Mountain-Wave Turbulence Encounter of the Research Aircraft HALO above Iceland

AbstractStrong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO) at flight level 430 (13.8 km) on 13 October 2016 above Iceland. In this event the turbulence caused altitude changes of the research aircraft of about 50 m within a period of approximately 15 s. Additionally, the automatic thrust control of the HALO could not control the large gradients in the horizontal wind speed and, consequently, the pilot had to switch off this system. Simultaneously, the French Falcon of Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE), flying 2 km below HALO, also encountered turbulence at almost the same location. On that day, mountain-wave (MW) excitation and propagation was favored by the alignment of strong surface winds and the polar front jet. We use a combination of in situ observations, ECMWF and empirical turbulence forecasts, and high-resolution simulations to characterize the observed turbulent event. These show that a pronounced negative vertical shear of the horizontal wind favored overturning and breaking of MWs in the area of the encountered turbulence. The turbulent region was tilted upstream and extended over a distance of about 2 km in the vertical. The analyses suggest that HALO was flying through the center of a breaking MW field while the French Falcon encountered the lower edge of this region. Surprisingly, the pronounced gradients in the horizontal wind speeds leading to the deactivation of the automatic thrust control were located north of the breaking MW field. In this area, our analysis suggests the presence of gravity waves that could have generated the encountered modulation of the horizontal wind field.

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Wind Field Characterization from the Trajectories of Small Balloons

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-11-00081.1 ◽

2012 ◽

Vol 29 (9) ◽

pp. 1236-1249 ◽

Cited By ~ 4

Author(s):

Thomas D. Wilkerson ◽

Alan B. Marchant ◽

Thomas J. Apedaile

Keyword(s):

High Spatial Resolution ◽

Aerodynamic Drag ◽

Vertical Shear ◽

Horizontal Wind ◽

Aerosol Transport ◽

Wind Fields ◽

Horizontal Wind Speed ◽

Wind Speeds ◽

Sensing System

Abstract This paper reports the development and application of a new wind sensing system, ValidWind. ValidWind consists of small, helium-filled tracer balloons and an instrument that tracks them with high spatial resolution by means of an eye-safe lidar rangefinder and records 3D balloon position as a function of time. Lightweight retroreflectors attached to the balloons enhance the optical range. Balloon tracking is automatic. The data products include horizontal wind speed, wind direction, and vertical shear as functions of time and geolocation. Vertical wind speeds can be inferred from variations of the balloons’ rate of rise given the balance between buoyancy and aerodynamic drag. Applications of ValidWind include characterization of katabatic and ridge-top wind fields and monitoring of windborne aerosol transport. The capability of ValidWind balloons to provide useful profiles of the wind from the ground up to an altitude of 2 km AGL is presented and analyzed.

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Snow Transport Over Mountain Crests

Journal of Glaciology ◽

10.1017/s0022143000010984 ◽

1980 ◽

Vol 26 (94) ◽

pp. 469-480 ◽

Cited By ~ 37

Author(s):

Paul M. B. Föhn

Keyword(s):

Quantitative Relationship ◽

Horizontal Wind ◽

Snow Surface ◽

Horizontal Wind Speed ◽

Ridge Crest ◽

Wind Speeds ◽

Drift Flux ◽

Strong Winds ◽

Wind Profiles ◽

Snow Transport

AbstractIn order to gain more insight into the mountain snow-transport mechanisms wind and drift flux measurements have been executed on a ridge crest (mainly during snow-storms). Horizontal wind-speed profiles, measured between 0.3 and 6 m above snow surface, show a hump-shaped course especially for strong winds. Theoretical approximations substantiate that the Bernoullian pressure decrease on the crest may be the main cause for this type of wind profile. Roughness parameters (Z0, u⋆) are determined with the aid of the wind profiles and compared with those reported in the literature. Corresponding drift density profiles coincide with steady-state drift theories as long as wind speeds are low (u1≤ 7-10 m s-1), at greater wind speeds snow plumes of 1 to 1.5 m thickness develop immediately above snow surface. Areal measurements on snow mass-balance differences between windward and lee slopes are used to approximate the total transport over the ridge crest and to derive a quantitative relationship between crest winds and drift-snow deposition on lee slopes.

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Wind sensing with drone-mounted wind lidars: proof of concept

Atmospheric Measurement Techniques ◽

10.5194/amt-13-521-2020 ◽

2020 ◽

Vol 13 (2) ◽

pp. 521-536

Author(s):

Nikola Vasiljević ◽

Michael Harris ◽

Anders Tegtmeier Pedersen ◽

Gunhild Rolighed Thorsen ◽

Mark Pitter ◽

...

Keyword(s):

Wind Speed ◽

Continuous Wave ◽

Position Control ◽

Horizontal Wind ◽

Lidar Measurement ◽

Proof Of Concept ◽

Horizontal Wind Speed ◽

Wind Speeds ◽

Potential Applications ◽

Wind Measurements

Abstract. The fusion of drone and wind lidar technology introduces the exciting possibility of performing high-quality wind measurements virtually anywhere. We present a proof-of-concept (POC) drone–lidar system and report results from several test campaigns that demonstrate its ability to measure accurate wind speeds. The POC system is based on a dual-telescope continuous-wave (CW) lidar, with drone-borne telescopes and ground-based optoelectronics. Commercially available drone and gimbal units are employed. The demonstration campaigns started with a series of comparisons of the wind speed measurements acquired by the POC system to simultaneous measurements performed by nearby mast-based sensors. On average, an agreement down to about 0.1 m s−1 between mast- and drone-based measurements of the horizontal wind speed is found. Subsequently, the extent of the flow disturbance caused by the drone downwash was investigated. These tests vindicated the somewhat conservative choice of lidar measurement ranges made for the initial wind speed comparisons. Overall, the excellent results obtained without any drone motion correction and with fairly primitive drone position control indicate the potential of drone–lidar systems in terms of accuracy and applications. The next steps in the development are outlined and several potential applications are discussed.

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Effects of Fences and Green Zones on the Air Flow and PM2.5 Concentration around a School in a Building-Congested District

Applied Sciences ◽

10.3390/app11199216 ◽

2021 ◽

Vol 11 (19) ◽

pp. 9216

Author(s):

Soo-Jin Park ◽

Geon Kang ◽

Wonsik Choi ◽

Do-Yong Kim ◽

Jinsoo Kim ◽

...

Keyword(s):

Horizontal Wind ◽

Convergence Region ◽

Statistical Validation ◽

Horizontal Wind Speed ◽

The Road ◽

Wind Speeds ◽

Flow Convergence ◽

Computational Fluid Dynamics Cfd ◽

Tree Type ◽

Pm2.5 Concentration

We investigated the effects of wall- and tree-type fences on the airflow and fine particular matter (PM2.5) concentration around a school using a computational fluid dynamics (CFD) model. First, we validated the simulated wind speeds and PM2.5 concentrations against measured values, and the results satisfied the recommended criteria of the statistical validation indices used. Then, we evaluated the fence effects for 16 inflow directions by conducting numerical simulations with different fence types and heights. With east–southeasterly inflow, relatively high PM2.5 from the road was transported to the school. However, the wall-type fence prevented the PM2.5 from the road from entering the school, and the PM2.5 concentration decreased significantly downwind of the fence. With east–northeasterly inflow, the horizontal wind speed decreased due to the drag caused by the tree-type fence, resulting in a shift in the flow convergence region. The PM2.5 concentration decreased in the region of strengthened upward flow. This occurred because the number of pollutants transported from the background decreased. A comparison of the two fence types revealed that the effect of the tree-type fence on inbound pollutants was more significant, due to increased upward flows, than the effect of the wall-type fence.

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Turbulence parameters measured by the Beijing Mesosphere–Stratosphere–Troposphere radar in the troposphere/lower stratosphere with three models: Comparison and analyses

10.5194/amt-2021-309 ◽

2022 ◽

Author(s):

Ze Chen ◽

Yufang Tian ◽

Yinan Wang ◽

Yongheng Bi ◽

Xue Wu ◽

...

Keyword(s):

Wind Speed ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Spectral Width ◽

Vertical Shear ◽

Horizontal Wind ◽

Horizontal Wind Speed ◽

Turbulence Parameters ◽

2D Model ◽

Calculation Models

Abstract. 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.

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Snow Transport Over Mountain Crests

Journal of Glaciology ◽

10.3189/s0022143000010984 ◽

1980 ◽

Vol 26 (94) ◽

pp. 469-480 ◽

Cited By ~ 5

Author(s):

Paul M. B. Föhn

Keyword(s):

Quantitative Relationship ◽

Horizontal Wind ◽

Snow Surface ◽

Horizontal Wind Speed ◽

Ridge Crest ◽

Wind Speeds ◽

Drift Flux ◽

Strong Winds ◽

Wind Profiles ◽

Snow Transport

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Wind measurements using a LIDAR on a buoy

RBRH ◽

10.1590/2318-0331.252020200053 ◽

2020 ◽

Vol 25 ◽

Author(s):

Felipe Barros Nassif ◽

Felipe Mendonça Pimenta ◽

Arcilan Trevenzoli Assireu ◽

Carla de Abreu D’Aquino ◽

Julio César Passos

Keyword(s):

Mechanical System ◽

Inertial Sensor ◽

Resource Assessment ◽

Horizontal Wind ◽

Aquatic Environments ◽

Mobile Platforms ◽

Horizontal Wind Speed ◽

Promising Alternative ◽

Wind Speeds ◽

Wind Measurements

ABSTRACT LIDAR technology is a promising alternative for the measurement of winds, requiring less maintenance and lower costs than meteorological towers. They are capable of remotely profiling winds by means of an infrared laser, which is backscattered by aerosols and particles carried by the air. The LIDAR can be assembled on fixed or mobile platforms. When installed on platforms such as moored buoys, the motion caused by waves must be evaluated and corrected. This study describes the use of a mechanical system and analytical methods for the motion compensation of a buoy-mounted LIDAR. A 24-hour experiment was conducted on Furnas Hydroelectric Reservoir to test the mechanical system, evaluate residual motions, and assess the winds. Correction algorithms for the horizontal wind speeds were applied using pitch and roll measurements, provided by an inertial sensor. Analyses demonstrate that horizontal wind speed errors are negligible for buoy inclinations of less than 20 degrees. The buoy-mounted LIDAR represents an economical solution for wind profiling and resource assessment of aquatic environments.

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Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower

Atmosphere ◽

10.3390/atmos11111210 ◽

2020 ◽

Vol 11 (11) ◽

pp. 1210

Author(s):

Hiroki Okachi ◽

Tomohito J. Yamada ◽

Yasuyuki Baba ◽

Teruhiro Kubo

Keyword(s):

Wind Speed ◽

Size Distribution ◽

Drop Size ◽

State Of The Art ◽

Drop Size Distribution ◽

Open Ocean ◽

Horizontal Wind ◽

Sea Spray ◽

Horizontal Wind Speed ◽

Wind Speeds

The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter μ of the Ulbrich distribution decreased. This decreasing trend can be recognized as an increase in sea spray. During no-rainfall hours (indicated by rain gauges on the ocean tower and nearby land), sea spray DSDs were obtained at various horizontal wind speeds. Furthermore, the proportions of sea spray to rainfall at different rainfall intensities and horizontal wind speeds were determined; at a horizontal wind speed of 16 to 20 m s−1, the average sea spray proportions were 82.7%, 19.1%, and 5.3% during total rainfall periods of 2.1 mm h−1, 8.9 mm h−1, and 32.1 mm h−1, respectively. Representation of sea spray DSDs, as well as rainfall DSDs, is a key element of calculating real rainfall intensities over the open ocean.

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An Extreme Event in the Eyewall of Hurricane Felix on 2 September 2007

Monthly Weather Review ◽

10.1175/mwr-d-16-0364.1 ◽

2017 ◽

Vol 145 (6) ◽

pp. 2083-2092 ◽

Cited By ~ 10

Author(s):

Sim D. Aberson ◽

Jun A. Zhang ◽

Kelly Nuñez Ocasio

Keyword(s):

Extreme Event ◽

Intensity Change ◽

Horizontal Wind ◽

Small Scale ◽

Data Systems ◽

Mixing Processes ◽

Wind Speeds ◽

Flight Level ◽

Hurricane Isabel ◽

New Evidence

Abstract During a routine penetration into Hurricane Felix late on 2 September 2007, NOAA42 encountered extreme turbulence and graupel, flight-level horizontal wind gusts of over 83 m s−1, and vertical wind speeds varying from 10 m s−1 downward to 31 m s−1 upward and back to nearly 7 m s−1 downward within 1 min. This led the plane to rise nearly 300 m and then return to its original level within that time. Though a dropwindsonde was released during this event, the radars and data systems on board the aircraft were rendered inoperable, limiting the amount of data obtained. The feature observed during the flight is shown to be similar to that encountered during flights into Hurricanes Hugo (1989) and Patricia (2015), and by a dropwindsonde released into a misovortex in Hurricane Isabel (2003). This paper describes a unique dataset of a small-scale feature that appears to be prevalent in very intense tropical cyclones, providing new evidence for eye–eyewall mixing processes that may be related to intensity change.

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On strongly nonlinear gravity waves in a vertically sheared atmosphere

Mathematics of Climate and Weather Forecasting ◽

10.1515/mcwf-2020-0103 ◽

2020 ◽

Vol 6 (1) ◽

pp. 63-74

Author(s):

Mark Schlutow ◽

Georg S. Voelker

Keyword(s):

Gravity Waves ◽

Lower Layer ◽

Vertical Shear ◽

Horizontal Wind ◽

Necessary Condition ◽

Mean Flow ◽

Individual Layer ◽

Strongly Nonlinear ◽

The Mean ◽

The Stability

Abstract We investigate strongly nonlinear stationary gravity waves which experience refraction due to a thin vertical shear layer of horizontal background wind. The velocity amplitude of the waves is of the same order of magnitude as the background flow and hence the self-induced mean flow alters the modulation properties to leading order. In this theoretical study, we show that the stability of such a refracted wave depends on the classical modulation stability criterion for each individual layer, above and below the shearing. Additionally, the stability is conditioned by novel instability criteria providing bounds on the mean-flow horizontal wind and the amplitude of the wave. A necessary condition for instability is that the mean-flow horizontal wind in the upper layer is stronger than the wind in the lower layer.

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