Dual‐Doppler lidar observation of horizontal convective rolls and near‐surface streaks

Iwai, Hironori; Ishii, Shoken; Tsunematsu, Nobumitsu; Mizutani, K.; Murayama, Yasuhiro; Itabe, Toshikazu; Yamada, Izumi; Matayoshi, Naoki; Matsushima, Dai; Sha, Wei E. I.; Yamazaki, Takeshi; Iwasaki, Toshiki

doi:10.1029/2008gl034571

Cited by 27 publications

(42 citation statements)

References 18 publications

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“…The idea is that a properly configured initial perturbation can grow to counter-rotating vortices that are tilted into the mean shear. Kim and Park (2003) and Iwai (2008), for example, mentioned a relationship between low-speed streak formation and the development of large-scale horizontal rolls. Both, the mixed-layer rolls and the streaks, can be linked to microfronts, which can be observed in sweep-and-ejection patterns or ramp-like patterns in the time series of wind velocity, temperature, and humidity (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…They have a much smaller extent compared to mixed-layer rolls with only 100-200 m vertical extent and 500-2,000 m in the streamwise direction (e.g. Moeng and Sullivan 1994;Kim and Park 2003;Newsom et al 2008;Iwai 2008). Drobinski and Foster (2003) referred the lifetimes of the streaks to several tens of min.…”

Section: Introductionmentioning

confidence: 99%

“…They used two lidars to span a triangular area of approximately 3 km 2 and a scan technique that allowed horizontal windfield reproduction with a temporal resolution of 30 s. They demonstrated the qualitative behaviour of the streamwise and the cross-stream wind components during two situations with unstable, one with neutral and one with weakly stable conditions and estimated the corresponding length scales. Dual Doppler lidar was also used by Iwai (2008) to demonstrate the interaction between convective rolls and near-surface streaks. Both studies demonstrated that dual Doppler lidar is highly promising for coherent structure research, particularly for streaky structures.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Träumner

Damian

Stawiarski

et al. 2014

Boundary-Layer Meteorol

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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 m s −1 . During neutral to stable situations, the eddies were on average quite isotropic in the horizontal plane.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Turbulent Structures and Coherence in the Atmospheric Surface Layer

Träumner

Damian

Stawiarski

et al. 2014

Boundary-Layer Meteorol

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“…Dual-Doppler lidar methods seem to provide a valuable supplement here, since they allow the measurement of the complete two-dimensional wind field with a spatial resolution of a few tens of metres and a time resolution of the order of 10 s on planes of several km 2 in size. It has been shown that surface-layer streaks can be detected with horizontal dual-Doppler lidar scans (Newsom et al 2008;Iwai et al 2008) and a recent study by Träumner et al (2014) derived their length scales depending on stability and background wind speed. However, the limited time and spatial resolutions due to scan duration and the extent of the lidar pulse lead to severe inherent averaging in the resulting wind fields (Stawiarski et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Assessment of Surface-Layer Coherent Structure Detection in Dual-Doppler Lidar Data Based on Virtual Measurements

Stawiarski

Träumner

Kottmeier

et al. 2015

Boundary-Layer Meteorol

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Dual-Doppler lidar has become a useful tool to investigate the wind-field structure in two-dimensional planes. However, lidar pulse width and scan duration entail significant and complex averaging in the resulting retrieved wind-field components. The effects of these processes on the wind-field structure remain difficult to investigate with in situ measurements. Based on high resolution large-eddy simulation (LES) data for the surface layer, we performed virtual dual-Doppler lidar measurements and two-dimensional data retrievals. Applying common techniques (integral length scale computation, wavelet analysis, twodimensional clustering of low-speed streaks) to detect and quantify the length scales of the occurring coherent structures in both the LES and the virtual lidar wind fields, we found that, (i) dual-Doppler lidar measurements overestimate the correlation length due to inherent averaging processes, (ii) the wavelet analysis of lidar data produces reliable results, provided the length scales exceed a lower threshold as a function of the lidar resolution, and (iii) the low-speed streak clusters are too small to be detected directly by the dual-Doppler lidar. Furthermore, we developed and tested a method to correct the integral scale overestimation that, in addition to the dual-Doppler lidar, only requires high-resolution wind-speed variance measurements, e.g. at a tower or energy balance station.

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“…Clark et al (1994) described the fine-scale structure of gusts using lidar and simulated windstorms using two-and three-dimensional models to examine impacts of three-dimensionality, surface friction, and horizontal resolution on windstorms. We have also studied the feasibility of a mobile Doppler lidar that was developed at the National Institute of Information and Communication Technology (NICT) for observing local circulation (Ishii et al 2007(Ishii et al , 2008Sasaki et al 2010). In this work, intensive observations were conducted to target the strong downslope winds of the Zao mountain range during the winter monsoon season with a lidar system that was installed at the western corner of Sendai Airport.…”

Section: Introductionmentioning

confidence: 99%

Transient Downslope Winds under the Influence of Stationary Lee Waves from the Zao Mountain Range

Sawada

Iwasaki

Sha

et al. 2012

Journal of the Meteorological Society of Japan

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Severe downslope winds accompanying turbulence, which are of great concern to aviation safety, often occur on the lee side of Zao mountain range in winter. Special Doppler lidar observations and numerical simulations with a grid spacing of 100 m were carried out focusing on the downslope winds around the Sendai airport on 14 February 2008. The model reproduced stationary lee waves with an approximate 20-km wavelength, consistent with the observed horizontal scale in water vapor images from the Japanese geostationary multifunctional transport satellite (MTSAT-1R). The simulated lee waves are accompanied by strong vertical shear, which leads to the separation of a vortex sheet from the surface, where small-scale vortices are generated successively. The vortex sheet is under favorable conditions for Kelvin-Helmholtz instability and may account for the generation of small-scale vortices. The simulated vortices, which are advected downstream, are accompanied by weak low-level wind patches. The Doppler lidar observation also captured the weak low-level wind patches with a horizontal scale of 1000-m moving downstream near the surface. An observed temporal variability in line-of-site wind speed decreased with increasing altitude from the surface. This feature was reproduced by the model in a qualitative sense, although the model tended to overestimate (underestimate) the variability below (above) a height of approximately 800 m.

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Dual‐Doppler lidar observation of horizontal convective rolls and near‐surface streaks

Cited by 27 publications

References 18 publications

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Assessment of Surface-Layer Coherent Structure Detection in Dual-Doppler Lidar Data Based on Virtual Measurements

Transient Downslope Winds under the Influence of Stationary Lee Waves from the Zao Mountain Range

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