Radar interferometry technique: Three‐dimensional wind measurement theory

Numerous workers across various industries, from construction and transportation to agriculture and emergency response, face harsh working environments characterized by cold temperatures and intense winds. These conditions present serious health and safety risks, which may result in hypothermia. Although established standards, such as ISO 11092, are crucial in measuring the thermal resistance of textile assemblies, an essential factor is often overlooked: the influence of wind speed and direction. In this context, this article aimed to address this gap in current knowledge by investigating the effects of wind on the thermal resistance of nonwoven textile assemblies, to develop a more effective protective clothing system for harsh environments. This study investigated the effect of horizontal and vertical wind speeds on the thermal resistance of a technical bio-based nonwoven assembly, composed of milkweed, kapok and polylactic acid, aiming to understand how forced convection influences heat transfer in real-world conditions. Three samples (A, B, and C) were tested under wind speeds ranging from 0 to 4 m·s −1 , and their thermal resistance was measured in both horizontal and vertical wind directions. Results showed that increasing wind speed consistently decreased thermal resistance for all samples. Vertical wind demonstrated a more pronounced effect, with reductions in thermal resistance reaching 81% for Sample C compared to 51% under horizontal wind. Comparison of experimental and theoretically predicted thermal resistance values using the models presented in the ISO 9920 standard, indicated significant discrepancies.

Measurements of the horizontal and vertical wind component by a crosswind scintillometer during foehn, the chinooklike downslope windstorm in the Alps, are presented. Because of the sparsity of vertical velocity measurements in the immediate vicinity, the scintillometer calibration is checked mainly with horizontal wind measurements. Then it is assumed that the calibration is the same for both components. The concept was tested during the Mesoscale Alpine Programme field campaign in the autumn of 1999, during which two scintillometers were deployed. Strong, long-lasting, quasi-stationary downward motions on the order of 5 m s^-1 and horizontal wind speeds of over 30 m s^-1 were detected during strong foehn phases within the valley. Aircraft measurements of various transects near the light paths are compared with two crosswind evaluation techniques. One of them, the slope method, tends to overestimate the actual wind speed by about 20%, whereas the peak technique gives values that are about 10% too low for high wind speeds. The peak method also fails to measure meaningful vertical crosswind speeds. The scintillometer data of one particular foehn storm are compared with nearby Doppler lidar data. The agreement of the horizontal measurements is reasonable. Discrepancies are attributed to topographic and dynamic effects that cause significant spatial inhomogeneities in the wind field. The applicability of continuous scintillometer vertical crosswind measurements in mountainous terrain is demonstrated.

Computer simulations of a Boeing 727 class aircraft landing in turbulence were developed by programming the longitudinal aircraft equations of motion into a digital computer with various input values of vertical and horizontal wind speeds. Turbulent wind data was fed to the computer in one-second intervals. The computer computed in one-second intervals the aircraft speed, altitude, horizontal distance traveled, rate-of-descent, pitch attitude, glide path angle (from edge of runway) and elevator angle. All computer runs were made in the 'stick-fixed' mode. The RMS values of altitude and velocity perturbations (from equilibrium) were found to be large when horizontal wind gusts had sinusoidal components at or near the phugoid (long period) frequency. Maximum RMS altitude deviations occurred when the vertical wind had sinusoidal components which were 1/10 to 1/5 of the phugoid frequency. When real wind data (obtained from NCAR Queen Air) were used as input winds good correlations were found to exist between RMS velocity perturbations and both horizontal and vertical wind shears.

Data obtained by the Neutral Atmosphere Composition Spectrometer (NACS) and the Wind and Temperature Spectrometer (WATS) instruments on Dynamics Explorer 2 (DE 2) show examples of large wave‐like events in composition, vertical wind, and temperature, particularly (perhaps almost exclusively) at high geomagnetic latitudes. These events are believed to arise due to atmospheric gravity waves (AGWs). If so, the various perturbation quantities of mass density, pressure, temperature, horizontal wind, and vertical wind should be related in a manner consistent with the AGW theory. An analysis of a subset of the WATS (vertical and horizontal wind and temperature) and NACS data (number density and, hence, mass density) and pressure (as a derived quantity, from number density and temperature) was performed to investigate whether such perturbations could be clearly shown to be due to AGWs by comparing quantitatively the various simultaneous data sets with AGW theory. Seven examples of wave‐like events in the vertical wind were studied, together with the accompanying variations in mass density, pressure, temperature, and horizontal wind. The pressure (acoustic) component of the density variation was calculated and then subtracted from the total density variation, allowing the wave‐induced vertical displacement amplitude to be found. This was compared to the vertical wind amplitude, via a spectral analysis, to yield estimates of the possible AGW frequency. The observed variation in the ratio of O/N2 number densities during the course of the oscillations was found to be consistent with the calculated altitude displacements. Phase lags in the number density perturbations between different species also appeared consistent with the AGW theory. Horizontal velocity perturbations in phase with the pressure perturbations were also seen. It is concluded that the oscillations are consistent with acoustic–gravity waves, where the pressure perturbation is nonnegligible. Phase relationships between the various observables can define the direction of wave travel to within 90° of azimuth, relative to the direction of spacecraft motion. For the seven cases detailed here, the derived (intrinsic) wave frequencies are close to, but slightly less than, the estimated local Brunt–Vaisala frequency, while the vertical displacement amplitudes were typically around ±25 km. All of the wave events studied in this work were located at high latitudes, poleward of the nominal location of the auroral oval.

The paper presents a set of Fiber Optic Distributed Temperature Sensing (FODS) experiments to expand the existing microstructure approach for horizontal turbulent wind direction by adding measurements of turbulent vertical wind speed and direction, as well as turbulent sensible heat flux.We address the observational challenge to isolate and quantify the weaker vertical turbulent motions from the much stronger mean advective flow signals. In the first part of this study, we test the ability of a cylindrical shroud to reduce the horizontal wind speed while keeping the vertical wind speed unaltered. Shroud experiments were performed using two sonic anemometers and two pressure ports in an open experimental area over short grass, with one observing system located inside the cylindrical shroud, but without any fiber-optic (FO) cables. The flow statistics were compared across shroud configurations of different shapes, colors, rigidity, and porosity. The white insect screen shroud with the rigid structure and 0.6 m diameter was identified as the most promising setup in which the correlation of flow properties between shrouded and unshrouded systems is maximized, and the RMSE was significantly lower. The optimum shroud setup reduces the horizontal wind standard deviation by 35 %, has a coefficient of determination of 0.972 for vertical wind standard deviations, and a RMSE less than 0.018 ms-1 when comparing the shrouded to the unshrouded setup. Spectral analysis showed a fixed ratio of spectral energy reduction in the low frequencies, e.g., > 2 s, for temperature and wind components, momentum, and sensible heat flux. Unlike low frequencies, the ratios decrease exponentially in the high frequencies, which means the shroud dampens the high-frequency eddies with a time scale < 6 s, considering both spectra and cospectra together. In the second part, the optimum shroud configuration was installed around a heated fiber-optic cable with attached microstructures in a forest to validate our findings, but the analysis revealed a failure to isolate the magnitude and sign of the vertical wind perturbations from FODS. However, concurrent observations from an unshrouded part of the FODS sensor in the weak-wind subcanopy of the forest (12–17 m above ground level) yielded meaningful measurements of the vertical motions from coherent structures with distinct sweep and ejection phases. These signals allow for detecting the turbulent vertical airflow at least 60 % of the time, and 71 % when conditional sampling was applied. Comparison with vertical wind perturbations from sonic anemometry resulted in correlation coefficients of 0.35 and 0.36, which increased to 0.53 and 0.62 for conditional sampling. Evaluating the first direct sensible heat fluxes from FODS against those from the classic eddy covariance using sonic anemometry yielded an encouraging agreement in both magnitude and temporal variability for selected periods. This observational achievement is an important step toward developing a FODS-based flux sensor capable of resolving heat flux continuously across spatial and temporal scales.

<strong class="journal-contentHeaderColor">Abstract.</strong> The paper presents a set of fiber-optic distributed temperature sensing (FODS) experiments to expand the existing microstructure approach for horizontal turbulent wind direction by adding measurements of turbulent vertical component, as well as turbulent sensible heat flux. We address the observational challenge to isolate and quantify the weaker vertical turbulent motions from the much stronger mean advective horizontal flow signals. In the first part of this study, we test the ability of a cylindrical shroud to reduce the horizontal wind speed while keeping the vertical wind speed unaltered. A white shroud with a rigid support structure and 0.6 m diameter was identified as the most promising setup in which the correlation of flow properties between shrouded and reference systems is maximized. The optimum shroud setup reduces the horizontal wind standard deviation by 35 %, has a coefficient of determination of 0.972 for vertical wind standard deviations, and a RMSE of less than 0.018 ms<span class="inline-formula">^−1</span> when compared to the reference. Spectral analysis showed a fixed ratio of spectral energy reduction in the low frequencies, e.g., <span class="inline-formula"><i>&lt;</i>0.5</span> Hz, for temperature and wind components, momentum, and sensible heat flux. Unlike low frequencies, the ratios decrease exponentially in the high frequencies, which means the shroud dampens the high-frequency eddies with a timescale <span class="inline-formula"><i>&lt;</i>6</span> s, considering both spectra and cospectra together. In the second part, the optimum shroud configuration was installed around a heated fiber-optic cable with attached microstructures in a forest to validate our findings. While this setup failed to isolate the magnitude and sign of the vertical wind perturbations from FODS in the shrouded portion, concurrent observations from an unshrouded part of the FODS sensor in the weak-wind subcanopy of the forest (12–17 m above ground level) yielded physically meaningful measurements of the vertical motions associated with coherent structures. These organized turbulent motions have distinct sweep and ejection phases. These strong flow signals allow for detecting the turbulent vertical airflow at least 60 % of the time and 71 % when conditional sampling was applied. Comparison of the vertical wind perturbations against those from sonic anemometry yielded correlation coefficients of 0.35 and 0.36, which increased to 0.53 and 0.62 for conditional sampling. This setup enabled computation of eddy covariance-based direct sensible heat flux estimates solely from FODS, which are reported here as a methodological and computational novelty. Comparing them against those from eddy covariance using sonic anemometry yielded an encouraging agreement in both magnitude and temporal variability for selected periods.

Aiming at investigating the vertical wave number spectral features of three‐dimensional winds in the lower atmosphere as well as their latitudinal and seasonal variations, we analyzed 11 year (1998–2008) radiosonde data from 92 United States stations in the Northern Hemisphere. The spatiotemporal variation of the horizontal wind spectral amplitude agrees well with that of the inertial gravity wave energy, revealing that the observed horizontal wind spectra are mainly attributed to the inertial gravity waves. The horizontal wind spectral slope is systematically and climatologically less negative than the canonical value of −3. For the first time we found that the vertical wind spectrum is much shallower than the horizontal wind spectrum over a wide latitude region, with slopes varying in −1.1 to −0.2 (−0.6 to 0.1) in the troposphere (lower stratosphere). Besides the slopes, the height, latitudinal, and seasonal variations of the vertical wind spectral showed evident difference from those of the horizontal wind spectrum. These differences are due to the horizontal and vertical wind spectra that might be constituted mainly by low and high frequency waves, respectively. Both the horizontal wind and vertical wind spectra exhibit evident universal features, which are more prominent in the lower stratosphere than in the troposphere, where it is thought to be the main source region of gravity waves, implying that the dynamical processes in the wave propagation might be the main cause of the universal spectrum. The background wind was found to have significant impact on the horizontal wind spectrum but has only weak impact on the vertical wind spectrum.

Microphysical modeling of Titan’s detached haze layer in a 3D GCM

Mountain waves are often assumed to remain steady with respect to time, but measurements of their vertical wind velocity by radar are known to show a clear time dependence. Specifically, the vertical wind W obeys a power law, where the spectral density varies as ω−5/3 over at least three orders of magnitude, and ω is the frequency. Power laws in the frequency and wave‐number spectra of parameters such as horizontal wind have been widely studied, but the frequency spectrum of mountain waves remains, by comparison, poorly understood. It is found that errors arising from the VHF radar measurement technique are not sufficient to explain the power law, and a previous model invoking vortical modes or two‐dimensional turbulence does not, on its own, explain entirely the W data. However, even a surprisingly simple model, in which the mountain‐wave pattern drifts upwind or downwind in a random walk, gives a similar time dependence to the observed W data. The radar data are contrasted with other observations and models, where W time variations have been interpreted in terms of lee‐wave trains with non‐zero phase speed; the relationship to other systems showing time‐scale invariant ωβ behaviour, such as 1/f noise, is also discussed.

Wind disturbance could render thrust and power variation or even causing roll which is difficult to maintain a steady flight in gust especially when the horizontal or vertical wind is involved. In this paper, the horizontal wind and vertical wind are presented to study the influence of wind disturbance on aerodynamic characteristics of the quadrotor aircraft in hovering by experiments and numerical simulations. First, the simplified aerodynamic model with the wind disturbance was analyzed in detail. Also, the low‐speed wind tunnel tests were performed to obtain the thrust and power variation of the quadrotor aircraft with rotor spacing ratio s = 1.1‐1.8 in both horizontal and vertical winds of 0‐5 m/s with the rotational speed ranging from 1500 to 2300 rpm. Finally, the simulations are performed by utilizing the Computational Fluid Dynamics (CFD) software ANSYS to study the flow field distribution of quadrotor with the influence of the wind disturbance. The comparison between experimental results and simulation results shows that the quadrotor achieves better aerodynamic performance with larger thrust and smaller power consumption at rotor spacing ratio s = 1.8. Additionally, the quadrotor can effectively resist the horizontal wind disturbance, which will bring larger power loading for the quadrotor, especially at 2.5 m/s. However, the vortices near blade‐tip move upwards and deform with the influence of vertical wind, resulting in the reduction of thrust and aerodynamic performance of the quadrotor.

The influences of horizontal wind gradients on “apparent” and “true” spaced antenna wind estimators are examined within the scope of a linear wind model. It is found that apparent velocity estimators are highly sensitive to horizontal gradients in horizontal wind components. Systematic errors in true velocity estimates increase with the probing radar beam width. For a beam width of ∼6° and realistic values of horizontal wind gradients, systematic errors in true velocity estimates remain less than ∼4 m/s at mesospheric altitudes in the absence of gradients in the vertical wind component.

Based on the quality-controlled observational spectral width data of the Beijing Mesosphere–Stratosphere–Troposphere (MST) radar in the altitudinal range of 3–19.8 km from 2012 to 2014, this paper analyzes the relationship between the proportion of negative turbulent kinetic energy (N-TKE) and the horizontal wind speed/horizontal wind vertical shear domain, and gives the distributional characteristics of atmospheric turbulence parameters obtained by using different calculation models. Three calculation models of the spectral width method were used in this study—namely, the H model (Hocking, 1985), N-2D model (Nastrom, 1997) and D-H model (Dehghan and Hocking, 2011). The results showed that the proportion of N-TKE in the H model increases with the horizontal wind speed and/or the vertical shear of horizontal wind speed, up to 80 %. When the horizontal wind speed is greater than 40 m·s−1, the proportion of N-TKE in the H model is greater than 60 %, and thus the H model is not applicable. When the horizontal wind speed is greater than 20 m s−1, the proportion of N-TKE in the N-2D model and D-H model increases with the horizontal wind speed, independent of the vertical shear of the horizontal wind speed, and the maximum values are 2 % and 4 %, respectively. However, it is still necessary to consider the applicability of the N-2D model and D-H model in some weather processes with strong winds. The distributional characteristics with height of the turbulent kinetic energy dissipation rate 𝜀 and the vertical eddy diffusion coefficient Kz derived by the three models are consistent with previous studies. Still, there are differences in the values of turbulence parameters. Also, the range resolution of the radar has little effect on the differences in the range of turbulence parameters' values. The median values of 𝜀 in the H model, N-2D model and D-H model are 10−3.2–10−2.8 m2 s−3, 10−2.8–10−2.4 m2 s−3 and 10−3.0–10−2.5 m2 s−3, respectively. The median values of Kz in these three models are 100.18–100.67 m2 s−1, 100.57–100.90 m2 s−1 and 100.44–100.74 m2 s−1.

The study focused on utilizing, for the first time ever, the data of the Halo Photonics Streamline XR Doppler LiDAR (Snoopy), which is an active remote sensing instrument that since January 2023 has been operating at the National Facility of the Cyprus Atmospheric Remote-Sensing Observatory (CARO) located in Limassol, Cyprus. The data spanned two full years of observations, from February 2023 to January 2025, in order to analyze the average wind patterns over the city, with the aim of understanding the diurnal, as well as the monthly and seasonal variations in both the horizontal wind speed and direction. The research involved processing data collected at various times of the day and across different atmospheric heights to calculate the mean horizontal wind and to identify common or characteristic patterns in the behaviour of the wind across months or seasons. An important outcome of this procedure is that the behaviour of the wind of this region can be sufficiently described through its separation into two periods of six months: the warm one from May till October, and the cold one from November until the month of April. The study also highlights the influence that local topographical factors have on the observed wind patterns, as both the land and sea breezes present a diurnal cycle and constitute a key characteristic of the winds that affect the city.

Ever since their discovery by glider pilots, mountain waves (MWs) are a well known atmospheric process to affect aviation as they can significantly modulate the atmospheric flow field on relatively short scales (λh ≈ 20 km). The goal of this thesis is to study the impact of such a flow field on high-flying aircraft (i.e. flight level (FL) &gt; 20.000 ft = FL200). For that reason, two cases were studied exemplarily where MWs affected flying conditions of the High Altitude LOng Range Research Aircraft, HALO in different ways. In the first case stall warnings at FL 410 (12.5 km) occurred unexpectedly during a research flight of HALO over Italy on 12 January 2016. At the incident location, the stratosphere was characterized by large horizontal variations in the along-track wind speed and temperature. On this day, the general atmospheric circulation favored the excitation and vertical propagation of large-amplitude mountain waves at and above the Apennines, Italy. These mountain waves had achieved large vertical energy fluxes of 8 W m−2 and propagated without significant dissipation from the troposphere into the stratosphere. Strong turbulence was encountered by HALO at FL 430 (13.8 km) on 13 October 2016 above Iceland which constitutes the second case study. In this event the turbulence caused altitude changes of about 50m within about 15s of the research aircraft. Additionally, the automatic thrust control of HALO could not control the large gradients in the horizontal wind speed and, consequently, the pilot had to deactivate this system. On that day, MWs were excited and propagated vertically above Iceland. In the altitude region of the turbulence encounter the atmosphere was characterized by a pronounced negative vertical shear of the horizontal wind. Here, in situ observations together with simulations of the Eulerian semi-Lagrangian fluid solver (EULAG) suggest that HALO was flying through the center of a breaking MW field. First, the question whether aircraft speed is dominantly influenced by the temperature or the horizontal wind could be answered. Analysis of high-resolution in situ observations and recordings of HALO’s Quick Access Recorder (’blackbox’) suggests that it is the horizontal wind speed which dominantly impacts aircraft speed of high flying aircraft. Second, it was found that vertically propagating MWs can affect flight conditions of high-flying aircraft. While turbulence is a well-acknowledged hazard to aviation, the case studies reveal that non-breaking, vertically propagating mountain waves also pose a potential hazard by modulating the ambient along-track wind speed on scales for which the response time of the avionic system is too slow. This may lead on the one hand to a decrease of the aircraft speed towards the minimum needed stall speed or on the other hand to variations in the aircraft speed that cannot be controlled by the automatic thrust control. Furthermore, in situ observations are compared to European Centre for Medium- Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) forecasts and operational analyses. This comparison revealed that large-scale structures are predicted very well. However, on scales smaller than 5km observed amplitudes of all meteorological parameters are underestimated. Here, the application of the Graphical Turbulence Guidance Tool (GTG) proved to be valuable for predicting the correct magnitude and location of the maximum encountered turbulence above Iceland. However, the observed intermittency could not be reproduced and a tendency to overpredict turbulence was found.

Small wind turbines (SWT), representing a relatively new technology in the field of renewable energies, exhibit potential for a notable contribution to a sustainable urban energy supply accelerated by international climate agreements [1]. However, many uncertainties remain regarding site assessment, especially in the built environment. Wind conditions in areas below 30 m above ground, where small wind turbines are preferably installed, are affected by complex aerodynamic effects. Urban areas feature conditions often not considered by common CFD models and calculations. This paper focuses on the impact of low-rise flat roof buildings on the ambient wind flow. Contrary to other investigations on wind flow around complex obstacles relying on numerical fluid flow simulations or scaled wind tunnel experiments, the performed investigation relies on measurements over a flat-roofed building. The data acquired over a span of 7 months by several 3D-ultrasonic anemometers at the Lichtenegg test site (Lower Austria) was examined. In order to determine the impact of the building on ambient wind conditions, the horizontal and vertical wind velocity, turbulence intensity and direction scatter at several locations were compared to the uninfluenced inflow conditions. Moreover, in addition to the commonly calculated horizontal turbulence intensity, the vertical turbulence intensity was considered to gain a deeper understanding for the occurring aerodynamic effects. The measurement results indicate that some locations on or around the building are not suited for installing wind turbines, while others show increased wind potential compared to undisturbed wind stream. Based on findings obtained by the wind assessment, recommendations for ideal placing of small wind turbines on low-rise buildings are given.