共查询到20条相似文献，搜索用时 62 毫秒
1.
Presented is a review of the radiative properties of ice clouds from three perspectives: light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the singlescattering properties of individual ice crystals. The strengths and weaknesses associated with each approach are discussed.With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared(IR) bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed.The performance of ice cloud models based on the use of different ice habits to represent ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models(GCMs). The availability of the single-scattering properties of complex ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical ice particle models in GCM simulations for climate studies is proven. 相似文献
2.
The measurement of turbulent surface-layer fluxes by use of bichromatic scintillation 总被引：4，自引：2，他引：4
Scintillation measurements with a HeNe and a CO2 laser were used to derive turbulent fluxes of heat and momentum in the surface layer. This was achieved by the structure constant or dissipation technique, i.e., by relating the measured structure constants and inner scales of refractive index fluctuations to structure constants of temperature fluctuations and dissipation rates of turbulent kinetic energy, respectively, and then assuming Monin-Obukhov similarity.The resulting heat fluxes agree well with measurements using the eddy correlation technique but for averaging periods of 10 min, the optical data show a much smoother and physically more plausible behaviour. The optically derived friction velocities are in good agreement with estimates derived from wind velocity and surface roughness. It was also observed that for stationary conditions, 1-min averaged optical measurements already provide good estimates for longer averaged heat and momentum fluxes.Even though some uncertainty remains about the empirical constants and Monin-Obukhov similarity expressions used, the method clearly proves to be of great value for monitoring surface-layer turbulence. 相似文献
3.
北京城市热岛效应的流动观测和初步研究 总被引：4，自引：0，他引：4
采用车载气象观测仪器结合GPS定位、连续数据采集系统的流动观测方法研究了北京城区内不同城市地表覆盖物对城市局地小气候的影响和气象要素分布,发现城市下垫面分布与城市的温度和湿度有密切关系,一般在城市建筑物密集、水体和植被少的区域具有较高的气温和较低的相对湿度,在建筑物稀疏和植被、水体较多的区域则相反。观测结果表明,流动观测方法是对常规气象观测资料的有益补充,也是城市气候观测中的一种有效方法。 相似文献
4.
Stefan Emeis Klaus Sch?fer Christoph Münkel Roman Friedl Peter Suppan 《Boundary-Layer Meteorology》2012,143(1):25-35
Since 2006 different remote monitoring methods for determining mixing-layer height have been operated in parallel in Augsburg
(Germany). One method is based on the operation of eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter
intensities recorded with ceilometers provide information about the range-dependent aerosol concentration; gradient minima
within this profile mark the tops of mixed layers. Special software for these ceilometers provides routine retrievals of lower
atmospheric layering. A second method, based on sodar observations, detects the height of a turbulent layer characterized
by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component.
This information is extended by measurements with a radio-acoustic sounding system (RASS) that directly provides the vertical
temperature profile from the detection of acoustic signal propagation and thus temperature inversions that mark atmospheric
layers. Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from
2 years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde
for larger-scale humidity information. This evaluation is designed to ensure mixing-layer height monitoring from ceilometer
data more reliable. 相似文献
5.
利用多角度POLDER偏振资料实现陆地上空大气气溶胶光学厚度和地表反照率的同时反演 II. 实例分析 总被引：1，自引：0，他引：1
由于陆地地表反照率的复杂性,陆地上空气溶胶的反演一直是卫星对地观测的一个难点,针对这个难点,作者提出联合利用偏振反射率和总反射率提取陆地上空大气气溶胶光学厚度和地表反照率及其区域分布的反演方案,提出了利用NCEP资料订正由海拔高度引起的Rayleigh散射变化的具体方法,并利用POLDER（POLarization and Directionality of Earth's Reflectance）的LEVEL-1B资料进行实际反演计算,给出中国华北地区气溶胶光学厚度和地表反照率的区域分布。反演结果与地基观测进行了对比验证分析,结果表明,综合利用标量辐射和偏振信息的可以实现区域乃至全球尺度的大气气溶胶和地表反照率的定量反演。 相似文献
6.
A differential optical absorption spectroscopy (DOAS)-like algorithm is developed to retrieve the column-averaged dry-air mole fraction of carbon dioxide from ground-based hyper-spectral measurements of the direct solar beam. Different to the spectral fitting method, which minimizes the difference between the observed and simulated spectra, the ratios of multiple channel-pairs——one weak and one strong absorption channel——are used to retrieve X CO2 from measurements of the shortwave infrared (SWIR) band. Based on sensitivity tests, a super channel-pair is carefully selected to reduce the effects of solar lines, water vapor, air temperature, pressure, instrument noise, and frequency shift on retrieval errors. The new algorithm reduces computational cost and the retrievals are less sensitive to temperature and H2O uncertainty than the spectral fitting method. Multi-day Total Carbon Column Observing Network (TCCON) measurements under clear-sky conditions at two sites (Tsukuba and Bremen) are used to derive X CO2 for the algorithm evaluation and validation. The DOAS-like results agree very well with those of the TCCON algorithm after correction of an airmass-dependent bias. 相似文献
7.
On the basis of forward IR radiation transfer analyses for an atmosphere containing semi-transparent, non-black cirrus, parameterization equations are derived for the retrieval of the cloud optical depth and cloud temperature utilizing AVHRR 3.7 and 10.8 μum channels. The retrieval techniques developed involve the use of either dual-frequency or dual-scanning angle radiance observations. We show that the cloud optical depth and cloud temperature may be inferred successively from the observed brightness temperature differences using these two techniques. Numerical experiments anderror analyses demonstrate that the dual-frequency method is specifically appropriate for optically thin cirrus cases (τ <1). In case the optical depth of cirrus is close to 3, combination of dual-frequency and dual-scanning angle methods is shown to give reasonable accuracy for the cloud optical depth and temperature retrieval. 相似文献
8.
Light extinction by atmospheric particles is strongly dependent on their chemical composition and water content. Since light extinction directly impacts climate, optical measurements of atmospherically relevant aerosols at varying relative humidities (RH) are needed. Recent studies have highlighted the possibility that some atmospheric aerosols are glassy under ambient conditions. Here, the particle optical growth factor, fRHext, was measured for liquid and glassy particles using cavity ring-down aerosol extinction spectroscopy. The particles were composed of ammonium sulfate (AS), 1,2,6-hexanetriol, sucrose, raffinose, and mixed particles containing AS and either sucrose or raffinose. Both sucrose and raffinose can be glassy at room temperature. For the pure organics, the highly viscous sucrose and raffinose particles have similar optical growth curves to the liquid 1,2,6 hexanetriol particles. However, for particles composed of sucrose or raffinose mixed with AS, optical growth depends on the AS weight-percent, which in turn controls the phase state of the AS and ultimately the water uptake. 相似文献
9.
陆地上空标量辐射对地表反射率和大气气溶胶散射都具有很强的敏感性,而偏振反射只对大气气溶胶敏感,对地表不敏感。根据这个原理并结合POLDER(POLarization and Directionality of Earth Reflectance)资料的特点,作者提出综合利用标量辐射和偏振反射信息来实现陆地上空大气气溶胶和地表反照率的同时反演。首先,利用多角度偏振辐射观测提取大气气溶胶光学参数,再利用标量辐射测量对偏振反演结果作进一步筛选和订正,同时获得地表反射率。数值模拟试验结果证明,仅利用偏振信息只能获取大气气溶胶信息,而且其结果误差较大,特别是对于散射作用较强的短波长通道如670 nm误差更大,但经过标量辐射订正后的结果得到明显改善,气溶胶光学厚度和地表反射率与真实值之间相关系数都达到0.99以上。为提高查找表的计算效率,提出并建立了反演方案所需要的半参数化数值表,利用内插方法寻求气溶胶光学厚度和地表反射率的数值解的反演方法。 相似文献
10.
We examine the efficacy of two methods commonly used to estimate the vertical turbulent fluxes of momentum and sensible heat
from routinely observed mean quantities in the surface layer under stable stratification. The single-level method uses mean
wind speed and temperature measurements at a single height, whereas the two-level method uses mean wind speed measurements
at a single height and mean temperature measurements at two heights. These methods are used in popular meteorological processors
such as the U.S. Environmental Protection Agency approved AERMET and CALMET to generate inputs for dispersion simulations.
We use data from a flux station of the U.K. Met Office at Cardington for comparison. It is found that the single-level method
does not describe the flux variation in the weakly stable regime at all, because of its assumption that the temperature scale,
i.e. the ratio of the kinematic sensible heat flux to the friction velocity, is constant, which is plausible only under strongly
stable conditions. On the other hand, the two-level method provides a physically realistic variation of the fluxes with stability,
but the required temperature measurements at two levels are usually not available on a routine basis. If measurements of the
standard deviation of temperature are also available, in addition to the mean temperature at a single level, then they can
be usefully employed in a third (single-level) method, with the consequence that the computed fluxes are very similar to those
obtained from the two-level method. An improvement to the original single-level method is considered, and flux calculations
under low wind conditions are also discussed. 相似文献
11.
T. Vrhovec 《Meteorology and Atmospheric Physics》1990,43(1-4):235-240
Summary An objective procedure of a three-dimensional temperature analysis in a topography following (zeta) coordinate system is presented. Temperature data from various conventional sources (ground stations, RAWIN, synoptic analysis) are interpolated into the grid points of the zeta system (the horizontal grid distance is 1 km, vertical resolution is 11 levels up to 2500 m) by a topography variability considering horizontal interpolation. As the correlations between the synop and also the upper air data from pairs of stations on different sides of a mountain barrier show a rapid decrease (Lanzinger and Steinacker, 1989), the Euclidic distances between the points with measurements and the grid points are corrected according to the variability of the gird points are corrected according to the variability of the topography between the two points. If the topography between the two points is flat, or if there is only a valley, the Euclidean distance is used as an interpolation distance. In case of a ridge between the two poinst the interpolation distance is increased according to the topography height variation and the stability of the air mass. In the vertical interpolations a synthetic temperature profile is used made of the data from Rawin, the measurements from meteorological tower and the measurements from some meteorological stations located at high altitude.The grid point temperature values are adjusted to satisfy quasi-stationarity condition, considering advective and diabatic changes of the temperature. A variational formalism in a weighted least square sense in the zeta coordinate system is developed and the boundary conditions are specified. The results (3-D temperature fields and the fields of local derivative of temperature) for a large pre-alpine basin (the Ljubljana basin in the central part of Slovenia, Yugoslavia, 50×50 km) are presented and the usefullness of the adjustement procedure is discussed.With 5 Figures 相似文献
12.
Summary Acoustic travel time tomography is demonstrated as a technique for remote monitoring of near surface air temperature and
wind fields.
An experimental procedure is presented which provides line-averaged values of the effective sound speed changing with air
temperature and wind vector. In this study the travel times of sound signals at defined propagation paths between different
acoustic sources and receivers were measured. The travel time data were inverted into effective sound speed values by using
a special tomographic algorithm (Simultaneous Iterative Reconstruction Technique) to obtain area-averaged meteorological quantities
(air temperature, wind speed).
The method of acoustic travel time tomography will be applied to the atmosphere in order to directly provide spatially averaged
data which are needed for evaluation of large-eddy simulation and microscale meteorological models as well as to complete
conventional point measurements.
Received November 4, 1998 Revised April 7, 1999 相似文献
13.
A simple linear regression method is developed to retrieve daily averaged soil water content from diurnal variations of soil temperature measured at three or more depths. The method is applied to Oklahoma Mesonet soil temperature data collected at the depths of 5, 10, and 30 cm during 11-20 June 1995. The retrieved bulk soil water contents are compared with direct measurements for one pair of nearly collocated Mesonet and ARM stations and also compared with the retrievals of a previous method at 14 enhanced Oklahoma Mesonet stations. The results show that the current method gives more persistent retrievals than the previous method. The method is also applied to Oklahoma Mesonet soil temperature data collected at the depths of 5, 25, 60, and 75 cm from the Norman site during 20-30 July 1998 and 1-31 July 2000. The retrieved soil water contents are verified by collocated soil water content measurements with rms differences smaller than the soil water observation error (0.05m~3 m~(-3)). The retrievals are 相似文献
14.
Inertial dissipation methods are based on measurements of the structure parameters of momentum, temperature and humidity. The most serious problems arise when experimental errors and uncertainties in the meteorological constants produce uncertainties in the calculated fluxes.In order to design an experimental layout to use an optical technique to measure fluxes, we need to perform an accurate error analysis. A Monte Carlo analysis is presented here to simulate the results and to analyze the propagation of statistical errors affecting the measurements. Results show that the coupling of inertial dissipation methods with optical methods is promising and a field experiment, based on the joint techniques, is feasible.This work was partially supported by M.P.I. (60%) grants of the Italian Ministry of Education. 相似文献
15.
16.
K. Blümel 《Boundary-Layer Meteorology》2001,98(2):183-218
By means of the algorithm presented in Part I of this study, the temporal course H(t) and the daily mean H of the sensible heat flux H can be determined from measurements of the thermodynamic surface temperature (as a function of time) and from a one-time-of-day air temperature observation. Inaddition to these temperatures, one needs estimates of daily mean wind speed,of the roughness lengths of momentum and heat transfer, and of the displacementheight. In Part I, the algorithm was derived for areas with homogeneous surfaces,i.e., with uniform surface temperature, and the method was verified with measurements taken during several field campaigns. The root mean square error for the temperature difference between surface and air, in the comparison between measurement and model, amounted to one or two kelvin, and the error of H was 10 to 25 per cent. The method can be used to determine the sensible heat flux from measurements of surface temperatures by satellites, but can also be applied to ground based measurements.In Part II, the procedure is generalized for areas that consist of various surface types (sub-regions) with different surface temperatures, and can be usedwhen only a few (at least one) air temperature measurements per day are available over only one of the different sub-regions. This generalization should allow improvements to the estimates for H(t) by means of temperature measurements from, e.g., NOAA/AVHRR or LANDSAT/TM, taking into account the heterogeneity of the area contained in one METEOSAT pixel. Criteria are given as to whether effective (areal mean) surface temperatures and roughness lengths may be used for the computation of H or if the above mentioned generalized procedure has to be applied. The new algorithm is verified by measurements sampled during the field campaigns EFEDA 91 (Spain) and HIBE 89 (Hildesheimer Börde in Germany), and by using synthetic data (due to the lack of measured data) for one further combined surfacetype [soil and water (lakes)]. 相似文献
17.
Aloysius K. Lo 《Boundary-Layer Meteorology》1979,17(4):465-484
This paper proposes a numerical technique based on the least-square error method for evaluating fluxes and other surface-layer parameters. The special feature of this method is that it requires no a-priori knowledge of either the temperature profile or the roughness length z
0. The accuracy of the method has been tested on both the Kansas and the Wangara experimental data. Results obtained compared favourably with those from direct measurements as well as from other studies using conventional approaches. 相似文献
18.
An investigation of flux-variance methods and universal functions applied to three land-use types in unstable conditions 总被引：3，自引：0，他引：3
Jacob Padro 《Boundary-Layer Meteorology》1993,66(4):413-425
Fluxes calculated from three flux-variance methods, which depend upon three different forms of the normalized standard deviation functions (referred to as universal functions) of the surface atmospheric stability have been tested and compared with measurements for temperature and water vapour. The flux measurements were made over a fully leafed deciduous forest, a leafless deciduous forest and over a wetland region during the summer. The first method (referred to as the variance method) allows for certain constants, which are associated with the universal functions, to vary with land-use type and the scalar for which the flux is computed; the second method uses the form of the universal function developed by Tillman, which depends upon two constants; and the third method, known as the Wyngaard method, is the simplest and depends upon one constant only. Flux estimates from the variance method yield the best agreement with observations over the three hand-use types and the Wyngaard method appears to yield estimates that are quite comparable. The measurements for the univeral functions agree better with the Wyngaard function for temperature and better with the Tillman function for water vapour, although both show some scatter. The simplest formula developed by Wyngaard may be considered adequate for computing fluxes of temperature and water vapour from their variances. The main advantage of the formulae is to help define an upper limit for actual fluxes. 相似文献
19.
CE318太阳光度计观测资料应用前景及其解读 总被引：8，自引：0，他引：8
2002年中国气象局在沙尘暴各观测站点安装了CE318太阳光度计,用于探测大气气溶胶。为了使研究人员了解CE318太阳光度计工作原理、数据存储格式及解读方法,使这批观测数据很好地发挥作用,该文介绍了气溶胶气候效应的研究现状,分析了应用太阳光度计这种地基手段探测气溶胶的优势以及探测数据的应用前景。同时,针对光度计原始观测资料直接应用的瓶颈问题———资料解读方案进行了讨论,包括定标、气溶胶光学厚度的计算、光度计数据质量控制方法等。结合新疆塔中站光度计观测资料,列举了采用Langley法进行定标和计算气溶胶光学厚度的步骤。 相似文献
20.
利用台站资料定标太阳光度计效果评估 总被引：4，自引：1，他引：3
运用Langley方法、采用法国CE318太阳光度计在台站的观测记录为光度计定标,提出一种较客观的数据处理方法,主要分为4步：①利用Langley法对全年资料进行预处理,得到各通道定标常数、Langley法线性拟合相关系数、550nm的气溶胶光学厚度等;②以线性拟合相关系数的阈值大小（如440nm相关系数大于等于0．99）、定标期间550nm的平均气溶胶光学厚度小于等于0．15、半天（上午或下午）参与拟合的数据个数大于等于8组为条件,对预处理数据进行筛选;③根据光度计电压信号图像、最大值再次选取定标常数;④对最终选出的多组定标常数取平均值。对2002、2005年,乌鲁木齐、塔中、哈密、和田4个站点光度计资料进行试验,定标系数与出厂定标值（2002年）、北京定标值（2005年）比较后,4个站点的定标误差基本控制在8．5％以内（和田除外）,说明这种定标步骤有一定的参考价值。 相似文献