A Study of the Surface Layer Atmospheric Stability at Two UK Offshore Sites
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Transcript of 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 ArgyleCRESTLoughborough UniversityProf. Simon Watson
CRESTLoughborough University
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
Site Information
Shell Flats
Scroby Sands
Wind Speed & Direction
Temperature
Humidity
Atmospheric Pressure
Shell Flats
80m82m
70m
50m
30m
20m
12m
Scroby Sands
51m47m
33m
19m14m
•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
Considering Temperature
Virtual Temperature
(°C)
Potential Temperature (°C)
Data from Shell Flats site at 12m
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
Initial Results
Obukhov Length Stability Class Notation
-200 < L < 0 Very Unstable VU
-1000 < L < -200 Unstable U
1000 < L < -1000 Neutral N
200 < L < 1000 Stable S
0 < L < 200 Very Stable VS
Scroby Sands
Shell Flats
Number of events used for analysis
22585 7569
Percentage of collected dataset
38% 14%
Fre
quen
cy o
f O
ccur
renc
e (%
)
Scroby Sands Shell Flats
Wind Speed Results
Shell FlatsScroby SandsShell Flats
Wind Direction Results
Wind Direction
Dis
tanc
e to
Sho
re (
km)
Fre
quen
cy o
f O
ccur
renc
e (%
)Wind Direction
Dis
tanc
e to
Sho
re (
km)
Fre
quen
cy o
f O
ccur
renc
e (%
)
Scroby Sands Shell Flats
Monthly ResultsF
requ
ency
of O
ccur
renc
e (%
)
MonthF
requ
ency
of O
ccur
renc
e (%
)Month
Scroby Sands Shell Flats
Hourly Results
HourF
requ
ency
of O
ccur
renc
e (%
)Hour
Scroby Sands Shell Flats
Fre
quen
cy o
f Occ
urre
nce
(%)
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
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
Questions
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