Intercomparison of instruments for measurements of the atmospheric turbulence characteristics

In this paper, intercomparison testings of the Wind Master sonic anemometer manufactured by Gill Instruments Ltd. (U.K.) and two sonic anemometers manufactured by the Taifun Scientific Industrial Association (Obninsk, Russia), ATsAT-3M are described. Data of measurements of the standard deviations and spectrum characteristics of the vertical and horizontal wind speed components, heat and friction fluxes are presented. Dispersion of the measurements and degree of their coherence are characterized by the regression equation coefficients (a and b) and the cross-correlation coefficients. The coherence plot shows compliance of the measurements data throughout the entire frequency range.     

International turbulence comparison experiment (ITCE-81)

The main results of the International Turbulence Comparison Experiment (Tsimlyansk, U.S.S.R., June–July 1981) are presented. Groups from G.D.R., Poland, U.S.S.R., and Czechoslovakia took part in the experiment, while Bulgarian researchers were present as observers. A comparison of in situ measurements (by acoustic anemometers, thermoanemometers, and resistance thermometers) among themselves and with remote soundings (by sodars) was made. Simultaneous measurements of turbulent fluctuation characteristics and of wind velocity and temperature profiles were performed by different instruments. The results and temperature profiles were performed by different instruments. The results of these measurements were used to estimate the comparative accuracy of various models proposed for the evaluation of turbulent fluxes from profile data.     

An international turbulence comparison experiment (ITCE 1976)

Turbulence data for the International Turbulence Comparison Experiment (ITCE) held at Conargo, N.S.W. (35° 18′ S., 145° 10′ E.) during October, 1976 are analysed. The standard deviation % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikaiqado% hagaqbamaaCaaaleqabaGaaGOmaaaakiaacMcadaahaaWcbeqaaiaa% igdacaGGVaGaaGOmaaaaaaa!3B93!\[(s'^2 )^{1/2} \] and covariance % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG3bGbauaaceWGZbGbauaaaaaaaa!3809!\[\overline {w's'} \] measured by a number of instruments and instrument arrays have been compared to assess their field performance and calibration accuracy. Satisfactory agreement, i.e. typically 5% for % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikamaana% aabaGabm4CayaafaWaaWbaaSqabeaacaaIYaaaaaaakiaacMcadaah% aaWcbeqaaiaaigdacaGGVaGaaGOmaaaaaaa!3BA4!\[(\overline {s'^2 } )^{1/2} \] (except in humidity) and of the order of 20% for % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikaiqado% hagaqbamaaCaaaleqabaGaaGOmaaaakiaacMcadaahaaWcbeqaaiaa% igdacaGGVaGaaGOmaaaaaaa!3B93!\[(s'^2 )^{1/2} \], was achieved, but only after consideration of:

1. Instrumental response at high frequencies.
2. Flow distortion induced by instruments and supporting structures.
3. Spatial separation of instruments used for covariance measurements.
4. Statistical errors associated with single point measurements over a finite averaging time, and with lateral separation of two sensor arrays being compared.

     

三类测风仪测量近地层小尺度风场比较

用LSF1-1型测风仪测量一分钟一次瞬时风速记录分析表明,该测风仪可以粗略测量比较长周期的风速脉动变化,但精度较差。FL和Dyne测风仪由于它们灵敏度低,精度不够,不太合适测量小尺度风场的脉动变化。     

Aerosol remote sensing over land: A comparison of satellite retrievals using different algorithms and instruments

An inter-comparison study of the aerosol optical thickness (AOT) at 0.55 μm retrieved using different satellite instruments and algorithms based on the analysis of backscattered solar light is presented for a single scene over central Europe on October 13th, 2005. For the first time comparisons have been performed for as many as six instruments on multiple satellite platforms. Ten different algorithms are briefly discussed and inter-compared. It was found that on the scale of a single pixel there can be large differences in AOT retrieved over land using different retrieval techniques and instruments. However, these differences are not as pronounced for the average AOT over land. For instance, the average AOT at 0.55 μm for the area 7–12E, 49–53N was equal to 0.14 for MISR, NASA MODIS and POLDER algorithms. It is smaller by 0.01 for the ESA MERIS aerosol product and larger by 0.04 for the MERIS BAER algorithm. AOT as derived using AATSR gives on average larger values as compared to all other instruments, while SCIAMACHY retrievals underestimate the aerosol loading. These discrepancies are explained by uncertainties in a priori assumptions used in the different algorithms and differences in the sensor characteristics. Validation against AERONET shows that MERIS provides the most accurate AOT retrievals for this scene.     

A rapid-response 2-D drag anemometer for atmospheric turbulence measurements

A rapid response drag anemometer for measuring streamwise and lateral components of horizontal windspeed is described. Theory of operation, design and calibration are discussed with emphasis on the electronic preconditioning of signals and problems associated with using a mechanically resonant system as a sensor. Field comparisons showed half-hourly means and standard deviations of the streamwise component to be within 8% and 5% of respective values obtained from a 3-dimensional sonic anemometer. The lateral component from the drag anemometer was significantly more noisy than that from the 3-D sonic due to induced oscillations arising from vortex shedding. After mechanical and electronic filtering, half-hourly standard deviation comparisons agreed to within 6% for this component. Friction velocities obtained from the drag anemometer in combination with a 1-D sonic, agreed with measurements from the 3-D sonic anemometer to within 4% over a measured range of 0.05 to 1.2 m s^-1     

A precision kite or balloon-borne mini-sonde for wind and turbulence measurements

A highly mobile system for accurate measurements of wind speed and horizontal turbulence in the lowest few hundred meters of the atmosphere is presented. It consists of a light-weight sonde (only 50 g, including batteries that permit 12 h of continuous operation) which can be easily lifted by a small kite in winds below 5 m/s and up to at least 25 m/s. In winds below 5 m/s, a small kytoon may be used instead. The signals from the sonde are received by a standard FM-radio equipped with a frequency converter, and data are recorded on ordinary cassette tapes. Field tests against towermounted precision instruments were performed at two sites during neutral and unstable conditions with the sonde suspended 25 m below a small kite, the measuring heights being 11 and 18 m respectively during the two test series. Mean wind speeds are found to be accurate to within ±0.2 m/s. Wind speed spectra obtained with the flying sonde can be evaluated up to 0.5 Hz and are found to agree closely with the spectra of the longitudinal component recorded simultaneously by the tower-mounted instrument at the same height. After correction for high frequency loss, which amounted to 5% at this low height (it is expected to decrease rapidly with height), the standard deviation of the wind recorded by the sonde agreed to within 2% with that obtained by the reference instrument. A notable result of the field tests is that there was no sign of degradation of the performance of the sonde in strong turbulence conditions.     

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.     

Simultaneous measurements of turbulence over land and water

Turbulence and mean flow variables under unstable conditions are examined with special emphasis on the consequences of roughness and surface elevation change. An interpolation formula for _w ², between neutral and free convection, is shown to bring order to the data. The spectral distribution of vertical wind variance is found to be in good agreement with results over horizontal homogeneous terrain, both with respect to form and position. In particular, the length scale _m corresponding to the maximum of nS _w(n) is unchanged. Another turbulent length scale, (k/)z, is found to be substantially reduced in the disturbed zone of the internal boundary layer. To a first approximation, the flow-acceleration effect on the non-dimensional wind shear can be separated from the diabatic effect.     

A Loop Current experiment: Field and remote measurements

An overview of a new comprehensive observational study of the Loop Current (LC) in the eastern Gulf of Mexico that encompassed full-depth and near-bottom moorings, pressure-equipped inverted echo sounders (PIES) and remote sensing is presented. The study array was designed to encompass the LC from the Campeche Bank to the west Florida escarpment. This overview centers about principal findings as they pertain to mesoscale dynamics. Two companion papers provide in-depth analyses. Three LC anticyclonic eddy separation events were observed with good 3D spatial coverage over the 2½ year extent of the field study; the three separations exhibited similar processes after the LC had extended into the eastern Gulf. Large scale (∼300 km wavelength, 40–60 day periods) southward propagating meanders developed on the eastern side of the LC over deep (∼3000 m) water that were the result of baroclinic instability between the upper layer meandering jet and lower layer cyclones and anticyclones. The lower layer was only highly energetic during relatively short (∼2–3 months) intervals just prior to or during eddy detachments because of baroclinic instability. The steepening of the meanders lead to a pinch-off of LC eddies. The deep lower-layer eddies, constrained by the closed topography of the southeastern Gulf, propagated westward across the detachment zone and appear to assist in achieving separation. Small scale (∼50–100 km, periods ∼10 days) frontal eddies, observed on the western side of the LC along the Campeche Bank slope, decay over the deep water of the northern part of an extended LC, and have little influence on lower layer eddies, the east side meanders and the eddy detachment processes.     

Impacts of cloud and turbulence schemes on integrated water vapor: comparison between model predictions and GPS measurements

Summary Structures in atmospheric Integrated Water Vapor (IWV) have been studied for the three successive cyclones, Kerstin, Liane and Monika, which controlled the meteorological conditions in the Baltic Sea catchment region in the period from 28 August to 5 September 1995 (part of the PIDCAP observational campaign defined within BALTEX). Several model predictions of these cyclones have been performed with a regional atmospheric general circulation model (RACMO). The impact of two different versions of the model physics package (standard ECHAM4 and a revised version with modifications in the cloud and turbulence scheme) has been investigated. Model predicted IWV has been evaluated with GPS station data from several stations in Sweden and Finland. For the most strongly developed cyclone Monika, the revised scheme generates more pronounced IWV structures, with well defined bands of high and low values of IWV curving into the center of the cyclone. In particular, the shape of the minima are in better agreement with the GPS station data, and the consistency between two subsequent model forecasts is also larger with the revised physics package. For the weaker systems, Kerstin and Liane, results from both model versions are very similar. Received August 11, 2000 Revised February 13, 2001     

A comparison of some aerodynamic resistance methods using measurements over cotton and grass from the 1991 California ozone deposition experiment

Measurements of dry, deposition velocities (V _d ) of O₃ (using the eddy correlation technique) made over a cotton field and senescent grass near Fresno California during July and August 1991 were used to test some dry deposition velocity models. Over the cotton field, the observed maximum daytimeV _d was about 0.8 cm s^–1 and the average nighttime value was about 0.2 cm s^–1. Over the grass, daytime values averaged about 0.2 cm s^–1 and nighttime values about 0.05 cm s^–1. Application of a site-specific model known as ADOM (Acid Deposition and Oxidant Model) over the cotton field generally overestimated the observations except for a few hours in the afternoon when the observations were underestimated The overestimation was attributed to inadequacies in the surface resistance formulation and the underestimation to uncertainties in the aerodynamic formulation. Unlike previous studies which focused on the role of surface resistance, we perform additional tests using a large variety of aerodynamic resistance formulae, in addition to those in ADOM, to determine their influence on the modelledV _d of O₃ over, cotton. Over grass, ADOM considerably overestimated the observations but showed improvement when other surface resistance formulations were applied.     

A comparison between transilient turbulence theory and the exchange coefficient model approaches

The transilient turbulence model of Stull and Driedonks (1987) and the exchange coefficient model of Bougeault and Lacarrère (1989) are intercompared on four convective days of the HAPEX-MOBILHY experiment. We show that the numerical formulations of the models are very close to each other, despite their totally different theoretical backgrounds. Both models describe the mixing effect of the turbulence via matrices having the same general characteristics. The results of the models are also found to be very similar in general, although the transilient approach requires more computations. Some systematic differences are noted and discussed in detail. We argue that similar work should be conducted on non-convective cases before deciding on the superiority of one or the other approach.     

Aircraft measurements of boundary-layer turbulence over the central Equatorial Pacific Ocean

We analyze gust probe measurements obtained in the convective boundary layer over the central equatorial Pacific as part of the Equatorial Pacific Ocean Climate Studies (EPOCS) program. From the lowest level flights, the bulk transfer coefficients are found to be 1.1 × 10^-3 and 1.4 × 10^-3 for latent and sensible heat fluxes, respectively. Vertical profiles of water vapor density, potential temperature and wind velocity are obtained as are the profiles of the fluxes of latent and sensible heat and momentum. From the extrapolated profiles, we obtain surface fluxes of 120 W m^-2 and 13 W m^-2 for latent and sensible heat, respectively, and 0.11 N m^-2 for momentum. The 10 m drag coefficient is 1.5 × 10^-3. Two convergence boxes, north and south of the ITCZ, are analyzed. Enhanced convergence is found in the northern trades relative to the southern trades. The advective acceleration is found to be comparable in magnitude to the other terms in the horizontal equations of motion.     

基于三台测风激光雷达的大气湍流和三维风场研究

为了获取大气湍流和空间三维风场结构,利用3台同型号的测风激光雷达开展协同观测试验。(1)利用虚拟铁塔协同观测技术开展大气湍流探测,与香河102 m铁塔安装的三维超声风速仪观测结果做对比,32 m处高频(10 Hz)风速的相关系数高达0.92,平均误差为0.77 m/s,均方根误差为0.41 m/s;大气湍流强度(TKE)的相关系数高达0.99,平均误差为-0.02 m²/s²,均方根误差为0.08 m²/s²,并且协同观测的高频风速与三维超声风速仪的观测结果具有相同的频谱结构。(2)利用扫描协同观测技术开展三维风场探测,与铁塔上的常规测风设备相比,其90 m高度处的水平风速和风向的相关系数分别为0.92和0.93,平均误差为-0.41 m/s和0°,均方根误差为0.73 m/s和34°。相比于单台测风激光雷达,基于3台测风激光雷达协同观测技术具有一定的优势:不需要风场水平均匀的假设、探测精度更高等。但其对观测环境的要求较高:观测路径上不能有遮挡、观测必须协同等。在科研业务应用中,需要根据实际的观测需...     

Intercomparison of instruments for tropospheric measurements using differential optical absorption spectroscopy

The results of an intercomparison campaign of eight different long path UV-visible DOAS instruments measuring NO₂, O₃ and SO₂ concentrations in a moderately polluted urban site are presented. For effective optical path lengths of 230 and 780 m the overall spread of these measurements (±1) are 5×10¹⁰, 6×10¹⁰ and 1×10¹⁰ molec·cm^-3 (2.0, 2.4, and 0.4 ppb) for these molecules respectively when all instruments used a common set of absorption cross sections. The remaining differences are not completely random and the systematic differences are attributed to the different retrieval methods used for each instrument.     

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.