Large variations in balloon ascent rate over Hawaii

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) > 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.

Prefrontal mountain waves frequently occur in the lee of the mountains of the Western Cape province in South Africa. On 22 July 2010, four weather balloon soundings were conducted in this area on the upwind (one) and lee sides (three) of the Hex River Mountains. The purpose of these soundings was to detect rotors that occurred below trapped lee mountain waves, which can pose a significant danger to general aviation aircraft. A portable sounding system was employed to obtain atmospheric data of wind, temperature, pressure and humidity at 1-s intervals. These values were used to determine a Scorer parameter profile and Froude number for the upwind side of the mountain, which indicated the possibility for trapped lee wave development. Lee side rotors were analyzed using the reversed flow, updraft and downdraft speeds, along-ridge horizontal vorticity, potential temperature, wind speed, wind direction and Richardson number as determined from the sounding data. The vertical extent and approximate position of updraft areas of the rotors could be determined using areas of vertical wind shear, Richardson numbers below 0.25 and positions of local maxima in along-ridge horizontal vorticity. Upwind flanks of rotors were analyzed using along-ridge horizontal vorticity maxima and updraft areas. The top of one rotor was penetrated by a balloon.

Conduit processes during the climactic phase of the Shinmoe-dake 2011 eruption (Japan): Insights into intermittent explosive activity and transition in eruption style of andesitic magma

Abstract. Wind lidars are widespread and important tools in atmospheric observations. An intrinsic part of lidar measurement error is due to atmospheric variability in the remote-sensing scan volume. This study describes and quantifies the distribution of measurement error due to turbulence in varying atmospheric stability. While the lidar error model is general, we demonstrate the approach using large ensembles of virtual WindCube V2 lidar performing a profiling Doppler-beam-swinging scan in quasi-stationary large-eddy simulations (LESs) of convective and stable boundary layers. Error trends vary with the stability regime, time averaging of results, and observation height. A systematic analysis of the observation error explains dominant mechanisms and supports the findings of the empirical results. Treating the error under a random variable framework allows for informed predictions about the effect of different configurations or conditions on lidar performance. Convective conditions are most prone to large errors (up to 1.5 m s−1 in 1 Hz wind speed in strong convection), driven by the large vertical velocity variances in convective conditions and the high elevation angle of the scanning beams (62∘). Range-gate weighting induces a negative bias into the horizontal wind speeds near the surface shear layer (−0.2 m s−1 in the stable test case). Errors in the horizontal wind speed and direction computed from the wind components are sensitive to the background wind speed but have negligible dependence on the relative orientation of the instrument. Especially during low winds and in the presence of large errors in the horizontal velocity estimates, the reported wind speed is subject to a systematic positive bias (up to 0.4 m s−1 in 1 Hz measurements in strong convection). Vector time-averaged measurements can improve the behavior of the error distributions (reducing the 10 min wind speed error standard deviation to <0.3 m s−1 and the bias to <0.1 m s−1 in strong convection) with a predictable effectiveness related to the number of decorrelated samples in the time window. Hybrid schemes weighting the 10 min scalar- and vector-averaged lidar measurements are shown to be effective at reducing the wind speed biases compared to cup measurements in most of the simulated conditions, with time averages longer than 10 min recommended for best use in some unstable conditions. The approach in decomposing the error mechanisms with the help of the LES flow field could be extended to more complex measurement scenarios and scans.

Magmatic degassing, lava dome extrusion, and explosions from Mount Cleveland volcano, Alaska, 2011–2015: Insight into the continuous nature of volcanic activity over multi-year timescales

A combination of rawinsonde balloon ascent rates, low-elevation aircraft, and ground-based tracer sampling measurements are presented. These data indicate that mountain-induced gravity waves have a significant impact on the transport of ice crystals produced by the release of liquid propane from high-altitude dispensers along the crest of the northern Sierra Nevada in California. Special rawinsonde launches were made just downwind of the main Sierra Nevada crest. Balloon ascent rates show a very well defined mountain lee wave present during most precipitation events. Strong descent to the lee of the Sierra will thus have a detrimental effect on the growth of particles generated on the crest. The tracer SF6 (sulfur hexaflouride) is used to simulate the transport and dispersion of propane-generated ice crystals. Sulfur hexaflouride was released from two propane dispenser sites as a proxy for seeded ice crystals. Aircraft measurements of SF6 indicated that at the normal flight altitudes of 2500 m ov...

Dual-Doppler radar is a relatively new technology in the wind energy community and thus not yet studied vastly. This paper aims to compare horizontal wind speed and direction data retrieved from dual-Doppler radar and profiling lidars within the American WAKE experimeNt (AWAKEN) to investigate the influence of measurement height, wind direction and speed on the comparison. The 10-min averaged data show a better agreement of the measurements for higher altitudes, especially at faster wind speeds. For the wind direction, two sectors of larger differences in the measurements were detected: around 270° transient winds occur with a higher frequency than in other sectors. To explain the different measurement values in the wind direction sector around 90°, further studies, e.g. on the influence of atmospheric stability, are necessary.

This paper describes the formulation and the application of the nonhydrostatic anelastic vorticity model (TVM). This model is constructed using a method involving two horizontal streamfunctions and two horizontal vorticity components. The evaluation of this formulation is performed by simulating various bidimensional hydrostatic and nonhydrostatic mountain wave cases. Results are compared with analytical solutions and in particular with those developed by Laprise and Peltier for nonlinear forcings. The anelastic formulation is also validated with respect to the highly nonlinear 1972 Boulder windstorm. TVM is shown to accurately reproduce these mountain wave test cases in both its incompressible and anelastic formulations. In the second part of this paper, the adequacy of the hydrostatic and anelastic assumptions in simulating thermally induced circulations is investigated and compared to previous works. For a moderate surface thermal forcing, typical geographical setups are used and show slight differences between hydrostatic and nonhydrostatic horizontal wind speeds. For vertical wind speeds, differences are shown to be much larger and more sensitive to changes in grid resolution. For more stringent thermal surface forcing, differences remain low for horizontal wind speeds but increase considerably for the vertical wind component. The comparison between anelastic and incompressible solutions for the same cases shows the adequacy of the incompressible assumption when circulations are forced by the surface and are characterized by a relatively shallow vertical extent. In such conditions, virtually no differences are observed between the two formulations.

A simple quantitative model has been developed which predicts that a parametric correlation between the isotopic composition of precipitation and precipitation intensity can exist as a consequence of the condensation process when certain conditions are met. These conditions include the following: (1) approximate constancy, from one sampling interval to the next, of the initial isotopic composition of the water vapor in precipitation‐producing air masses; (2) approximate constancy of the initial condensation temperature; (3) approximate constancy of the rate of vertical ascent of the precipitating air mass; and (4) approximate constancy of the ratio of condensed water to water vapor. Such conditions are probably rare in nature for the short collection intervals represented by existing samples. However, with the probable exception of condition 3, tropical oceanic islands may satisfy the preceding conditions on the month‐to‐month time scale for which precipitation samples have generally been collected for isotopic analysis. Precipitation samples from Wake and Johnston islands that plot on the meteoric water line were used to compare monthly δD values with corresponding precipitation intensity. In general, there appears to be a convergence of the data at high values of δD (low intensity) and a divergence at low values of δD (high intensity). Such behavior is predicted by the isotopeintensity model largely in terms of variation in the vertical rate of ascent. For Wake Island this divergence of the data appears to be bimodal in character. However, for Johnston Island, there is considerable scatter in the data. This scatter is roughly constrained by the envelope defined by two vertical ascent rates that approximately characterize the presumably bimodal Wake Island trends. Thus much of the scatter in the Johnston Island data may be explained by month‐to‐variability in vertical ascent rates. The data for these two islands suggest that a simple precipitation δD versus intensity correlation is unlikely for monthly sample intervals. However, the issue remains unresolved for longer time scales.

Forty four isolates of Phytophthora infestans recovered from diseased potato leaves at the Volcano district on the island of Hawaii from 1986 to 1987 were all A1 mating type and sensitive to metalaxyl. However, all of the 23 isolates obtained from diseased tomato and potato leaves from the same area from 1994 to 1995 were all of the A2 mating type and resistant to metalaxyl. The recent isolates displayed considerable variation in growth rate and ability to produce sporangia. Substantial variation in growth rate, ability to produce sporangia and response to metalaxyl was also observed among zoospore progeny of a recent isolate tested. The possible mechanisms for the recent appearance of A2 mating type and diversity in growth rate, sporangial production and response to metalaxyl among the new population on the island of Hawaii are discussed.

<strong class="journal-contentHeaderColor">Abstract.</strong> Wind lidars are widespread and important tools in atmospheric observations. An intrinsic part of lidar measurement error is due to atmospheric variability in the remote-sensing scan volume. This study describes and quantifies the distribution of measurement error due to turbulence in varying atmospheric stability. While the lidar error model is general, we demonstrate the approach using large ensembles of virtual WindCube V2 lidar performing a profiling Doppler-beam-swinging scan in quasi-stationary large-eddy simulations (LESs) of convective and stable boundary layers. Error trends vary with the stability regime, time averaging of results, and observation height. A systematic analysis of the observation error explains dominant mechanisms and supports the findings of the empirical results. Treating the error under a random variable framework allows for informed predictions about the effect of different configurations or conditions on lidar performance. Convective conditions are most prone to large errors (up to 1.5 <span class="inline-formula">m</span> <span class="inline-formula">s⁻¹</span> in 1 <span class="inline-formula">Hz</span> wind speed in strong convection), driven by the large vertical velocity variances in convective conditions and the high elevation angle of the scanning beams (62<span class="inline-formula">^∘</span>). Range-gate weighting induces a negative bias into the horizontal wind speeds near the surface shear layer (<span class="inline-formula">−0.2</span> <span class="inline-formula">m</span> <span class="inline-formula">s⁻¹</span> in the stable test case). Errors in the horizontal wind speed and direction computed from the wind components are sensitive to the background wind speed but have negligible dependence on the relative orientation of the instrument. Especially during low winds and in the presence of large errors in the horizontal velocity estimates, the reported wind speed is subject to a systematic positive bias (up to 0.4 <span class="inline-formula">m</span> <span class="inline-formula">s⁻¹</span> in 1 <span class="inline-formula">Hz</span> measurements in strong convection). Vector time-averaged measurements can improve the behavior of the error distributions (reducing the 10 min wind speed error standard deviation to <span class="inline-formula">&lt;0.3</span> <span class="inline-formula">m</span> <span class="inline-formula">s⁻¹</span> and the bias to <span class="inline-formula">&lt;0.1</span> <span class="inline-formula">m</span> <span class="inline-formula">s⁻¹</span> in strong convection) with a predictable effectiveness related to the number of decorrelated samples in the time window. Hybrid schemes weighting the 10 min scalar- and vector-averaged lidar measurements are shown to be effective at reducing the wind speed biases compared to cup measurements in most of the simulated conditions, with time averages longer than 10 min recommended for best use in some unstable conditions. The approach in decomposing the error mechanisms with the help of the LES flow field could be extended to more complex measurement scenarios and scans.

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.

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.

The use of nacelle-based lidar systems for power performance testing of wind turbines is promising. Here, the knowledge of uncertainties is crucial. Wind field reconstruction is necessary to estimate wind field characteristics such as horizontal wind speed and wind direction from line-of-sight wind speed measurements using a wind flow model. In this work, two types of uncertainties in this process are investigated and confirmed in simulation: the uncertainty caused by measurement errors and by modeling errors. Based on this first investigation, the modeling uncertainty is exceeding the measurement uncertainty.

Wind lidar are widespread and important tools in atmospheric observations. An intrinsic part of lidar measurement error is due to atmospheric variability in the remote sensing scan volume. This study describes and quantifies the distribution of measurement error due to turbulence in varying atmospheric stability. While the lidar error model is general, we demonstrate the approach using large ensembles of virtual WindcubeV2 lidar performing profiling doppler-beam-swinging (DBS) scans in quasi-stationary large-eddy simulations (LES) of convective and stable boundary layers. Error trends vary with the stability regime, time-averaging of results, and observation height. A systematic analysis of the observation error explains dominant mechanisms and supports the findings of the empirical results. Treating the error under a random variable framework allows for informed predictions about the effect of different configurations or conditions on lidar performance. Convective conditions are most prone to large errors, driven by the large vertical velocities in convective plumes and exacerbated by the high elevation angle of the scanning beams. The violations of the assumption of horizontal homogeneity due to filtered turbulent velocity variances dominate the error variance, with the vertical velocity variations of particular importance. Range gate weighting contributes little to the variability of the error, but induces an underestimating bias into the horizontal velocity near the surface shear layer. Error in the horizontal wind speed and direction computed from wind components is sensitive to the background wind speed but has negligible dependence on the relative orientation of the instrument. Especially during low winds and in the presence of large errors in the u and v velocity estimates, the reported wind speed is subject to a systematic positive bias. Vector time-averaged measurements can improve the behavior of the error distribution with a predictable effectiveness related to the number of decorrelated samples in the time window. The approach in decomposing the error mechanisms with the help of the LES flow field extends to more complex measurement scenarios and scans.