Improved Wind Measurements on Research Aircraft

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.

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.

Two networks of meteorological stations are used to investigate the spatial variability of temperature, wind speed, turbulent kinetic energy, turbulent fluxes and turbulent spectra over horizontal distances of tens to hundreds of metres . The networks are located in regions of moderately complex terrain, with stations located at elevation differences as large as 37 m at Pedras Altas and 10 m at Santa Maria. The spatial temperature variability is largely enhanced on very stable, weak-wind nights. At Pedras Altas, the temperature difference reaches 12 K between stations horizontally separated by less than 500 m. Obstacles also play an important role, as obstructed sites may have temperatures a few K lower than unobstructed sites at the same elevation. The maximum wind speed over the network (Vmax) controls the horizontal variability of mean and turbulent quantities. Despite the terrain and horizontal scale differences, variables such as mean temperature, standard deviations of horizontal and vertical wind components and the turbulent fluxes of sensible heat, latent heat and carbon dioxide share the dependence on Vmax at both sites. The regime transition between the very stable and weakly-stable boundary layers occurs at much lower wind speeds at an obstructed site than at a hilltop.

Precise knowledge of winds and temperatures in the middle atmosphere is critical for the localization and characterization of infrasound sources. We present the concept, design, and measurement capabilities of a compact, mobile Doppler lidar system developed at the Leibniz Institute of Atmospheric Physics (IAP). This system, is designed for Doppler-Mie, -Rayleigh, and -resonance measurements in the middle atmosphere.The daylight-capable instrument features a compact volume of about 1 m³ and is engineered for easy deployment as part of an array of lidar units. We highlight recent results, emphasizing collocated, high-resolution measurements of wind and temperature. By employing three to five individual fields of view, the system can measure both horizontal and vertical wind components. Between altitudes of 3 and 25 km, the instrument utilizes the narrowband properties of Mie backscatter, relying solely on aerosol backscatter to achieve precise three-dimensional wind measurements. In this altitude range, a novel method enables the measurement of vertical winds with an accuracy better than 0.5 m/s and a time resolution of just 60 seconds.Above 25 km, winds will be measured using Doppler-Rayleigh and -resonance techniques. Concurrent Rayleigh temperature measurements utilize advanced aerosol correction methods, taking advantage of the instrument's high sensitivity to aerosols.The feasibility of integrating this lidar system into a European lidar array is being investigated within the EULIAA (European Lidar Array for Atmospheric Climate Monitoring) project. The transfer of this technology to industry is currently being developed through the LidarCUBE project.

Mean and Turbulence Statistics in a Wintertime Convectively-mixed Boundary Layer Over Lake Michigan

A two-dimensional, nonhydrostatic, coupled, earth/atrnospheric model has been used to simulate mean and turbulent atmospheric characteristics near lines of extreme surface heating. Prognostic equations are used to solve for the horizontal and vertical wind components, potential temperature,and turbulent kinetic energy (TKE). The model computes nonhydrostatic pressure deviations from a derived atmospheric continuity equation. Hori- zontal pressure gradients generated from surface heating are calculated from thermal wind principles. Model simulations indicate the development of buoyancy-induced horizontal roll vortices near regions with surface temperatures typical of wildland fires. Model results are qualitatively similar to previous wind-tunnel experiments. When surface temperatures are increased, the circulations associated with the roll vortices become more vigorous. The introduction of a weak ambient flow in a direction perpendicular to the line of heating has a major influence on the simulated circulation patterns aid nonhydrostatic pressure deviations near the line of heating. The effect is more pronounced for lower surface temperatures at the heating line. The TKE profiles reveal preferred regions of TKE growth that can be attributed mainly to buoyancy or advection effects.

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.

The vertical profiles of the wind speed and direction in atmospheric boundary layers are strongly controlled by turbulence. Most global weather forecast and climate models parameterize the vertical transport of horizontal momentum by turbulent eddies by means of a downgradient eddy diffusion approach, in which the same stability‐dependent eddy viscosity profile is applied to both horizontal wind components. In this study we diagnose eddy viscosity profiles from large‐eddy simulations of five convective boundary layers with wind shear. Each simulation was forced by the same geostrophic wind of 7.5 , but with different surface heat fluxes in the range between 0.03 and 0.18 . We find that the eddy viscosity profiles for the two horizontal wind components differ significantly, in particular, we diagnose negative eddy viscosities, indicating vertical turbulent transport that is counter the mean gradient. This suggests that a purely downgradient diffusion approach for turbulent momentum fluxes is inadequate. A modified solution of the Ekman spiral demonstrates that different eddy viscosity profiles for the two horizontal wind components lead to a different wind profile. To improve parameterizations that apply a downgradient diffusion approach for momentum, correction terms to allow for non‐local, boundary‐layer scale transport should be incorporated.

Seven years of ozone and total nitrate (the sum of gaseous HNO3 and particulate NO3−) data are analyzed to quantify the seasonal cycles of ozone production and transport in the boundary layer at 60°N over the Baltic Sea. This analysis is based on the statistical correlations between ozone and total nitrate and the covariances between trace species and wind components. Ozone production efficiencies are highest near the summer solstice, decreasing to low values in March, April, and October. In winter, precursor emissions effectively deplete ozone. Horizontal average and transient fluxes of ozone and total nitrate in the boundary layer were estimated as the covariances between trace gas concentrations and horizontal wind components. A year‐round northward flux of total nitrate, 2.0 μg(N) m−2 s−1 as annual average, was observed. This is the sum of a northeastward flux by the average wind field and a northwestward flux by synoptic‐scale transient eddies. Embedded in an east‐northeastward flux of background ozone, the sums of the components of the transient and estimated average flux divergence over Europe show large northward fluxes in summer and southward fluxes in winter. In summer, these fluxes are due to photochemically produced elevated ozone concentrations. In winter, high winds advect background ozone into the European continent which then acts as a sink area. The average effect of European precursor emissions on the horizontal flux was estimated assuming that it is the sum of the transient eddy component and the estimated average upwind divergence component over Europe. The northward component of these fluxes is higher in summer, with a highest monthly average in July of 49 μg m−2s−1, compared to the southward fluxes in winter, with a highest value of 44 μg m−2 s−1 in December, resulting in a northward yearly average flux of 6 μg m−2 s−1. The sum of the transient eddy flux component and the estimated average divergence flux component over Europe is estimated to affect monthly horizontal total ozone fluxes by 32–68% in the period April‐September, but only by 3–23% during the winter months.

To evaluate the effect of wind on corona discharges occurring on the tip of a grounded rod during a negative charging process of thundercloud, a two‐dimensional numerical model has been improved by considering the wind velocity as a driving force for the movement of the corona charges. It was found that not only wind speed but also wind direction have a significant effect on the distribution of corona charges, the local electric field around the rod, and the corona current. (1) Under the same wind speed, a larger horizontal wind can result in less accumulation of corona charges, a larger electric field, and a larger corona current. However, when the speed is less than 5 m s−1, the effect of wind direction on the corona current was weak. (2) Under the same wind direction, a larger wind speed can cause a larger corona current. However, when the horizontal wind component is smaller than the vertical, the larger wind speed would cause a smaller electric field. Thus, it is necessary to take the effects of the wind direction into consideration, rather than to consider its speed only, when studying the corona discharge and its effects on the upward leader.

When the wind speed decreases below a certain value (1–2 m s-1) meandering (low frequency horizontal wind oscillations) starts to prevail. In these conditions it becomes difficult to define a precise mean wind direction and to estimate the airborne dispersion. To study the wind and turbulence characteristics during meandering, two sonic anemometer datasets, containing hourly wind observations, were analysed: the first one, lasting 1 year, was recorded in complex terrain (Graz, Austria) and the second one, lasting about 1month, was recorded in a rather flat area (Tisby, Sweden). It was found that meandering seems to exist under all meteorological conditions regardless of the stability or wind speed and it was confirmed that meandering sets a lower limit for the horizontal wind component variances. Further, it was found that the autocorrelation functions of the horizontal wind components, computed for the low wind cases, show an oscillating behaviour with the presence of large negative lobes. Two different relationships from the literature, and relevant to these oscillatory aspects, were fitted to the data. They contain two parameters: one associated and relevant to the classical integral time scale and the second with meandering occurrence. Based on these relationships, expressions for the mean square displacement of particles σy2(t) were also derived.

Aircraft Control System Using LQG and LQR Controller with Optimal Estimation-Kalman Filter Design

Generalizing radar interferometry to three‐dimensional space, we present a model which predicts the variation with respect to frequency of the phase of the cross‐spectrum obtained between two separate antennas. The slope of this variation is proportional to the cosine of the angle between the horizontal wind and the interferometer baseline, and inversely proportional to the horizontal wind amplitude. The zero‐frequency phase depends on the horizontal wind speed and direction, on the vertical wind velocity, and on the anisotropy of the backscattered power with respect to the zenith. The model also allows us to predict qualitatively the effects of specularity, beam shape, and random turbulence on the phase versus frequency variation. Assuming a spaced receiver setup with three baselines rotated by 120°, we present an implementation scheme of the radar interferometry technique which yields a three‐dimensional wind estimate and a parameter characterizing the anisotropy of the echo power distribution. Finally, we argue that the radar interferometry horizontal wind measurements will suffer from limitations similar to those of the so‐called apparent velocity as both techniques are related by Fourier transform, and that the vertical wind component will be unbiaised by anisotropy in the backscattered power.

We have successfully designed, developed, and tested the blades, a wind lens, and a wind deflection ramp. The lens and ramp were capable of increasing the output power of the wind turbine. Since the power output of an ideal wind turbine is a function of wind speed cubed, these modifications were designed to increase the velocity of the wind before it reached the blades. The lens creates a low-pressure region at the exit area of the lens, which generates vortices and draws the wind through the blades at a higher velocity. The wind deflection ramp, which was designed to operate at a wind speed of 7 m/s, increased the power output by directing more wind into the turbines blades. The test data was compared to theoretical calculations to evaluate the results. All of the design and testing methodology as well as theoretical and experimental results are explained throughout the body of this paper.

The coplane analysis technique for mapping the three-dimensional wind field of precipitating systems is applied to the NASA High-Altitude Wind and Rain Airborne Profiler (HIWRAP). HIWRAP is a dual-frequency Doppler radar system with two downward-pointing and conically scanning beams. The coplane technique interpolates radar measurements onto a natural coordinate frame, directly solves for two wind components, and integrates the mass continuity equation to retrieve the unobserved third wind component. This technique is tested using a model simulation of a hurricane and compared with a global optimization retrieval. The coplane method produced lower errors for the cross-track and vertical wind components, while the global optimization method produced lower errors for the along-track wind component. Cross-track and vertical wind errors were dependent upon the accuracy of the estimated boundary condition winds near the surface and at nadir, which were derived by making certain assumptions about the vertical velocity field. The coplane technique was then applied successfully to HIWRAP observations of Hurricane Ingrid (2013). Unlike the global optimization method, the coplane analysis allows for a transparent connection between the radar observations and specific analysis results. With this ability, small-scale features can be analyzed more adequately and erroneous radar measurements can be identified more easily.