The nature and frequency of low wind speed conditions

Deaves, D.M.; Lines, I.G.

doi:10.1016/s0167-6105(97)00278-x

Cited by 24 publications

(40 citation statements)

References 3 publications

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“…For the southeastern portion of the U.S. the average wind speed is less than 3 m/s for half of the year and the same is true for most of the continental U.S. for the months of June, July and August [15]. Similar results have been reported in the United Kingdom [16]. A long duration measurement campaign over a pond at the DOE Savannah River Site (SRS) in Aiken, South Carolina shows a peak in the wind speed probability density function at u < 2 m/s [17].…”

Section: Introductionsupporting

confidence: 83%

A study of the Sherwood–Rayleigh relation for water undergoing natural convection-driven evaporation

Bower

Saylor

2009

International Journal of Heat and Mass Transfer

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Section: Introductionsupporting

confidence: 83%

A study of the Sherwood–Rayleigh relation for water undergoing natural convection-driven evaporation

Bower

Saylor

2009

International Journal of Heat and Mass Transfer

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“…Even if this is recognised, there is not a general consensus on how to define LWS. For instance, Smith (see Deaves and Lines, 1998) defined LWS as that in which the mean wind speed u is comparable to or less than the root-meansquare (rms) turbulent horizontal velocity r u . Based on this definition, they also suggested after examining several datasets, that this limiting wind speed ranges from 0.5 m s À1 in stable and neutral conditions to 1.2 m s À1 in unstable conditions.…”

Section: Introductionmentioning

confidence: 99%

“…Yamartino et al (1979) reported that in the region around Frankfurt, Germany, the annual average wind speed was found to be 2.2 m s À1 with wind speeds of less than 1.0 m s À1 occurring 25.2% of the time. Deaves and Lines (1998), on the basis of data from 1981 to 1990 from a selection of United Kingdom inland sites, showed that the annual average frequency of LWS conditions, defined as u < 2:05 m s À1 (4 knots), ranged from 9.2% to 29.7%. Agarwal et al (1995) reported that calm conditions occur quite frequently in the tropics.…”

Section: Introductionmentioning

confidence: 99%

An Analysis Of Sonic Anemometer Observations In Low Wind Speed Conditions

Anfossi

Oettl

Degrazia

et al. 2005

Boundary-Layer Meteorology

169

184

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When the wind speed decreases below a certain value (1-2 m s À1 ) 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 1 month, 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 r 2 y ðtÞ were also derived.

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“…Anfossi et al [11] point out that meandering (low frequency horizontal wind oscillations) begins to prevail when winds decrease below a certain level (1-2 ms -1 ) and that it becomes difficult to define a precise wind direction and to predict airborne dispersion. Deaves and Lines [12] suggest a lower limiting wind speed that ranges from 0.5 ms -1 in stable and neutral conditions to 1.2 ms -1 in unstable conditions. Wind direction differences were within ±7° and ±5° 90% and 80% of the time, respectively.…”

Section: Horizontal Wind Variablesmentioning

confidence: 99%

Improved Wind and Turbulence Measurements Using a Low-Cost 3-D Sonic Anemometer at a Low-Wind Site

Bowen¹

2008

TOASCJ

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A year of data from sonic anemometer and mechanical wind sensors was analyzed and compared at a low-wind site. Results indicate that 15-minute average and peak 1-second wind speeds (u) from the sonic agree well with data derived from a co-located cup anemometer over a wide range of speeds. Wind direction data derived from the sonic also agree closely with those from a wind vane except for very low wind speeds. Values of standard deviation of longitudinal wind speed ( u ) and wind direction fluctuations ( ) from the sonic and mechanical sensors agree well for times with u > 2 ms -1 but show significant differences with lower u values. The most significant differences are associated with the standard deviation of vertical wind fluctuations ( w ): the co-located vertical propeller anemometer yields values increasingly less than those measured by the sonic anemometer as u decreases from 2.5 approaching 0 ms -1 . The combination of u over-estimation and under-estimation of w from the mechanical sensors at low wind speeds causes considerable underestimation of the standard deviation of vertical wind angle fluctuations ( ), an indicator of vertical dispersion. Calculations of from sonic anemometer measurements are typically 5° to 10° greater than from the mechanical sensors when the mechanical instruments indicate that < 5° or so. The errors with the propeller anemometer, cup anemometer and wind vane, caused by their inability to respond to higher frequency (smaller scale) turbulent fluctuations, can therefore lead to large (factors of 2 to 10 or more) errors in both the vertical and horizontal dispersion during stable conditions with light winds. The sonic anemometer clearly provides more accurate and reliable wind data than the mechanical wind sensor with u < 2.5 ms -1 .

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The nature and frequency of low wind speed conditions

Cited by 24 publications

References 3 publications

A study of the Sherwood–Rayleigh relation for water undergoing natural convection-driven evaporation

A study of the Sherwood–Rayleigh relation for water undergoing natural convection-driven evaporation

An Analysis Of Sonic Anemometer Observations In Low Wind Speed Conditions

Improved Wind and Turbulence Measurements Using a Low-Cost 3-D Sonic Anemometer at a Low-Wind Site

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