吸收、逾量衰减和风的影响对测量C_T~2是不能忽略的,不考虑这些因素有时可使C_T~2低估500％以上.引进有效湍流外尺度后使声散射截面表达式在实际应用中变得合理而简单.由简化的几何模型导出了风衰减因子,经计算和以往的实验事实相符.因此在原声雷达方程中应加入风衰减因子.声雷达方程加上逾量衰减算式、风衰减算式和分子衰减算式,组成了适合定量测量C_T~2的声雷达方程组.利用温度脉动仪测定低高度上的C_T~2值可使估算工作简化,此方法在多普勒声雷达上应用效果会较好,本文并给出了初步实验结果.     

An Independent Method to Determine the Height of the Mixed Layer

A method for the independent evaluation ofmixed-layer (ML) height, zi, has beenproposed. The ML height is determined bythe functional relationshipszi = 0.75 z/nv max or 0.53 z/nu max in which, z is a measuring height; nv max and nu max are normalized peak frequencies of lateral velocity component, v, and longitudinal velocity component, u, spectra at height z in the surface layer respectively. Using Doppler sodar data, the technique was shown to be feasible; it is easy to apply to micro-meteorological field experiments and works even for the ML top above the range of the sodar.     

Foehn signals detected by sodar wind and turbulence measurements in the Rhine Valley, Austria, during the MAP field phase

Summary Within the Mesoscale Alpine Programme MAP conducted in autumn 1999, the vertical structure and the temporal evolution of the planetary boundary layer (PBL) in the Rhine Valley 2km south of Lake Constance were observed with a Remtech PA2 sodar (sound-detection-and-ranging instrument) rendering half-hour averages of the three-dimensional wind profile within the lowest kilometre above ground. During Foehn events, tethered balloon soundings and wind profiler measurements were conducted in addition to the rawinsonde network which was built up for the MAP field campaign.The remote sensing instrument renders a surprisingly high number of valid data during south Foehn. Due to the frequent formation of a cold air pool with stable conditions below the Foehn flow with near-neutral static stability, even more sodar data is valid during Foehn periods than during no Foehn periods. A significant reduction of the sodar data quality is only observed during Foehn events with grounding of the Foehn at the sodar site due to high background noise. At higher levels, a Foehn signal can be detected from the sodar wind and turbulence intensitiy information. With Foehn, higher wind speeds and larger turbulence intensities occur than without Foehn. Comparisons to rawinsonde and tethersonde soundings and wind profiler measurements at sites nearby reveal the spatial inhomogeneity of the Foehn flow within this part of the valley as well as instrumental short-comings. Different methods to determine the mixing height using the vertical sounding devices lead to some uncertainty of mixing height estimates which however can reasonably be explained.     

Comparative analysis of sodar and ozone profile measurements in a complex structured boundary layer and implications for mixing height estimation

Profile data from simultaneous sodar and tethered balloon measurements have been analyzed with respect to the complex structure of the atmospheric boundary layer in the Upper Rhine Valley. Special attention was focused on ozone concentration profiles measured with a novel lightweight ozone sensor at the balloon. In general, good agreement was found between the signature of the ozone concentration profiles and special features of the backscattered sound intensity profiles. This allows reliable estimation of the mixing height from the sodar data even in a complex stable ABL, except for very shallow mixing layers (below about 75 m), which could not be detected by the sodar.     

Wavy Vertical Motions in the ABL Observed by Sodar

Some characteristics of wavelike motions in the atmospheric boundary layer observed by sodar are considered. In an experiment carried out in February 1993 in Milan, Italy, Doppler sodar measurements were accompanied by in situ measurements of temperature and wind velocity vertical profiles using a tethered balloon up to 600 m. The oscillations of elevated wavy layers containing intense thermal turbulence, usually associated with temperature-inversion zones, were studied by using correlation and spectral analysis methods. The statistics of the occurrence of wavelike and temperature-inversion events are presented. The height distributions of Brunt–Vaisala frequency and wind shear and their correlation within elevated inversion layers were determined, with a strong correlation observed between the drift rate of the wavy layers and the vertical velocity measured by Doppler sodar inside these layers. Spectral analysis showed similarities regarding their frequency characteristics. The phase speed and propagation direction of waves were estimated from the time delay of the signals at three antennae to provide estimates of wavelength. Moreover, wavelengths were estimated from the intrinsic frequency obtained from sodar measurements of the Doppler vertical velocity and oscillations of wavy turbulent layers. The two wavelength estimates are in good agreement.     

Acoustic sounder measurements of the planetary boundary layer at Maitri,Antarctica

The planetary boundary layer (PBL) over the Indian Antarctic station, Maitri (70.7° S; 11.7° E; 120 m asl) has been studied using a monostatic acoustic sounder. Acoustic sounder records reveal that the Antarctic PBL remains stably stratified throughout the year except for some periods in the peak summer months. The summertime PBL exhibits a diurnal variation with ground-based inversions developing at night and the convective plumes occurring during the peak sunlight hours. The cyclonic inflow of warm oceanic air towards the continent's interior from the coast helps in the development of the elevated layers and the Kelvin-Helmholtz waves observed on the sodar records.