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1.
Tower platforms, with instrumentation at six levels above the surface to a height of 30 m, were used to record various atmospheric
parameters in the surface layer. Sensors for measuring both mean and fluctuating quantities were used, with the majority of
them indigenously built. Soil temperature sensors up to a depth of 30 cm from the surface were among the variables connected
to the mean data logger. A PC-based data acquisition system built at the Centre for Atmospheric Sciences, IISc, was used to
acquire the data from fast response sensors. This paper reports the various components of a typical MONTBLEX tower observatory
and describes the actual experiments carried out in the surface layer at four sites over the monsoon trough region as a part
of the MONTBLEX programme. It also describes and discusses several checks made on randomly selected tower data sets acquired
during the experiment. Checks made include visual inspection of time traces from various sensors, comparative plots of sensors
measuring the same variable, wind and temperature profile plots, calculation of roughness lengths, statistical and stability
parameters, diurnal variation of stability parameters, and plots of probability density and energy spectrum for the different
sensors. Results from these checks are found to be very encouraging and reveal the potential for further detailed analysis
to understand more about surface layer characteristics. 相似文献
2.
Wind tunnel experiments on the turbulent transmission over the near surface layer of different surfaces 总被引：1，自引：0，他引：1
To understand the generation and development mechanism of soil erosion, data of the wind profile from wind tunnel experiments were used, and the characteristics of the turbulent transmission with free stream velocity and the properties of the surfaces in arid and semi-arid regions were studied by the atmospheric aerodynamic method. The result showed that the turbulent momentum fluxes are proportional to the velocity and the roughness of the surfaces. In addition, they are closely related to the density of the roughness elements; the turbulent exchange coefficient over the near surface layer increases with height. 相似文献
3.
In the estimation of momentum fluxes over land surfaces by the bulk aerodynamic method, no unique value of the drag coefficient
(C
D) is found in the literature. The drag coefficient is generally estimated from special observations at different parts of
the world. In this study an attempt is made to estimate drag coefficient over the western desert sector of India using data
sets of Monsoon Trough Boundary Layer Experiment (MONTBLEX) during the summer monsoon season of 1990. For this purpose, the
fast and slow response data sets obtained simultaneously from a 30 m high micro-meteorological tower at Jodhpur are used.
All the observations used in this study are confined to a wind speed regime of 2.5–9.0 ms−1.
A comparison of momentum fluxes computed by eddy correlation (direct estimation) with profile and bulk aerodynamic (C
D = 3.9 × 10−3, Garratt, 1977) methods revealed that though the nature of variation of the fluxes by all these methods is almost similar,
both the indirect methods give an under-estimated value of the fluxes. The drag coefficient is estimated as a function of
wind speed and surface stability by a multiple regression approach. An average value of the estimated drag coefficient is
found to be of the order of 5.43 × 10−3. The estimated value ofC
D is validated with a set of independent observations and found to be quite satisfactory. The recomputed momentum fluxes by
bulk aerodynamic method using the estimated drag coefficient are in close agreement with the directly estimated fluxes. 相似文献
4.
基于2005—2016年青藏高原多年冻土区唐古拉和西大滩站的气象、涡动通量以及活动层资料,利用涡动相关法、气象梯度法和SHAW模型等方法探究了气候变化背景下高原多年冻土区地表能量通量变化规律及其对活动层的影响。结果表明：2005—2016年唐古拉和西大滩气温、地气温差有所升高,年降水量、10 cm土壤含水量及风速有所下降。2005年以来唐古拉和西大滩净辐射（Rn ）与感热（H）呈增加趋势,潜热（LE）呈减小趋势,地表土壤热通量（G）变化较小。唐古拉和西大滩地表能量通量季节变化明显,但受海拔、纬度、坡向、土壤冻融过程、降水、下垫面状况等因素的影响,地表能量通量存在区域差异。研究时段内,唐古拉和西大滩地表冻结指数与土壤热通量呈负相关;融化指数、活动层厚度与土壤热通量呈正相关,融化期间土壤热通量积累量与融化深度的变化呈线性增加关系。 相似文献
5.
Numerical simulation of sea breeze characteristics observed at tropical coastal site,Kalpakkam 总被引：1，自引：0，他引：1
Sea breeze characteristics around Kalpakkam tropical coastal site are studied using an Advanced Regional Prediction System
(ARPS) mesoscale model, which is non-hydrostatic, compressible atmospheric prediction model following the terrain coordinate
system. Various options such as surface physics, atmospheric radiation physics, Coriolis force, microphysics, cumulus parameterization
and 1.5 level TKE closure scheme for diffusion are included in the model.
A joint meteorological field experiment was carried out by IITM-Pune and IGCAR at Kalpakkam by deploying state-of-the-art
sensors and tether balloon systems for observing the height profiles of meteorological parameters. The data obtained from
the field experiment are used here to compare the results from numerical simulations. From the simulated results, it is seen
that duration of the sea breeze is 6 hours which agrees well with the observations. The height of the Thermal Internal Boundary
Layer (TIBL) is also simulated from the vertical profiles of potential temperature. Simulated wind speed and wind directions
are compared with the 50 m tower data and potential temperature profiles are compared with the kytoon data. Results are in
good agreement with the observed values except during night time wherein a small difference is seen in the wind speed. 相似文献
6.
Two models have been developed by applying conditions of continuity between the roughness sublayer and the top of vegetation
canopy having constant foliage distribution. Massman's cosh-type of wind profile and Albini's exponential wind profile have
been used to derive expressions for shear stress, displacement height and roughness length in analytical forms. The computed
results compared with those of Massman models (1987, 1997) show similarity with the present models. 相似文献
7.
This review introduces a novel method for modeling evapotranspiration and surface heat fluxes built on the theory of Maximum Entropy Production (MEP) as an application of the maximum entropy principle to non-equilibrium thermodynamic systems. The formulation of the MEP model uses the Bayesian probability theory, information theory through the concept of information entropy, and the similarity theory of the atmospheric boundary-layer turbulence. The MPE model provides simultaneous solution of latent, sensible and surface medium heat fluxes using only three input variables: net radiation, surface temperature and specific humidity. A unique feature of the MEP model is that the surface energy balance is closed at a range of space and time scales. The model does not require data of temperature and water vapor gradient, wind speed and surface roughness. It does not include empirical tunable parameters such as atmospheric and stomatal conductance. The MEP model is a promising new approach for the study of water and energy cycles of the Earth system across space-time scales. 相似文献
8.
精确估算地表蒸散一直是地球系统科学中的难点问题。经典的蒸散模型大多建立在水汽输送及能量平衡约束等基础上,相关的基础理论研究进展缓慢。最大熵增地表蒸散(E-MEP)模型是在综合借鉴贝叶斯概率论、信息熵概念、非平衡态热力学理论和大气边界层湍流相似性理论的基础上,建立的全新地表蒸散理论框架,克服了经典模型的主要缺陷,包括:离散梯度模型不满足能量守恒条件,Penman模型针对饱和土壤,Penman-Monteith模型需要率定经验参数等。E-MEP模型具有3个显著特点:①同时给出地表(包括水面、雪面和冰面)蒸散量、感热通量和介质表面热通量,且在所有时间空间尺度上满足能量平衡方程;②模型公式中没有可调经验参数,不依赖于温度梯度和水汽梯度变量,不需要输入风速和表面粗糙度;③适用于任何土壤含水量和植被覆盖条件。由于E-MEP模型建立在坚实的数学物理基础上,并具有解析表达式,简单易用,其输入变量和模型参数少于传统蒸散模型使用。地表辐射、表面温度、表面比湿等模型输入变量易于实地观测获取,且可通过遥感反演获得。检验分析表明,E-MEP模型优于Penman和Penman-Monteith等传统蒸散模型。这一全新的地表蒸散模型已被用于大尺度地表水热的遥感反演和过程监测,并用于改进气候模式的参数化方案。 相似文献
9.
大孔径闪烁仪研究区域地表通量的进展 总被引：15，自引：0，他引：15
地表湍流通量包括感热通量和潜热通量的准确测定对天气气候、农业、水文和水资源管理等意义重大。在几公里到几十公里尺度上有代表性的区域湍流通量的观测研究,特别在非均匀下垫面情况下,仍然非常困难。近年来蓬勃发展的大孔径闪烁仪（LAS）为这一问题的解决提供了全新手段。在介绍大孔径闪烁仪原理的基础上,综述了国内外利用大孔径闪烁仪开展区域地表通量观测研究的进展,包括在不同地表的LAS测量与涡动相关方法有关结果的对比,影响测量精度的关键因子分析,以及在区域地表通量遥感估算模型检验中的应用等,最后对大孔径闪烁仪的应用前景进行了展望。 相似文献
10.
A mathematical model has been developed to forecast or hindcast wind, waves, and longshore currents during the passage of a coastal storm. Storm intensity is a function of the barometric pressure gradient which is modeled by rotating an inverted normal curve around the center of an ellipse. The length and orientation of the major and minor axes of the ellipse control the size and shape of the storm. The path of the storm is determined by a sequence of storm positions for the hindcast mode, and by interpolated positions assuming constant speed and direction for the forecast mode. The site location, shoreline orientation, and nearshore bottom slope provide input data for the shore position. The geostrophic wind speed and direction at the shore site are computed from the latitude and barometric pressure gradient. The geostrophic wind is converted into surface wind speed and direction by applying corrections for frictional effects over land and sea. The surface wind speed and direction, effective fetch, and wind duration are used to compute wave period, breaker height, and breaker angle at the shore site. The longshore current velocity is computed as a function of wave period, breaker height and angle, and nearshore slope. The model was tested by comparing observed data for several coastal locations with predicted values for wind speed, wave period and height, and longshore current velocity. Forecasts were made for actual storms and for hypothetical circular and elliptical storms. 相似文献
11.
The problem of selecting the optimum operating frequency of a scatterometer, used for remote sensing of sea surface wind speed
has been addressed by applying the criteria of maximum sensitivity of backscattering coefficient to wind speed as well as
its correlation with wind speed. The backscattering coefficient values for sea surface were computed by the two-scale scattering
theory. To compute the atmospheric transmittance, 753 clear sky atmospheres over Indian Ocean were used. While the correlation
coefficient was uniform (0.94) throughout the frequency range of 1 to 30GHz, only frequencies above 5GHz were found sensitive
enough to yield a wind speed accuracy of ±2msec−1 and better, the accuracy improving with frequency. 相似文献
12.
The measurement of surface energy balance over a land surface in an open area in Bangalore is reported. Measurements of all
variables needed to calculate the surface energy balance on time scales longer than a week are made. Components of radiative
fluxes are measured while sensible and latent heat fluxes are based on the bulk method using measurements made at two levels
on a micrometeorological tower of 10m height. The bulk flux formulation is verified by comparing its fluxes with direct fluxes
using sonic anemometer data sampled at 10Hz. Soil temperature is measured at 4 depths. Data have been continuously collected
for over 6 months covering pre-monsoon and monsoon periods during the year 2006. The study first addresses the issue of getting
the fluxes accurately. It is shown that water vapour measurements are the most crucial. A bias of 0.25% in relative humidity,
which is well above the normal accuracy assumed by the manufacturers but achievable in the field using a combination of laboratory
calibration and field intercomparisons, results in about 20W m−2 change in the latent heat flux on the seasonal time scale. When seen on the seasonal time scale, the net longwave radiation
is the largest energy loss term at the experimental site. The seasonal variation in the energy sink term is small compared
to that in the energy source term. 相似文献
13.
14.
利用MODIS数据可见光波段、近红外波段和中红外波段,获得提取地表温度所需要的2个基本参数：地表比辐射率和大气透过率;然后对热红外波段b31、b32运用劈窗算法提取出陕北地区地表温度;并利用两种不同经验公式参数得出的结果与相应位置气象观测站观测的卫星过境时刻的地表气温进行比较。结果表明,劈窗算法简化模式能获得较准确的地表温度,符合陕北地区的实际地表状况,印证了应用该简化模式可以在大范围内快速实时监测地表温度。 相似文献
15.
基于SHAW模型的青藏高原唐古拉地区活动层土壤水热特征模拟 总被引：12，自引：9，他引：3
利用唐古拉综合观测场活动层及气象塔2007年的数据资料, 结合SHAW模型在3种不同地表反照率选取方案下进行模拟试验, 对唐古拉地区活动层土壤水热特征进行了单点数值模拟研究.通过观测值与3种模拟值的对比分析, 结果表明: SHAW模型能够较为好地模拟多年冻土区地表能量通量、 活动层土壤温度特征, 而对土壤含水量模拟不太理想, 但对其变化趋势模拟较好; 在模拟试验中, 模型输入参数地表反照率取1-12月各月平均地表反照率后, 模型对地表能量通量、 活动层土壤温度和湿度的模拟效果有了明显的提高; 而用一种地表反照率参数化方案的计算结果对模型输入参数进行修正后, 模型对活动层土壤温度和湿度的模拟效果有了明显的提高, 对地表能量通量的模拟效果提高不明显.总体上, SHAW模型对高原多年冻土区土壤冻融过程的模拟具有优势, 是研究高海拔多年冻土区活动层土壤水热过程较为理想的陆面模型. 相似文献
16.
北冰洋浮冰区近冰层湍流通量计算方法比较 总被引：8，自引：0，他引：8
利用2003年中国第二次北极科学考察获得的北冰洋浮冰区近冰层气象要素梯度观测资料,应用空气动力学的廓线法和总体输送法以及不同的普适函数,计算分析了2003年8月23日至9月4日浮冰区近冰层的摩擦速度、感热通量和潜热通量.结果表明:Holtslag普适函数的计算结果明显优于其它普适函数,总体输送法计算的不同层次湍流通量比廓线法更能够满足近冰层的常值通量层的假设,其结果可望为进一步优化北冰洋浮冰区边界层参数化方案和提高计算精度提供重要依据. 相似文献
17.
P. N. Mahajan R. M. Khaladkar S. G. Narkhedkar Sathy Nair P. C. Joshi P. K. Pal 《Journal of Earth System Science》2004,113(2):223-233
In this paper, daily variations of satellite-derived geophysical parameters such as integrated water vapour (IWV), cloud liquid
water content (CLW), sea surface temperature (SST) and sea surface wind speed (SSW) have been studied for a case of monsoon
depression that formed over the Bay of Bengal during 19th-24th August 2000. For this purpose, IRS P4 MSMR satellite data have
been utilized over the domain equator — 25‡N and 40‡-100‡E. An integrated approach of satellite data obtained from IRS-P4,
METEOSAT-5 and INSAT was made for getting a signal for the development of monsoon depression over the Indian region. Variations
in deep convective activity obtained through visible, infrared and OLR data at 06 UTC was thoroughly analyzed for the complete
life cycle of monsoon depression. Geophysical parameters obtained through IRS-P4 satellite data were compared with vorticity,
convergence and divergence at 850 and 200 hPa levels generated through cloud motion vectors (CMVs) and water vapour wind vectors
(WVWVs) obtained from METEOSAT-5 satellite. This comparison was made for finding proper consistency of geophysical parameters
with dynamical aspects of major convective activity of the depression.
From the results of this study it is revealed that there was strengthening of sea surface winds to the south of low-pressure
area prior to the formation of depression. This indicated the possibility of increase in cyclonic vorticity in the lower troposphere.
Hence, wind field at 850 hPa with satellite input of CMVs in objective analysis of wind field using optimum interpolation
(OI) scheme was computed. Maximum cyclonic vorticity field at 850 hPa was obtained in the region of depression just one day
before its formation. Similarly, with the same procedure maximum anticyclonic vorticity was observed at 200 hPa with WVWVs
input. Consistent convergence and divergence at 850 and 200 hPa was noticed with respect to these vorticities. In association
with these developments, we could get lowest values of OLR (120 W/m2 ) associated with major convective activity that was consistent with the maximum values of integrated water vapour (6-8gm/cm2) and cloud liquid water content (50-60 mg/cm2 ) persisting particularly in the southwest sector of the monsoon depression. 相似文献
18.
The measurement of metabolism using diel free-water oxygen techniques requires the estimation of atmospheric oxygen exchanges. We measured such exchange on nine different occasions in the freshwater, tidally-influenced Hudson River estuary using a floating dome technique. We also analyzed previously published data on the exchange of a variety of gases measured in lakes, estuaries, and open ocean waters using a wide variety of techniques. Data were expressed as a “transfer velocity” and normalized to an exchange of oxygen at 20°C. Considered together, these data indicate a significant predictive relationship when the natural log of transfer velocity is regressed with measured wind speed (r2 = 0.55; p = 0.0001). The influence of wind was particularly pronounced in estuaries and in lakes. Data from open-ocean waters showed much less influence of wind, probably because surface turbulence in these deeper waters can be temporally and spatially decoupled from wind. Our Hudson data agreed well with data collected in other systems. In general, data from estuaries—including the Hudson—indicated slightly higher transfer velocities at any given wind speed than do data from lakes (although this difference was less pronounced for our Hudson data than for other estuaries). The difference may result from some interaction of wind and tidal currents, or it may reflect a bias in the dome method of measurements; all of the estuarine data were collected using the dome approach, while the majority of the lake data were determined using an added tracer. If the dome method actually gives a biased, high estimate of oxygen flux, this is in contradiction to previous criticisms of this method that domes may underestimate fluxes by blocking wind at the water surface. We have used the regression of the natural log of transfer velocity versus wind speed developed here to estimate respiration in the Hudson estuary from diel changes in dissolved oxygen. To allow for possible biases in technique and for measurement error, we estimated 95% confidence limits around the regression. Estimates of respiration in the Hudson determined using the upper and lower 95% confidence limits are 30% higher and 12% lower than that determined when using the best-fit regression. An independently-constrained carbon budget for the tidally-influenced, freshwater Hudson River estuary indicates that respiration rates cannot be much higher than our mean estimate as calculated using the linear regression of the gas transfer and wind data to correct for air-water oxygen exchange. Gas transfer in natural systems is difficult to measure and is controlled by many interrelated physical factors. In the absence of extensive, system-specific field studies, the regression presented here should be useful in estimating atmospheric oxygen exchange in other estuarine or riverine ecosystems which are relatively deep and wide. 相似文献
19.
河套干旱地区夏季边界层结构特征观测分析 总被引：2，自引：0，他引：2
利用2013年夏季7月爱尔达K/LLX802J型机动式边界层风廓线雷达获取的三维风场资料和银川站高空气象探测资料,对河套干旱地区夏季边界层日变化特征进行了分析.结果表明:爱尔达K/LLX802J型机动式风廓线雷达能较好的反映并分辨出夏季河套干旱地区边界层内大气湍流和风场的演变过程.夏季7月河套干旱地区边界层高度白天平均为2127.2 m,夜间平均为1760.7 m,白天边界层高度比夜间平均高366.5 m.河套干旱区夏季地表非绝热加热对边界层的影响主要集中在800 m以下,800~2000 m高度边界层则主要受昼夜交替和大尺度天气系统的影响.夏季7月河套干旱地区边界层风速在300 m以下随高度增加而增大,离地500 m以下边界层易在北京时间07:00-11:00和18:00-21:00时段发生风速切变;300 m以下边界层白天盛行西南偏南风、夜间盛行南风,300~2000 m高度边界层白天和夜间均盛行东南风;离地300 m以下边界层易在夜间21:00-23:00时出现风向切变.夏季7月白天河套干旱地区边界层大气垂直速度在300 m高度以下随高度增加而增大,由0.3 m·s-1增大到0.6 m·s-1,夜间边界层大气垂直速度在200 m高度以下随高度增大而增大;300 m高度以上边界层大气垂直速度无论昼夜随高度变化均较小. 相似文献
20.
Barton剪切强度模型是目前工程实践中普遍采用的强度公式,而实践应用时,该模型中结构面粗糙性系数（JRC）的评估存在主观性和片面性的缺点。鉴于此,应用多重分形理论,提出了采用多重分形参数准确量化JRC的方法。首先应用数字图像处理技术获取了结构面三维形貌数据信息;然后采用投影覆盖法进行了结构面的分形维数计算,重点对结构面的多重分形特征进行了分析,通过对比分析了构造的15个结构面的多重分形特征值。结果表明：结构面越粗糙,多重分形特征参数 和 值越大, 或 能够很好地描述结构面的形貌特征。最后对9组石膏试件进行了剪切试验,通过不同正应力下对应的剪应力数据分析,结合结构面形貌多重分形参数 或 ,以Barton剪切强度公式为基础,应用最小二乘法原理,给出了JRC与 及JRC与 关系。这样在工程实际中,可以用参数 或 对JRC进行估算,克服了JRC人为估值主观性及采用二维标准轮廓线评估片面性的缺点,为准确评估结构面粗糙度提供了一条新的途径。在此基础上,应用Barton模型可准确估算岩体结构面的剪切强度。 相似文献