An Analysis of Low-Frequency Maritime Atmospheric Turbulence

Gjerstad, Johannes; Aasen, Svein Erik; Andersson, Helge I.; Brevik, Iver; Løvseth, Jørgen

doi:10.1175/1520-0469(1995)052<2663:aaolfm>2.0.co;2

Cited by 18 publications

(17 citation statements)

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“…Since the 1990s, the deployment of tall masts at the seaside (Andersen and Løvseth 1995;Gjerstad et al 1995;Heggem et al 1998) or directly in offshore locations (Neckelmann and Petersen 2000;Holtslag et al 2015) has become more common. For example, the FINO1 met-mast, which was deployed in the North Sea in 2003 (Neumann et al 2003), provides high-frequency data from sonic anemometers at multiple levels above 40 m a.s.l.…”

Section: Introductionmentioning

confidence: 99%

Velocity Spectra and Coherence Estimates in the Marine Atmospheric Boundary Layer

Cheynet

Jakobsen

Reuder

2018

Boundary-Layer Meteorol

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Two years of continuous sonic anemometer measurements conducted in 2007 and 2008 at the FINO1 platform are used to investigate the characteristics of the single-and two-point velocity spectra in relation to the atmospheric stability in the marine atmospheric boundary layer. The goals are to reveal the limits of current turbulence models for the estimation of wind loads on offshore structures, and to propose a refined description of turbulence at altitudes where Monin-Obukhov similarity theory may be limited. Using local similarity theory, a composite spectrum model, combining a pointed and a blunt model, is proposed to describe the turbulence spectrum for both unstable, neutral and stable conditions. Such a model captures the −1 power law followed by the velocity spectra at an intermediate frequency range in the marine atmospheric boundary layer. For a Monin-Obukhov similarity parameter ζ < 0.3, the Davenport coherence model captures the vertical coherence of the horizontal velocity components well. A two-parameter exponential decay function is found more appropriate for modelling the coherence of the vertical velocity component. Under increasingly stable conditions, the size of the eddies in the vertical coordinate reduces, such that smaller separation distances than that covered in the present dataset may be required to study the coherence with sufficient accuracy.

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Section: Introductionmentioning

confidence: 99%

Velocity Spectra and Coherence Estimates in the Marine Atmospheric Boundary Layer

Cheynet

Jakobsen

Reuder

2018

Boundary-Layer Meteorol

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“…Some studies [e.g., Smedman‐Högström and Högström , ; Gomes and Vickery , ; Metzger and Holmes , ; Larsén et al , ] have confirmed its existence, although the gaps in their studies were not as pronounced as that of Van der Hoven []. However, other studies have discussed that the spectral gap is filled up with enhanced wind speed fluctuations, particularly when mesoscale structures, such as horizontal rolls, exist in the ABL [e.g., LeMone , ; Young , ; Gjerstad et al , ; Heggem et al , ; Lenschow and Sun , ; Vincent et al , ]. Recently, Larsén et al [] suggested that the horizontal wind variation from the mesoscale and microscale eddies yields the spectrum in the gap range.…”

Section: Introductionmentioning

confidence: 99%

Spectral structure of 5 year time series of horizontal wind speed at the Boulder Atmospheric Observatory

Kang

Won

2016

JGR Atmospheres

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We investigate the spectral structures of 5 year, 1 min time series of horizontal wind speeds at 100 and 10 m heights at the Boulder Atmospheric Observatory tower located in the eastern slope of the Rocky Mountains, USA. In the full‐scale spectra, the diurnal spectral peak, which is usually insignificant at a coastal or offshore site, is the most significant at both heights. The spectrum is enhanced on the low‐frequency side of the diurnal peak during winter, but on the high‐frequency side during summer, which indicates frequent synoptic weather events during winter supplanted by mesoscale events during summer. In terms of the spectral density in the spectral gap of Van der Hoven (1957), separating boundary layer turbulence from the synoptic‐scale fluctuations, at a frequency between 10−4 and 10−3 Hz, we rank the daily time series at 100 m height and sample the summer top and winter bottom 10 percentile cases. The winter cases of the reduced spectral density in the gap region present the f−3 spectrum (f is frequency) and negatively skewed velocity increment distributions, which are the signatures of enstrophy (the integral of squared vorticity) cascade of turbulent two‐dimensional (2‐D) flows. In contrast, the summer cases of the enhanced spectral density present the f−5/3 spectrum and positively skewed velocity increment distributions, which are the signatures of upscale energy cascade of 2‐D flows. In these mesoscale events that fill up the gap, the turbulence intensity‐wind speed relationship is very sensitive to the choice of the averaging period.

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“…These assumptions are shown in the figures 2, 3 and 4. Recent insights challenge these assumptions: the spectral gap in the Van der Hoven spectrum is absent over land (Courtney and Troen, 1990) and under unstable maritime conditions (Gjerstad et al, 1994), the distribution of wind speed variation is non-Gaussian (Böttcher et al, 2006), and wind speed profiles under maritime conditions differ from the Businger-Dyer profiles (Gryning et al, 2007 Figure 2. The classical assumption on the time variation of the wind speed.…”

Section: The Flow Towards a Wind Turbinementioning

confidence: 99%