A note on estimating the effect of a limited fetch on micrometeorological evaporation measurements

A formula for the effective fetch of micrometeorological evaporation measurements is derived by application of diffusion theory, using Calder's approximation of a uniform wind field and neutral atmospheric stability. This simplification allows estimation of the likely sampling error, which would result from an upwind step-change in evaporation rate, without change in roughness.     

Determining carbon isotope signatures from micrometeorological measurements: Implications for studying biosphere–atmosphere exchange processes

In recent years considerable effort has been focused on combining micrometeorological and stable isotope techniques to partition net fluxes and to study biosphere–atmosphere exchange processes. While much progress has been achieved over the last decade, some new issues are beginning to emerge as technological advances, such as laser spectroscopy, permit isotopic fluxes to be measured more easily and continuously in the field. Traditional investigations have quantified the isotopic composition of biosphere-atmosphere exchange by using the Keeling two-member mixing model (the classic Keeling plot). An alternative method, based on a new capacity to measure isotopic mixing ratios, is to determine the isotope composition of biosphere–atmosphere exchange from the ratio of flux measurements. The objective of this study was to critically evaluate these methods for quantifying the isotopic composition of ecosystem respiration (δ_R) over a period of three growing seasons (2003–2005) within a heterogeneous landscape consisting of C₃ and C₄ species. For C₄ canopies, the mixing model approach produced δ_R values that were 4–6‰ lower (isotopically lighter) than the flux-gradient method. The analyses presented here strongly suggest that differences between flux and concentration footprint functions are the main factor influencing the inequality between the mixing model and flux-gradient approaches. A mixing model approach, which is based on the concentration footprint, can have a source area influence more than 20-fold greater than the flux footprint. These results highlight the fact that isotopic flux partitioning is susceptible to problems arising from combining signals (concentration and fluxes) that represent very different spatial scales (footprint). This problem is likely to be most pronounced within heterogeneous terrain. However, even under ideal conditions, the mismatch between concentration and flux footprints could have a detrimental impact on isotopic flux partitioning where very small differences in isotopic signals must be resolved.     

Applying single and two layer canopy models to derive conductances of a Scots pine plantation from micrometeorological measurements

Summary A single layer (Penman-Monteith) and a two layer (modified Shuttleworth-Wallace) evapotranspiration (ET) model are used alternatively to derive conductances related to the dominant fluxes of water vapor from a semi-closed Scots pine plantation. The derivations are based on micrometeorological measurements of above canopy energy flux densities and a simple resistance network. For a period of consecutive fine weather days, below canopy net radiation and below canopy ET were about 20 percent of the corresponding above canopy values. Resulting conductances for latent heat flux agreed well with porometric measurements of pines and understory scaled to canopy level. The shift from single to two layer modelling reduced the canopy conductance to pine conductance by the fraction of understory ET.However, characteristics of porometer results and micrometeorologically derived conductances were quite different: The porometer estimates of conductance were highly variable due to stomatal response to local environmental conditions or natural variability within the tree canopy and vegetation patches which characterized the forest understory. Micrometeorologically derived conductances integrate spatially resulting in relatively smooth and repetitive daily patterns that lack the information of small scale variability. This is seen as a favorable feature of micrometeorological derived conductances when used for the parameterization of atmospheric models for climate research as long as small scale bio-diversity is irrelevant.With 5 Figures     

Some results in studies of meteorological reagents

Summary The Yugoslavian hail-suppression system uses rockets with 0.4 kg of a pyrotechnical mixture which produces an AgI based aerosol by the process of burning. The activity of thus obtained aerosol is measured in several type cold chambers.Presented results were obtained at the Hydrometeorological Institute of Croatia (HIC), Zagreb, for the pyrotechnical mixtures R-32 (used from 1981 to 1988), VTG-8 (1986–1988), MKM-10 (used in 1989) and AJ (it will be used in year 1989).The activity of aerosol depends on several parameters, e.g. the type of burning and streaming, meteorological conditions and the time the aerosol remains in the cloud. Furthermore, the activity depends on the technological production process of the pyro-technical mixtures.The pyro-technical mixtures MKM-10 and AJ proved to be more active than the R-32 and VTG-8 in the interval from the threshold to –10°C, i.e. in the warm cloud area.

---

Zusammenfassung Das jugoslawische Hagelabwehrsystem verwendet Raketen mit 0.4 kg eines pyrotechnischen Präparats, das bei Verbrennung Aerosole auf AgJ-Basis freisetzt. Die Wirkung dieser Aerosole wird in unterschiedlichen Typen kalter Nebelkammern gemessen. Die im Hydrometeorologischen Institut von Kroatien (HIC) in Zagreb erzielten Ergebnisse beziehen sich auf die pyrotechnischen Mischungen R-32 (in Verwendung von 1981 – 1988), VTG-8 (1986 – 1988), MKM-10 (1989) und AJ (wird erst 1989 verwendet).Die Wirkung des Aerosols ist von verschiedenen Parametern abhängig, so etwa von der Art der Verbrennung und der Strömung, von den meteorologischen Bedingungen und von der Verweildauer des Aerosols in der Wolke. Weiters hängt sie auch vom technischen Herstellungsprozeß der pyrotechnischen Mischung ab.Die pyrotechnischen Präparate MKM-10 und AJ haben sich im Intervall vom Gefrierpunkt bis –10°, also in den warmen Wolkenzonen, als wirksamer erwiesen als R-32 und VTG-8.

---

---

With 8 Figures     

A micrometeorological investigation of surface exchange parameters over heathland

An automated system for measuring the dry deposition fluxes of SO₂ on a routine basis based on the micrometeorological gradient technique has been developed for application over grassland and other short vegetation. The ability of the system to determine turbulent exchange parameters such as the friction velocity u _* and the heat flux H was investigated by comparison with an automated eddy correlation system.Determinations of u _* and H by both methods have generally been found to be in very good agreement for 20 min averages. Aerodynamic resistances derived from both systems showed no systematic differences but individual values differed considerably. From the analysis it appeared that in addition to classical rejection criteria on wind speed and inhomogeneity, etc., periods with large shifts in wind direction also have to be removed from the data set before interpretation.     

A model of the ground surface temperature for micrometeorological analysis

Micrometeorological models at various scales require ground surface temperature, which may not always be measured in sufficient spatial or temporal detail. There is thus a need for a model that can calculate the surface temperature using only widely available weather data, thermal properties of the ground, and surface properties. The vegetated/permeable surface energy balance (VP-SEB) model introduced here requires no a priori knowledge of soil temperature or moisture at any depth. It combines a two-layer characterization of the soil column following the heat conservation law with a sinusoidal function to estimate deep soil temperature, and a simplified procedure for calculating moisture content. A physically based solution is used for each of the energy balance components allowing VP-SEB to be highly portable. VP-SEB was tested using field data measuring bare loess desert soil in dry weather and following rain events. Modeled hourly surface temperature correlated well with the measured data (r ² = 0.95 for a whole year), with a root-mean-square error of 2.77 K. The model was used to generate input for a pedestrian thermal comfort study using the Index of Thermal Stress (ITS). The simulation shows that the thermal stress on a pedestrian standing in the sun on a fully paved surface, which may be over 500 W on a warm summer day, may be as much as 100 W lower on a grass surface exposed to the same meteorological conditions.     

Some experimental results from studies of air-sea interactions

A brief review is given of some of the results of studies of air-sea interactions carried out at the Institute of Water Problems (Moscow) over the last 2 decades.     

Calibration and performance evaluation of a lightweight propellor anemometer for micrometeorological research

The results of calibrations of the airspeed measurement, distance constant and cosine response for a sensitive propellor (vane) anemometer are described. A triad of these anemometers may be used to measure wind velocity, and the estimated uncertainty in this measurement is evaluated for a typical triad and a range of wind directions.The propellor anemometers tested provide sensitivity similar to that of sonic anemometers for research, but at much lower cost (although for a narrower range of wind conditions). Large arrays of the anemometers allow the spatial and temporal structure of wind turbulence to be measured directly. The anemometers have been used for several years, and are robust enough for micrometeorological research.     

Comparison of different boundary layer surface schemesusing single point micrometeorological field data

Summary  In the last decade, a vast number of land surface schemes has been designed for use in global climate models, atmospheric weather prediction, mesoscale numerical models, ecological models, and models of global changes. Since land surface schemes are designed for different purposes they have various levels of complexity in the treatment of bare soil processes, vegetation, and soil water movement. This paper is a contribution to a little group of papers dealing with intercomparison of differently designed and oriented land surface schemes. For that purpose we have chosen three schemes for classification: i) global climate models, BATS (Dickinson et al., 1986; Dickinson et al., 1992); ii) mesoscale and ecological models, LEAF (Lee, 1992) and iii) mesoscale models, LAPS (Mihailović, 1996; Mihailović and Kallos, 1997; Mihailović et al., 1999) according to the Shao et al. (1995) classification. These schemes were compared using surface fluxes and leaf temperature outputs obtained by time integrations of data sets derived from the micrometeorological measurements above a maize field at an experimental site in De Sinderhoeve (The Netherlands) for 18 August, 8 September, and 4 October 1988. Finally, comparison of the schemes was supported applying a simple statistical analysis on the surface flux outputs. Received November 23, 1999 Revised August 18, 2000     

Some preliminary results on pilot study of global change in China

On the basis of existing data and research results the changes of life supporting environment in China in the his-tory are briefly described. The differences between regional climate variations and climate jump are the very impor-tant features and phenomena in estimating the trend of environmental evolution in the future. Finally, it is pointed out that sensitive zone is an ideal place to study global change. Many evidences show that the response of environmental elements in the sensitive zones to global change events is very obvious, so that much attention should be paid to the study of sensitive zone.     

Some methodological questions concerning advection measurements: a case study

A dataset from two campaigns conducted at the Vielsalm experimental site in Belgium was used as a basis for discussing some methodological problems and providing intermediate results on estimating CO₂ advection. The analysis focused on the horizontal [CO₂] gradient and on the vertical velocity w, the variables most affected by uncertainty. The sampling error for half-hourly horizontal [CO₂] gradients was estimated to be 1.3 μmol mol⁻¹. Despite this important random error for half-hour estimations of [CO₂], the mean horizontal [CO₂] gradients in advective conditions were shown to be representative at the ecosystem scale and to extend only to the lowest part of a drainage sub-layer, which developed in the trunk space. By contrast, under daytime conditions, this gradient was shown to be more sensitive to local source heterogeneities. The estimation of the short-term averaged vertical velocity ( was the greater source of error when computing advection terms. The traditional correction methods used to obtain are discussed and a (co)sine correction is tested to highlight the instrumental origin of the offset in w. A comparison of measurements by sonic anemometers placed close together above the canopy showed that the uncertainty on was 0.042 m s⁻¹, which is of the same order of magnitude as the velocity itself. In addition, as the drainage sub-layer is limited to the lowest part of the canopy, the representativeness of is questionable. An alternative computation using the divergence of the horizontal wind speed in the trunk space produced a estimation that was four times lower than the single-point measurement. However, this value gives a more realistic estimate of the vertical advection term and improves the CO₂ budget closure at the site.     

Phase-averaged results of wave-follower measurements of turbulent shear flow above water waves

Average air velocities and turbulent Reynolds stresses were calculated at fixed heights above 1 Hz progressive sinusoidal water waves by reanalyzing the experimental data of Chao and Hsu (1978).     

Evaporation from the desert: Some preliminary results of HEIFE

As part of a feasibility study for HEIFE, a Sino-Japanese Cooperative Research Program on Atmosphere-Land Surface Processes in Heihe River Basin, fluxes of water vapour are estimated above and below the sand surface. It is found that during the daytime under clear skies, the water vapour flux is directed towards the surface from both the atmosphere above and the sand below.     

Some limitations to measurements of turbulence micro-structure with hot and cold wires

Some of the problems associated with measurements of the small-scale characteristics of dynamic and thermal fully developed turbulence are considered in the context of a study of the tendency-towards-isotropy assumption, Taylor's hypothesis, and internal intermittency, taking advantage of the possibilities offered by the I.M.S.T. Air-Sea Interaction Simulation Tunnel. The paper reviews and discusses the choices of probes and operating parameters for hot-wire anemometers and cold-wire thermometers. A detailed study of the most important characteristic, the spectral signal-to-noise ratio, is presented. Problems specific to measurements with several wires are studied, especially the true resolution of one-point multi-wire probes and the errors due to calibration uncertainties for two-point measurements. Serious doubts are raised on the validity of gradient-probe data.     

The influence of stratification on heat and momentum turbulent transfer in antarctica

Data from the Antarctic winter at Halley Base have been used in order to evaluate qualitatively and quantitatively how the stratification in the low atmosphere (evaluated with the gradient Richardson number, Ri) influences the eddy transfers of heat and momentum. Vertical profiles of wind and temperature up to 32 m, and turbulent fluxes ( , and ) measured from three ultrasonic thermo-anemometers installed at 5, 17 and 32 m are employed to calculate Ri, the friction velocity (u _*) and the eddy diffusivities for heat (K _h ) and momentum (K _m ). The results show a big dependence of stability onK _m ,K _h andu _*, with a sharp decrease of these turbulent parameters with increasing stability. The ratio of eddy diffusivities (K _h /K _m ) is also analyzed and presents a decreasing tendency as Ri increases, reaching values even less than 1, i.e., there were situations where the turbulent transfer of momentum was greater than that of heat. Possible mechanisms of turbulent mixing are discussed.     

青藏高原东坡理塘地区近地层湍流通量与微气象特征研究

简要介绍青藏高原东坡理塘大气综合观测站长期观测试验,并利用2006年1、7月资料分别代表该站冬季和夏季,初步分析和比较该地区冬、夏季近地层微气象特征和湍流通最输送情况,得到了以下结论:(1)风、温、湿均表现出明显的日变化特征.冬季风速值平均大于夏季,风速极大值均出现在下午;冬季温度梯度早晚大,白天小,而夏季均较小;湿度梯度早晚大于白天.(2)中件条件下风速廓线对数关系表现为一条直线而非中件条件下略偏离对数关系,晚上均有逆温现象出现.在一定高度能观测到较弱的逆湿现象.(3)冬季以感热为主,潜热值较小,夏季以潜热为主,但感热也较大,且冬季通量值要远小于夏季;冬季动量通量平均大于夏季,二氧化碳通量远小于夏季;浅层(地面以下2和5 cm)土壤热通量也具有明显的日变化特征,白天从土壤吸收热量,夜间则放出热量.(4)地面热源强度具有显著的日变化特征:白天为强热源,夜间冷热源特征不明显.冬季和夏季全天平均表现为热源,但夏季强度远大于冬季,平均达到134 W/m2左右,冬季仪约35.3 W/m2.     

Some results of activities on the improvement of weather conditions over metropolises

Some results of activities on cloud seeding operations to modify the weather conditions over metropolises are given. The main objective of these activities was to dissipate the clouds and to decrease or to stop the precipitation on the territory under protection during the political, cultural, or sporting events. Up to 12 aircraft specially equipped with the measuring equipment needed to carry out the cloud seeding, with the Land-Aircraft-Land radio data transmission system, and with the cloud seeding means were used to fulfill the works on the weather modification. The liquid nitrogen, “dry ice”, silver iodide, and coarse-dispersion powder were used as the reagents for the cloud seeding. To control the aviation works and the results of the cloud seeding, the ground-based automated meteorological radar systems were used. The results of more than 40 large-scale operations on the improvement of weather conditions carried out since 1995 in different regions of Russia and near abroad indicate the efficiency of the methods and technical means of cloud seeding developed by the specialists of Roshydromet to modify the atmospheric precipitation.