共查询到20条相似文献，搜索用时 166 毫秒
1.
大气折射率结构常数描述了大气湍流起伏的强弱,它表征了大气折射率随机不均匀性的剧烈程度。光波和无线电波在大气中传播时会受到大气湍流的影响而产生各种不良效应,如:光斑漂移、闪烁、相位起伏等。因此,对大气折射率结构常数的研究具有重要的意义。本文利用常规探空资料对微波波段大气折射率结构常数进行了仿真研究,结果表明:在低空,特别是大气边界层之内,大气折射率结构常数主要为湿度所贡献;在高空,大气折射率结构常数主要为温度所贡献。在微波波段,影响大气折射率结构常数最大的气象因子并不是温湿压的大小,而是它们梯度的大小,其中湿度梯度的大小对其影响最大,在实际的低空测量大气折射率结构常数时,主要考虑湿度梯度与温度梯度的影响。 相似文献
2.
风廓线雷达对塔克拉玛干沙漠晴天边界层的探测分析 总被引：2，自引：0，他引：2
利用塔克拉玛干沙漠大气环境观测试验站2010年8和10月边界层风廓线雷达资料,分析了沙漠晴天边界层湍流、大气温度、水平风速风向以及垂直速度的发展演变特征和日变化规律。研究表明：（1）大气折射率结构常数（C_n~2）能较好地反映晴空湍流对电磁波的后向散射能力,可以详细刻画湍流发展旺盛区域的高度、强度及其演变特征;沙漠夏季白天湍流发展剧烈,旺盛区域顶部可达4000 m高度左右。（2）RASS系统对沙漠边界层大气温度的探测具有较好的可信度,其近地边界层温度符合一般的日变化规律,昼夜温差显著,白天高温维持时间长,升温过程相对滞后于近地表气温。（3）风廓线雷达对大气风场的探测结果与地面风速风向一致,沙漠晴天主要受东风和东北风控制,风速较小,平均在2.0～6.0 m·s~（-1）范围变化。（4）沙漠腹地大气垂直速度变化符合静力平衡理论,铅直方向运动很弱,一般在-1.0～1.0 m·s~（-1）范围波动。 相似文献
3.
大气湍流引起的折射率起伏会导致光信号的振幅和相位发生随机波动,同时日益严重的城市雾霾现象带来的系统性能降低问题也不可忽视.基于湍流相位波动和激光器相位噪声的缓慢时变特性,本文提出了将DAML相位估计算法应用到空间相干光通信系统中来提高系统性能,并推导了在大气湍流、激光器相位噪声以及各种天气状况衰减效应影响下,针对DQPSK信号的DAML相位估计系统的误码率,最后重点分析了在雾、霾天气条件下该系统的传输距离限制和波长选择特性.仿真结果表明：湍流相位波动造成的信噪比损失低于0.1 dB;在雾和霾天气下,相较于传统的OOK IM／DD FSO通信系统,DAML相位估计系统在不同的大气湍流环境中至少有500 m的传输距离优势;在霾和薄雾天气,传输波长为1 550 nm的DAML系统比波长为850 nm的系统的性能更优,但在能见度低于200 m的浓雾天气,系统性能基本与波长选择无关. 相似文献
4.
切变湍流的相干结构是湍流研究中的重大发现,它表明湍流在表面上看来不规则运动中具有可检测的有序运动,这种相干结构在切变湍流的脉动生成和发展中起着主宰作用.因此识别和提取相干结构对于认识和研究湍流是非常重要的.用数字滤波法将包含相干结构的大尺度信号提取出来以后,再用子波分析,根据子波能量极大值的判别方法,分别确定出大气湍流三个方向上的速度脉动信号相干结构的频率或时间尺度,然后由确定尺度上的连续子波反演公式,提取出大气湍流三个方向上的速度脉动信号相干结构所对应的波形. 相似文献
5.
The propagation of optical and electromagnetic waves is affected by small-scale atmospheric turbulence, quantified by the
structure parameter of the refractive index. In the atmospheric surface layer, the mean structure parameter Cn2{C_{n}^{2}} , as averaged over the large-scale turbulence, relates to meteorological forcings through well-documented relationships.
Present-day numerical weather forecast models routinely produce these forcings at the global scale. This study introduces
a method where the products of such a model are used to calculate the mean optical turbulence near the surface. The method
is evaluated against scintillometry measurements over climatologically distinct sites in Western Europe. The diurnal cycle
modulation, and regional and seasonal contrasts, are all reproduced by our predictions. Hence, the present method explains
and predicts some essential aspects of the meteorological variability of Cn2{C_{n}^{2}} near the surface. The noted discrepancies combine instrumental limitations, site peculiarities, differences related to distinct
averaging procedures, and model errors, notably from weather forecasts. The minute-scale fluctuations of the measured scintillation
rate are also analysed in the light of the forecast weather conditions. Fair-weather daytime periods consistently show a small
short-term variability compared to the nighttime and perturbed weather periods. Thus, this short-term variability appears
to have a predictable component. 相似文献
6.
在现有GPS星座和大气球对称假设条件下，利用射线追踪法对掩星事件进行了数值模拟，讨论了大气折射指数垂直分布、LEO卫星轨道倾角和高度对GPS掩星切点水平漂移的影响情况。结果表明:在太阳活动剧烈的白天和夜间两种典型情况下，切点平均水平漂移变化约20 km；对735 km高度的LEO卫星来说，轨道倾角在130°附近时，切点平均水平漂移最小，并随着倾角向0°或180°变化，切点平均水平漂移均增大，但在55°附近时随倾角变化稍有波动；对倾角为70°的LEO卫星来说，当轨道高度从400 km变化到1500 km时，切点平均水平漂移变化约141 km，且随高度增加而单调减小 相似文献
7.
利用东疆红柳河黑戈壁下垫面陆气相互作用观测站2017年近地大气边界层梯度探测资料和红柳河气象站天气现象观测数据,分析该地区典型晴天条件下的近地层风速、温度和比湿的四季廓线特征。结果表明:四季近地层风廓线变化规律明显。典型晴天条件下,在0.5～4 m高度内风速随高度的增加而变大的速度较快,在4～32 m范围内,白天风速随高度增大较缓慢,但夜间出现快速增大;存在明显的夜间逆温,逆温层主要集中在4～32 m,冬季逆温强于夏季,晨间0.5～32 m间的温度差可达4.6℃,且红柳河四季的气温日较差均较大,秋季可达到15.7℃;夜间比湿高于白天,秋、冬季夜间逆湿层出现在10～32 m,其比湿差为0.15 g/kg左右,夏季无逆湿现象。 相似文献
8.
The presence of coherent structures in turbulent shear flows suggests order in apparently random flows. These coherent structures play an important dynamical role in momentum and scalar transport. To develop dynamical models describing the evolution of such motion, it is necessary to detect and isolate the coherent structures from the background fluctuations. In this paper, we decomposed atmospheric turbulence time series into large-scale eddies, which include coherent structures and small eddies, which are stochastic by using Fourier digital filtering. The wavelet energy computed for the three components of the velocity fluctuations in the large-scale eddies appears to have local maximum values at certain time scales, which correspond to the scales or frequencies of coherent structures. We extract coherent signals from large-scale vortices at this scale by inverse wavelet transform formulae. This method provides an objective technique for examining the turbulence signal associated with coherent structures in the atmospheric boundary layer. The average duration of coherent structures in three directions based on Mexican hat wavelets are 33 s, 34 s and 25 s respectively. Symmetric andanti-symmetric wavelet basis functions give almost the same results. The main features of the structures during the day and night have little difference. The dimensionless durations for u, v and w have linear correlations with each other. These relationships are insensitive to the wavelet basis. 相似文献
9.
Christen Andreas Meier Fred Scherer Dieter 《Theoretical and Applied Climatology》2012,108(1-2):301-324
This study presents an attempt to resolve fluctuations in surface temperatures at scales of a few seconds to several minutes using time-sequential thermography (TST) from a ground-based platform. A scheme is presented to decompose a TST dataset into fluctuating, high-frequency, and long-term mean parts. To demonstrate the scheme’s application, a set of four TST runs (day/night, leaves-on/leaves-off) recorded from a 125-m-high platform above a complex urban environment in Berlin, Germany is used. Fluctuations in surface temperatures of different urban facets are measured and related to surface properties (material and form) and possible error sources. A number of relationships were found: (1) Surfaces with surface temperatures that were significantly different from air temperature experienced the highest fluctuations. (2) With increasing surface temperature above (below) air temperature, surface temperature fluctuations experienced a stronger negative (positive) skewness. (3) Surface materials with lower thermal admittance (lawns, leaves) showed higher fluctuations than surfaces with high thermal admittance (walls, roads). (4) Surface temperatures of emerged leaves fluctuate more compared to trees in a leaves-off situation. (5) In many cases, observed fluctuations were coherent across several neighboring pixels. The evidence from (1) to (5) suggests that atmospheric turbulence is a significant contributor to fluctuations. The study underlines the potential of using high-frequency thermal remote sensing in energy balance and turbulence studies at complex land–atmosphere interfaces.
相似文献10.
基于湍流散射理论,运用边界层风廓线雷达 (WPR) 联合RASS (Radio Acoustic Sounding System), GPS/PWV (Global Position System/Precipitable Water Vapor) 进行全遥感系统的大气比湿廓线反演试验,并对影响因子进行分析。利用2011年8—9月云南大理综合探测试验数据的反演结果与探空数据进行比较分析,结果表明:WPR联合探空的温度廓线和起始边界比湿 (q0) 反演大气比湿廓线,与探空大气比湿廓线相比具有相同的变化趋势,标准差为0.84 g·kg-1,误差随高度增加呈递增趋势;WPR联合RASS, GPS/PWV数据反演大气比湿廓线,与探空大气比湿廓线的标准差为0.85 g·kg-1。参加反演的数据中,折射指数结构常数Cn2与谱宽σturb2对反演影响最大,反演算法中大气折射指数梯度M符号的判断对反演精度也有较大影响。 相似文献
11.
2019年3月,利用相干多普勒测风激光雷达首次在辽东湾西部绥中地区进行了风廓线测量试验。根据研究区域海岸线走向采用风向的十六分位法定义局地海风和陆风,分析和提取海陆风特征验证了多普勒测风激光雷达在春季季风间断期间观测海陆风的可行性,并计算和分析了大气边界层湍流能量的变化以及回流水平变化等特性。结果表明：1）绥中地区春季存在明显的海陆风环流特征,测风激光雷达观测海陆风出现的时间与地面自动气象站观测的数据较为一致,符合海陆风日的定义。2）海陆风日发生时,水平局地回流指数（RF）较小,1.2 km以下的RF值小于0.5,使得污染物循环累积,较易形成雾霾天气;但是海风时大气边界层的高度可达1 km以上,有利于低层大气污染物向高层扩散,减轻低层大气污染。研究结果为该地边界层参数化方案的设计和污染的防治提供了参考依据。 相似文献
12.
An observational analysis of the structures and characteristics of a windy atmospheric boundary layer during a cold air outbreak in the South China Sea region is reported in this paper. It is found that the main structures and characteristics are the same as during strong wind episodes with cold air outbreaks on land. The high frequency turbulent fluctuations(period<1 min) are nearly random and isotropic with weak coherency, but the gusty wind disturbances(1 min相似文献
13.
In the present study, three wavelet basis functions (Mexican-hat, Morlet, and Wave) were used to analyze atmospheric turbulence data obtained from an eddy covariance system in order to determine effect of six meteorological elements (three-dimensional wind speed, temperature, and CO2 and H2O concentrations) on the time scale of coherent structures. First, we used the degree of correlation between original and reconstructed waveforms to test the three wavelets’ performance when determining the time scale of coherent structures. The Wave wavelet’s reconstructed coherent structure signal best matched the original signal; thus, it was used for further analysis of the time scale, number, and time cover of the meteorological elements. We found similar results for all elements, though there was some internal variation, suggesting that coherent structures are not inherently dependent on these elements. Our results provide a basis for proper coherent structure detection in atmospheric turbulence and improve the understanding of similarities and differences between coherent structure characteristics of different meteorological elements, which is helpful for further research into atmospheric turbulence and boundary layers. 相似文献
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利用济南站边界层风廓线雷达（简称WPR）观测资料,对大气折射率结构常数（简称Cn2）确定对流边界层高度（简称CBLH）的技术难点进行了研究,通过对实测Cn2数据廓线进行求导变换突出其变量特征,提出了一种确定CBLH的方法,即e指数拟合曲线的偏离度法。结果表明：经案例分析和与实测对比,证实其判断的结果与L探空实测虚位温梯度法、湿度梯度法等的判断结果总体一致,平均值分别与后两者结果相差+10.4 m、-21.8 m,最小值差-70 m、-120 m,最大值差+50 m、+80 m,与后两者的相关系数分别达0.988、0.980。不同方法对比表明,31组样本中有7组的极大值法判断结果与偏离度法、虚位温梯度法存在较大差异,在CBLH判别时偏离度法总体优于极大值法。偏离度法能够将夏季CBLH确定结果的绝对误差降至近似WPR垂直分辨率水平。 相似文献
16.
In order to provide wind profiles for the microscale numerical simulation of wind farm with complex terrain,using the 100 m tower atmospheric turbulence observation experiment data in 2010 in Hebei Province offered by National Climate Center, the variation characteristics of wind profile under the different atmospheric stability conditions are analyzed, and the wind profile expression based on the local similarity theory is established. The results show that:(1) In spring, the occurrence probability of unstable stratification in the Hebei coastal area is as high as 28%, and the probability of stable stratification is more than 43% while, in summer, the probability of occurrence of unstable stratification is as high as 80% with a lower probability for stable stratification; and(2) for stable stratification, the characteristics of atmosphere change is dramatic in terms of the vertical direction, which need to be treated layer by layer.According to the atmospheric turbulence observation experiment data above, under stable stratification, the relationship between the dimensionless velocity gradient and the stability ζ can be expressed as 1 +βmζ, with βm changing with the height: βm takes 4.1-4.3 under 30 m, βm takes 4.6-4.7 between 30-50 m, and βm takes 6.3-6.7 over 50 m. 相似文献
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This paper uses a Modified Soil-Plant-Atmosphere Scheme (MSPAS) to study the interaction betweenland surface and atmospheric boundary layer processes. The scheme is composed of two main parts:atmospheric boundary layer processes and land surface processes. Compared with SiB and BATS, which arefamous for their detailed parameterizations of physical variables, this simplified model is more convenientand saves much more computation time. Though simple, the feasibility of the model is well proved inthis paper. The numerical simulation results from MSPAS show good agreement with reality. The schemeis used to obtain reasonable simulations for diurnal variations of heat balance, potential temperature ofboundary layer, and wind field, and spatial distributions of temperature, specific humidity, vertical velocity,turbulence kinetic energy, and turbulence exchange coefficient over desert and oasis. In addition, MSPAS isused to simulate the interaction between desert and oasis at night, and again it obtains reasonable results.This indicates that MSPAS can be used to study the interaction between land surface processes and theatmospheric boundary layer over various underlying surfaces and can be extended for regional climate andnumerical weather prediction study. 相似文献
19.
有关大气湍流的几个问题 总被引：3，自引：0，他引：3
浑沌(chaos)概念的提出,有关大气湍流的若干问题有深入讨论的必要。根据我们近几年研究对如下问题提出自己见解,供深入讨论:确定的动力系统可以描述大气湍流,大气湍流可以用有限维动力系统来研究,速度切变?u/?z有两重性,稳定层结下可以出现湍流,Lorenz方程的意义及局限性,湍流发生 相似文献
20.
用最大熵谱分析法对南京、上海两地局地大气折射指数气候变化特征进行诊断，探讨了自回归模式的阶数不同对谱的影响，并从不同样本数的熵谱中提取出稳定的周期和谱峰值，所得结果可以作为预报大气折射指数变化的气候背景。 相似文献