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A Study of the Surface Layer Atmospheric Stability at Two UK Offshore Sites

A Study of the Surface Layer Atmospheric Stability at Two UK Offshore Sites. Mr. Peter Argyle CREST Loughborough University Prof. Simon Watson CREST Loughborough University. Outline. Site description and comparison

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A Study of the Surface Layer Atmospheric Stability at Two UK Offshore Sites

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  1. A Study of the Surface Layer Atmospheric Stability at Two UK Offshore Sites Mr. Peter Argyle CREST Loughborough University Prof. Simon Watson CREST Loughborough University

  2. Outline • Site description and comparison • Brief comment about humidity and temperature within the Monin-Obukhov similarity theory • Discussion on stability distribution with respect to • Stability changes with wind speed • Stability changes with wind direction • Stability changes with time

  3. Site Information • 1.5 year’s data at Shell Flats • 7 year’s data at Scroby Sands • 10 minute averaged data • Filter data to satisfy Monin– Obukhov assumptions 82m 80m 70m Wind Speed & Direction Temperature Humidity Atmospheric Pressure 51m 50m 47m Shell Flats 33m 30m Scroby Sands 20m 19m 14m 12m Shell Flats Scroby Sands

  4. Considering Temperature Data from Shell Flats site at 12m Virtual Temperature (°C) • Potential Temperature • Barthelmie 1999 • Virtual Temperature • Lange et al 2004 • Virtual Potential Temperature • Edson and Fairall 1998 • Peña et al 2008 • Sathe et al 2011 Potential Temperature (°C)

  5. Initial Results Frequency of Occurrence (%) Scroby Sands Shell Flats

  6. Wind Speed Results Shell Flats Scroby Sands Shell Flats

  7. Wind Direction Results Frequency of Occurrence (%) Frequency of Occurrence (%) Distance to Shore (km) Distance to Shore (km) Wind Direction WindDirection Scroby Sands Shell Flats

  8. Monthly Results Frequency of Occurrence (%) Frequency of Occurrence (%) Month Month ScrobySands ShellFlats

  9. Hourly Results FrequencyofOccurrence(%) Frequency of Occurrence (%) Hour Hour Scroby Sands Shell Flats

  10. Conclusions • Greater consistency is needed between site measurements • Similar instruments means similar variables can be compared • Similar heights makes comparison simpler • The marine atmosphere is rarely in neutral conditions • Monin – Obukhov similarity theory discards too much data

  11. References • Barthelmie: “The Effects of Atmospheric Stability on Coastal Wind Climates” Meteorol. Appl., 1999, 6, 39-47 • Lange, Larsen, Højstrup and Barthelmie: “The Influence of Thermal Effects on the Wind Speed Profile of the Coastal Marine Boundary Layer” Boundary-Layer Meteorol., 2004, 112, 587-617 • Peña, Gryning and Hasager: “Measurements and Modelling of the Wind Speed Profile in the Marine Atmospheric Boundary Layer” Boundary-Layer Meteorol., 2008, 129, 479-495 • Sathe, Gryning and Peña: “Comparison of the Atmospheric Stability and Wind Profiles at Two Wind Farm Sites Over a Long Marine Fetch in the North Sea” Wind Energy, 2011, 14, 767-780 • Edson and Fairall: “Similarity Relationships in the Marine Atmospheric Surface Layer for Terms in the TKE and Scalar Variance Budgets” J. Atmos. Sci., 1998, 55, 2311-2328 • Zilitinkevich, Johansson, Mironov and Baklanov: “A Similarity-theory Model for Wind Profile and Resistance Law in Stably Stratified Planetary Boundary Layers” J. Wind Eng. Ind. Aerodyn., 1998, 74-76, 209-218

  12. Questions ?

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