Horizontal Wind Components Research Articles

Added-Value of 3DVAR Data Assimilation in the Simulation of Heavy Rainfall Events Over West and Central Africa

This study aimed to evaluate the ability of a numerical weather prediction (NWP) model to capture the spatial distribution and magnitude of rainfall during three recent intense events (15–17 June 2011, and 23–25 August and 04–06 September 2012) observed over West and Central Africa, as well as the associated atmospheric and near-surface conditions. For each event, two numerical experiments were performed using the regional Weather Research and Forecasting (WRF) Model without (CNTL) and with (DA) data assimilation. Simulations were initialized using Global Forecast System data. The analyses were updated with the three-dimensional variational (3DVAR) technique using PrepBUFR and radiance observational data in a time window of ±3 h. The potential added value of data assimilation was addressed by comparing meteorological variables such as relative humidity, zonal and meridional wind components, 2 m temperature, and rainfall with the European Centre for Medium-Range Weather Forecasts reanalysis and the Tropical Rainfall Measuring Mission satellite-derived rainfall product datasets. WRF accurately simulated the spatiotemporal propagation and the zonally extended structure of rainfall as well as of relative humidity, 2 m temperature, and horizontal wind components. DA exhibited different biases, root mean square error, and spatial correlation, leading to mixed results in terms of outperforming CNTL. Results indicated that there was an increment in control variables, implying an added value from 3DVAR to the initial and boundary conditions. Rainfall forecasts were improved by 15–25 %. Uncertainties in the simulation of intense events in the study domain were noted, but improvement resulting from DA was limited due to lack of assimilated data for the region.

Correction of a Non-orthogonal, Three-Component Sonic Anemometer for Flow Distortion by Transducer Shadowing

Abstract We propose that flow distortion within a non-orthogonal CSAT3 sonic anemometer is primarily due to transducer shadowing, which is caused by wakes in the lee of the acoustic transducers impinging on their measurement paths. The dependence of transducer shadowing on sonic path geometry, wind direction and atmospheric stability is investigated with simulations that use surface-layer data from the Horizontal Array Turbulence Study (HATS) field program and canopy roughness-sublayer data from the CHATS (Canopy HATS) field program. We demonstrate the efficacy of correcting the CSAT3 for transducer shadowing with measurements of its flow distortion in the NCAR wind tunnel, combined with 6 months of data collected in the atmospheric surface layer with adjacent CSAT3 and orthogonal ATI-K sonic anemometers at the NCAR Marshall field site. CSAT3 and ATI-K measurements of the variance of vertical velocity $$\sigma _w^2$$ σ w 2 and the vertical flux of sonic temperature agree within 1 % after correction of both sonics for transducer shadowing. Both the simulations of transducer shadowing and the comparison of CSAT3 and ATI-K field data suggest a simple, approximate correction of CSAT3 surface-layer scalar fluxes with an increase on the order of 4–5 %, independent of wind direction and atmospheric stability. We also find that $$\sigma _w/u_*$$ σ w / u ∗ (where $$u_*$$ u ∗ is the friction velocity) and $$r_{uw}$$ r u w (the correlation coefficient) calculated with corrected CSAT3 data are insensitive to wind direction and agree closely with known values of these dimensionless variables for neutral stratification, which is evidence for the efficacy of the correction of the horizontal wind components for transducer shadowing as well.

Annual and semiannual harmonics of wind in the Northern stratosphere, mesosphere, and lower thermosphere

Based on the UK MetOffice gridded analysis in the altitudes from the tropopause to the mesopause of the Northern Hemisphere and the meteor radar observations in the mesosphere/lower thermosphere over Kazan (56°N49°E) and Collm (51°N13°E), the annual and semiannual harmonics of the horizontal wind components in the stratosphere, mesosphere, and lower thermosphere are studied for the period 2004–2013. The maxima of the amplitude of the annual harmonics of zonal wind are much more pronounced than the respective maxima for meridional wind. In contrast, the magnitudes of the maxima of the semiannual harmonics are comparable between zonal and meridional wind. The annual harmonics of horizontal wind in the studied layer typically reaches maximum in January–February. The semiannual harmonics of the components of horizontal wind in the stratosphere–lower thermosphere layer basically attains it first maximum in spring or in early summer. The results, included in the present paper, may be used for climate models validation.

Evaluation of wind profiles from the NERC MST radar, Aberystwyth, UK

Abstract. This study quantifies the uncertainties in winds measured by the Aberystwyth Mesosphere–Stratosphere–Troposphere (MST) radar (52.4° N, 4.0° W), before and after its renovation in March 2011. A total of 127 radiosondes provide an independent measure of winds. Differences between radiosonde and radar-measured horizontal winds are correlated with long-term averages of vertical velocities, suggesting an influence from local mountain waves. These local influences are an important consideration when using radar winds as a measure of regional conditions, particularly for numerical weather prediction. For those applications, local effects represent a source of sampling error additional to the inherent uncertainties in the measurements themselves. The radar renovation improved the signal-to-noise ratio (SNR) of measurements, with a corresponding improvement in altitude coverage. It also corrected an underestimate of horizontal wind speeds attributed to beam formation problems, due to pre-renovation component failure. The root mean square error (RMSE) in radar-measured horizontal wind components, averaged over half an hour, increases with wind speed and altitude, and is 0.8–2.5 m s−1 (6–12% of wind speed) for post-renovation winds. Pre-renovation values are typically 0.1 m s−1 larger. The RMSE in radial velocities is <0.04 m s−1. Eight weeks of special radar operation are used to investigate the effects of echo power aspect sensitivity. Corrections for echo power aspect sensitivity remove an underestimate of horizontal wind speeds; however aspect sensitivity is azimuthally anisotropic at the scale of routine observations (≈1 h). This anisotropy introduces random error into wind profiles. For winds averaged over half an hour, the RMSE is around 3.5% above 8 km, but as large as 4.5% in the mid-troposphere.

Observations of the scale-dependent turbulence and evaluation of the flux–gradient relationship for sensible heat for a closed Douglas-fir canopy in very weak wind conditions

Abstract. Observations of the scale-dependent turbulent fluxes, variances, and the bulk transfer parameterization for sensible heat above, within, and beneath a tall closed Douglas-fir canopy in very weak winds are examined. The daytime sub-canopy vertical velocity spectra exhibit a double-peak structure with peaks at timescales of 0.8 s and 51.2 s. A double-peak structure is also observed in the daytime sub-canopy heat flux co-spectra. The daytime momentum flux co-spectra in the upper bole space and in the sub-canopy are characterized by a relatively large cross-wind component, likely due to the extremely light and variable winds, such that the definition of a mean wind direction, and subsequent partitioning of the momentum flux into along- and cross-wind components, has little physical meaning. Positive values of both momentum flux components in the sub-canopy contribute to upward transfer of momentum, consistent with the observed sub-canopy secondary wind speed maximum. For the smallest resolved scales in the canopy at nighttime, we find increasing vertical velocity variance with decreasing timescale, consistent with very small eddies possibly generated by wake shedding from the canopy elements that transport momentum, but not heat. Unusually large values of the velocity aspect ratio within the canopy were observed, consistent with enhanced suppression of the horizontal wind components compared to the vertical by the very dense canopy. The flux–gradient approach for sensible heat flux is found to be valid for the sub-canopy and above-canopy layers when considered separately in spite of the very small fluxes on the order of a few W m−2 in the sub-canopy. However, single-source approaches that ignore the canopy fail because they make the heat flux appear to be counter-gradient when in fact it is aligned with the local temperature gradient in both the sub-canopy and above-canopy layers. While sub-canopy Stanton numbers agreed well with values typically reported in the literature, our estimates for the above-canopy Stanton number were much larger, which likely leads to underestimated modeled sensible heat fluxes above dark warm closed canopies.

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Organized structures in turbulent flow fields are a well-known and still fascinating phenomenon. Although these so-called coherent structures are obvious from visual inspection, quantitative assessment is a challenge and many aspects e.g., formation mechanisms and contribution to turbulent fluxes, are discussed controversially. During the “High Definition Clouds and Precipitation for Advancing Climate Prediction” Observational Prototype Experiment (HOPE) from April to May 2013, an advanced dual Doppler lidar technique was used to image the horizontal wind field near the surface for approximately 300 h. A visual inspection method, as well as a two-dimensional integral length scale analysis, were performed to characterize the observations qualitatively and quantitatively. During situations with forcing due to shear, the wind fields showed characteristic patterns in the form of clearly bordered, elongated areas of enhanced or reduced wind speed, which can be associated with near-surface streaks. During calm situations with strong buoyancy forcing, open cell patterns in the horizontal divergence field were observed. The measurement technique used enables the calculation of integral length scales of both horizontal wind components in the streamwise and cross-stream directions. The individual length scales varied considerably during the observation period but were on average shorter during situations with \(z/L<0\) compared to strongly stable situations. During unstable situations, which were dominated by wind fields with structures, the streamwise length scales increased with increasing wind speed, whereas the cross-stream length scales decreased. Consequently, the anisotropy increased from 1 for calm situations to values of 2–3 for wind speeds of 8–10\(\,\hbox {m s}^{-1}\). During neutral to stable situations, the eddies were on average quite isotropic in the horizontal plane.

Low-level jets and above-canopy drainage as causes of turbulent exchange in the nocturnal boundary layer

Abstract. Sodar (SOund Detection And Ranging), eddy-covariance, and tower profile measurements of wind speed and carbon dioxide were performed during 17 consecutive nights in complex terrain in northern Taiwan. The scope of the study was to identify the causes for intermittent turbulence events and to analyze their importance in nocturnal atmosphere–biosphere exchange as quantified with eddy-covariance measurements. If intermittency occurs frequently at a measurement site, then this process needs to be quantified in order to achieve reliable values for ecosystem characteristics such as net ecosystem exchange or net primary production. Fourteen events of intermittent turbulence were identified and classified into above-canopy drainage flows (ACDFs) and low-level jets (LLJs) according to the height of the wind speed maximum. Intermittent turbulence periods lasted between 30 and 110 min. Towards the end of LLJ or ACDF events, positive vertical wind velocities and, in some cases, upslope flows occurred, counteracting the general flow regime at nighttime. The observations suggest that the LLJs and ACDFs penetrate deep into the cold air pool in the valley, where they experience strong buoyancy due to density differences, resulting in either upslope flows or upward vertical winds. Turbulence was found to be stronger and better developed during LLJs and ACDFs, with eddy-covariance data presenting higher quality. This was particularly indicated by spectral analysis of the vertical wind velocity and the steady-state test for the time series of the vertical wind velocity in combination with the horizontal wind component, the temperature, and carbon dioxide. Significantly higher fluxes of sensible heat, latent heat, and shear stress occurred during these periods. During LLJs and ACDFs, fluxes of sensible heat, latent heat, and CO2 were mostly one-directional. For example, exclusively negative sensible heat fluxes occurred while intermittent turbulence was present. Latent heat fluxes were mostly positive during LLJs and ACDFs, with a median value of 34 W m−2, while outside these periods the median was 2 W m−2. In conclusion, intermittent turbulence periods exhibit a strong impact on nocturnal energy and mass fluxes.

The Impact of Targeted Dropwindsonde Observations on Tropical Cyclone Intensity Forecasts of Four Weak Systems during PREDICT

Abstract The value of assimilating targeted dropwindsonde observations meant to improve tropical cyclone intensity forecasts is evaluated using data collected during the Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) field project and a cycling ensemble Kalman filter. For each of the four initialization times studied, four different sets of Weather Research and Forecasting Model (WRF) ensemble forecasts are produced: one without any dropwindsonde data, one with all dropwindsonde data assimilated, one where a small subset of “targeted” dropwindsondes are identified using the ensemble-based sensitivity method, and a set of randomly selected dropwindsondes. For all four cases, the assimilation of dropwindsondes leads to an improved intensity forecast, with the targeted dropwindsonde experiment recovering at least 80% of the difference between the experiment where all dropwindsondes and no dropwindsondes are assimilated. By contrast, assimilating randomly selected dropwindsondes leads to a smaller impact in three of the four cases. In general, zonal and meridional wind observations at or below 700 hPa have the largest impact on the forecast due to the large sensitivity of the intensity forecast to the horizontal wind components at these levels and relatively large ensemble standard deviation relative to the assumed observation errors.

Short vertical-wavelength inertia-gravity waves generated by a jet–front system at Arctic latitudes – VHF radar, radiosondes and numerical modelling

Abstract. Inertia-gravity waves with very short vertical wavelength (λz≤1000 m) are a very common feature of the lowermost stratosphere as observed by the 52 MHz radar ESRAD (Esrange MST radar) in northern Scandinavia (67.88° N, 21.10° E). The waves are seen most clearly in radar-derived profiles of buoyancy frequency (N). Here, we present a case study of typical waves from 21 February to 22 February 2007. Good agreement between N2 derived from radiosondes and by radar shows the validity of the radar determination of N2. Large-amplitude wave signatures in N2 are clearly observed by the radar and the radiosondes in the lowermost stratosphere, from 9 km to 14–16 km height. Vertical profiles of horizontal wind components and potential temperature from the radiosondes show the same waves. Mesoscale simulations with the Weather Research and Forecasting (WRF) model are carried out to complement the analysis of the waves. Good agreement between the radar and radiosonde measurements and the model (except for the wave amplitude) shows that the model gives realistic results and that the waves are closely associated to the upper-level front in an upper-troposphere jet–front system. Hodographs of the wind fluctuations from the radiosondes and model data show that the waves propagate upward in the lower stratosphere confirming that the origin of the waves is in the troposphere. The observations and modelling all indicate vertical wavelengths of 700 ± 200 m. The radiosonde hodograms indicate horizontal wavelengths between 40 and 110 km and intrinsic periods between 6 and 9 h. The wave amplitudes indicated by the model are however an order of magnitude less than in the observations. Finally, we show that the profiles of N2 measured by the radar can be used to estimate wave amplitudes, horizontal wavelengths, intrinsic periods and momentum fluxes which are consistent with the estimates from the radiosondes.

Proposal of an empirical velocity spectrum formula in low‐wind speed conditions

Low‐wind spectra are investigated through the analysis of sonic anemometer observations gathered in three experimental campaigns: the Urban Turbulence Project, the NOrthern hemisphere climate Processed land‐surface EXperiment and the Graz experiment. From the comparison of the horizontal Eulerian experimental spectra computed in this work with those available in the literature it is shown that in low‐wind conditions the spectra present an evident peak in the lower frequency range, that it is not accounted for in the classical formulations. This is a consequence of the oscillatory behaviour of the horizontal wind, and the peak frequency depends on the meandering time‐scale of the horizontal wind components. In contrast with previous studies the meandering behaviour is observed in both stable and unstable conditions. A new formula for the low‐wind velocity spectrum is proposed and evaluated.

Temporal Evolution of Low-Level Winds Induced by Two-dimensional Mesoscale Surface Heat-Flux Heterogeneity

Using large-eddy simulation (LES), the effects of mesoscale local surface heterogeneity on the temporal evolution of low-level flows in the convective boundary layer driven by two-dimensional surface heat-flux variations are investigated at a height of about 100 m over flat terrain. The surface variations are prescribed with sinusoids of wavelength 32 km and varying amplitudes of 0, 50, 100, and 200 W m\(^{-2}\). The Weather Research and Forecasting numerical model is used as a mesoscale-domain LES model that has a grid spacing fine enough to explicitly resolve energy-containing turbulent eddies and a model domain large enough to include mesoscale circulations. Mesoscale circulations induced by the two-dimensional surface heterogeneity may undergo a flow transition and an associated spectral energy cascade, which has been found previously but only with one-dimensional surface heat-flux variations. Over a strongly heterogeneous surface prescribed with a two-dimensional sinusoid of amplitude 200 W m\(^{-2}\), the domain-averaged variance of the horizontal wind component initially grows rapidly, then undergoes a flow transition and subsequently rapidly decays. With a background wind, the induced mesoscale circulations are inhibited in the streamwise direction. However in the spanwise direction, somewhat stronger mesoscale circulations are induced, compared with those with no background wind. The background wind attenuates the significant reduction of the low-level temperature gradient by the fully-developed mesoscale horizontal flow. Spectral decomposition reveals that this rapid transition also exists in the mesoscale horizontal flows induced by the intermediate surface heterogeneity prescribed with a sinusoid of amplitude 100 W m\(^{-2}\). However the transition is masked by continuously growing turbulence.

Large-scale dynamical influence of a gravity wave generated over the Antarctic Peninsula – regional modelling and budget analysis

ABSTRACTThe case study of a mountain wave triggered by the Antarctic Peninsula on 6 October 2005, which has already been documented in the literature, is chosen here to quantify the associated gravity wave forcing on the large-scale flow, with a budget analysis of the horizontal wind components and horizontal kinetic energy. In particular, a numerical simulation using the Weather Research and Forecasting (WRF) model is compared to a control simulation with flat orography to separate the contribution of the mountain wave from that of other synoptic processes of non-orographic origin. The so-called differential budgets of horizontal wind components and horizontal kinetic energy (after subtracting the results from the simulation without orography) are then averaged horizontally and vertically in the inner domain of the simulation to quantify the mountain wave dynamical influence at this scale. This allows for a quantitative analysis of the simulated mountain wave's dynamical influence, including the orographically induced pressure drag, the counterbalancing wave-induced vertical transport of momentum from the flow aloft, the momentum and energy exchanges with the outer flow at the lateral and upper boundaries, the effect of turbulent mixing, the dynamics associated with geostrophic re-adjustment of the inner flow, the deceleration of the inner flow, the secondary generation of an inertia–gravity wave and the so-called baroclinic conversion of energy between potential energy and kinetic energy.

Aspects of Convective Boundary Layer Turbulence Measured by a Dual-Doppler Lidar System

Abstract Special designed dual-Doppler setups can be used to retrieve simultaneous measurements of two wind components with high temporal resolution in several heights throughout the atmospheric boundary layer. During a field campaign in summer 2011, different scan strategies were performed to demonstrate the opportunities of obtaining variance profiles of the vertical and horizontal wind components in complex terrain. A simplified error analysis reveals the effects of the error propagation of the uncorrelated noise of the single lidar systems. A comparison shows that the course of the derived horizontal wind component is in accordance to in situ measurements. The dual-Doppler vertical wind velocity reflects the up- and downdrafts in a convective boundary layer and is even able to reflect a light rain event. The normalized profiles of the vertical velocity variances reproduce the well-known decrease from about one-third of the boundary layer height to its top. The horizontal velocity variance did not reveal a systematic behavior on the considered days.

Windkanaluntersuchungen an einem frei gelüfteten Milchviehstall

The air exchange rate regulating the climate inside of natural ventilated livestock buildings is hard to determine in the field due to the variability of time and space of the dominant processes. Experiments in a wind tunnel laboratory can produce sound statistical and representative data obtained under controlled boundary conditions to complete data sets from the field. In this study, measurements of the horizontal wind components within a model of a natural ventilated barn were performed in the wind tunnel. The approach flow was chosen with low turbulence in order to gain knowledge on the influence of the installed equipment on the air flow. In fact, the measured profiles were influenced by the installed equipment and the feeding alley.

A novel approach to improve numerical weather prediction skills by using anomaly integration and historical data

Using the concept of anomaly integration and historical climate data, we have developed a novel operational framework to implement deterministic numerical weather prediction within 15 days. Real‐case validation shows pronounced improvements in the forecasts of global geopotential heights in 20 out of 30 cases with the Community Atmosphere Model version 3.0. Seven other cases are marginally improved, and only three are deteriorated, in which all are ameliorated within the first‐week period. The average of the 30 cases shows an obvious increase of anomaly correlation coefficient (ACC) and a decrease of root mean square error (RMSE) of the geopotential height over global, hemispherical, and tropical zones. Significant amelioration on tropical circulation is displayed within the first‐week prediction. The forecasting skill is extended by 0.6 day in terms of days of the ACC greater than 0.6 for 500 hPa 30 case averaged geopotential height on global scale. The 30 case mean ACC and RMSE of 500 hPa temperature show the increment of 0.2 and −1.6 K, respectively, in the first‐week prediction. In the case of January 2008, much more reasonable horizontal distribution and vertical structure are achieved in bias‐corrected model geopotential height, temperature, relative humidity, and horizontal wind components in comparison to reanalysis data. In spite of a need for additional storage of historical modeling data, the new method does not increase computational costs and therefore is suitable for routine application.

First observational study during a solar eclipse event on variations in the horizontal winds simultaneously in the troposphere-stratosphere-mesosphere-lower-thermosphere region over the equatorial station Thumba (8.5°N, 77°E)

The longest annular solar eclipse of the millennium occurred on 15 January, 2010, and was visible over the equatorial station Thumba (8.5°N, 77°E) around noon time. A host of experiments were carried out to study the variations due to the solar eclipse event on various geophysical parameters, from the Earth’s surface to ionospheric heights. The present study focuses on the variation in the horizontal winds in the height regions of 0–65 km and 80–100 km, using GPS-sondes, rocket-sondes and meteor wind radar. The observations were made during, and after, the maximum obscuration on the day of the eclipse, as well as at the same time on a control day. The observations showed a strengthening/weakening of winds along with directional changes both in zonal and meridional winds in the selected height domains. A drastic change from easterly to westerly is observed at 98 km during, and after, the maximum phase, but, for the meridional wind, the reversal is observed only after the maximum phase. Variations due to the eclipse were also observed around the tropopause and stratopause in both wind components. However, the observed changes in winds around the tropopause and stratopause could not be attributed unambiguously to the eclipse as day-to-day wind variability is not available in these height regions. The significance of the present study lies in reporting the variations in the horizontal wind components from the ground to the 100-km height region (with a gap around 65–80 km), and the characteristics of the atmospheric waves generated due to the mid-day annular solar eclipse.

Impact of Radiosonde Balloon Drift on Numerical Weather Prediction and Verification

Abstract Radiosonde observations employed in real-time numerical weather prediction (NWP) applications are disseminated through the Global Telecommunication System (GTS) using alphanumeric codes. These codes do not include information about the position and elapsed ascent time of the balloon. Consequently, the horizontal balloon drift has generally been either ignored or estimated in data assimilation systems for NWP. With the increasing resolution of atmospheric models, it is now important to consider the positions and times of radiosonde data in both data assimilation and forecast verification systems. This information is now available in the Binary Universal Form for the Representation of Meteorological Data (BUFR) code for radiosonde data. This latter code will progressively replace the alphanumeric codes for all radiosonde data transmitted on the GTS. As a result, a strategy should be adopted by NWP centers to deal with the various codes for radiosonde data during this transition. In this work, a method for estimating the balloon drift position from reported horizontal wind components and a representative elapsed ascent time profile are developed and tested. This allows for estimating the missing positions and times information of radiosonde data in alphanumeric reports, and then for processing them like those available in BUFR code. The impact of neglecting the balloon position in data assimilation and verification systems is shown to be significant in short-range forecasts in the upper troposphere and stratosphere, especially for the zonal wind field in the Northern Hemisphere winter season. Medium-range forecasts are also improved overall when the horizontal position of radiosonde data is retrieved.

Performance and Technique of Coherent 2-μm Differential Absorption and Wind Lidar for Wind Measurement

Abstract A coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) has been built with a high-power Q-switched Tm,Hm:YLF laser to measure CO2 concentration and radial wind speed. The performance of the Co2DiaWiL is described and analyzed, with a view to demonstrating system capabilities for remote measurements of wind velocities in the atmospheric boundary layer and free troposphere. Bias in the velocity measurements was estimated at −0.0069 m s−1 using measurements from a stationary hard target. The Co2DiaWiL achieved a velocity precision of 0.12 m s−1, derived from the magnitude of random error in radial wind velocity measurements. These measurements were made for ranges out to 20–25 km by using a horizontally fixed beam mode for average times of 1 min. Quantitative intercomparisons of 1-min averages between the Co2DiaWiL and a sonic anemometer revealed a correlation coefficient of 0.99. This study demonstrated measurements of horizontal wind profiles, by making radial wind velocity measurements with the Co2DiaWiL using conical scanning. Profile differences at higher levels could be attributed to probable large horizontal separations of the radiosondes and the low signal-to-noise ratio of the Co2DiaWiL. A pseudo-dual-Doppler technique was developed to retrieve horizontal wind components with a single-Doppler lidar and a steering mirror. Intercomparisons of the 1-min-averaged u and υ components from the pseudo-dual-Doppler lidar measurements with those from the sonic anemometer revealed correlation coefficients of 0.84 and 0.83, respectively.

Connecting Turbulence and Meandering Parameterization to Describe Passive Scalars Dispersion in Low Wind Speed Conditions

The following study deals with meandering of the horizontal mean wind. The main motivation for such investigation came from the difficulty in describing contaminant dispersion in meandering conditions. Observational field measurements point out that the autocorrelation function of the horizontal wind components, obtained for the meandering cases, displays an oscillating behavior with the presence of large negative lobes. Such negative lobes are described by an equation containing functions that represent patterns of movement associated to meandering and turbulence. As a consequence, this mathematical formulation connects the turbulence and meandering phenomenon establishing the employment of hybrid parameters in models that describe the meandering dispersion. Therefore, considering this dualistic aspect between meandering and turbulence manifestations, a new set of relations for the turbulence parameterization joined with the meandering of the wind have been developed and are available. This new turbulence parameterization for a stable shear forcing planetary boundary layer, united with a meandering mean time scale is able to describe contaminant meandering enhanced spread in a low wind speed stable planetary boundary layer.

Performance Analysis of Optimum Tilt Angle and Beam Configuration to Derive Horizontal Wind Velocities by Postset Beam Steering Technique

Software beam synthesis by postset beam steering (PBS) technique is used to derive the horizontal wind velocities from multireceiver phased-array radar data. In order to improve the efficiency of beam synthesis, the Capon beamforming method is used to synthesize time series signals in the desired line-of-sight angle within the radar transmit beam volume (3.6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> beamwidth). This paper describes beam synthesizing in optimum directions to reduce the error in the measurement of horizontal wind velocities using the PBS technique. For this purpose, beams are synthesized at various tilt angles with multibeam configuration. From the synthesized beam, power spectral distribution is obtained by one of the subspace methods, i.e., eigenvector (EV). The mean Doppler frequency and radial wind velocity at the desired line-of-sight angle are derived by an adaptive-moment estimation method from an EV-produced power spectrum. Using the moments obtained in various radial directions, horizontal wind components are derived by the conventional method for wind profiler radars. Also, an analysis is done for the required number of beams to improve PBS-based wind estimation. The statistical comparisons of performances of various tilt angles and beam configurations are being studied using the data collected from a multireceiver phased-array radar system (middle and upper atmosphere radar, Shigaraki, Japan). The analyzed results show that beam synthesis at the tilt angle from 1.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> to 2.0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> using a 16-beam configuration minimize the error in horizontal wind estimation by PBS technique.