Post on 02-Jan-2016
The Surprising Impact Stuff on the Tower has on
Meteorological Data
NUMUG MeetingChicagoJune 2011
Jim Holian, SAIC
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Tower, Conduit, and Equipment Impacts on
Wind Speed and Direction
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Wind-Speed Averages (Unobstructed)
Impact Hours A Avg. B Avg. Diff.
100-M
WS7433 13.9 12.8 1.4
60-M
WS7637 11.8 10.3 1.5
10-M
WS7754 7.8 7.0 0.9
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• Wind Directions from 195-245 degrees blow through tower
• Window is 25 degrees for vane and cup sensors and 30 degrees for sonic sensor
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Tower Interference
MO DY TM A100 B100 A60 B60 A10 B10 WD
4 30 12 13.0 13.4 12.9 13.0 10.7 10.6 192
4 30 13 12.3 14.6 13.0 14.9 11.9 12.4 209
4 30 14 16.6 10.8 16.4 11.8 14.5 9.7 224
4 30 15 22.3 11.9 20.5 13.3 17.9 9.8 238
4 30 16 19.4 9.5 17.9 10.8 15.3 7.8 234
4 30 17 25.8 22.4 23.1 21.1 20.2 17.1 261
4 30 18 16.5 13.2 14.2 11.6 12.1 8.8 252
4 30 19 14.7 9.3 12.4 8.4 9.7 6.1 235
Tower Interference - A Data Bad
MO DY TM A100 B100 A60 B60 A10 B10 WD
4 30 12 13.0 13.4 12.9 13.0 10.7 10.6 192
4 30 13 12.3 14.6 13.0 14.9 11.9 12.4 209
4 30 14 16.6 10.8 16.4 11.8 14.5 9.7 224
4 30 15 22.3 11.9 20.5 13.3 17.9 9.8 238
4 30 16 19.4 9.5 17.9 10.8 15.3 7.8 234
4 30 17 25.8 22.4 23.1 21.1 20.2 17.1 261
4 30 18 16.5 13.2 14.2 11.6 12.1 8.8 252
4 30 19 14.7 9.3 12.4 8.4 9.7 6.1 235
Tower Interference – B Data Bad
MO DY TM A100 B100 A60 B60 A10 B10 WD
4 30 12 13.0 13.4 12.9 13.0 10.7 10.6 192
4 30 13 12.3 14.6 13.0 14.9 11.9 12.4 209
4 30 14 16.6 10.8 16.4 11.8 14.5 9.7 224
4 30 15 22.3 11.9 20.5 13.3 17.9 9.8 238
4 30 16 19.4 9.5 17.9 10.8 15.3 7.8 234
4 30 17 25.8 22.4 23.1 21.1 20.2 17.1 261
4 30 18 16.5 13.2 14.2 11.6 12.1 8.8 252
4 30 19 14.7 9.3 12.4 8.4 9.7 6.1 235
10-m Wind-Speed AveragesTower Impact
Impact Hours A Avg. B Avg. Diff.
10-M
WS-A
394 7.7 8.1 -0.4
10-M
WS-B
225 7.1 4.3 2.8
60-m Wind-Speed AveragesTower Impact
Impact Hours A Avg. B Avg. Diff.
60-M
WS-A
364 9.8 10.3 -0.5
60-M
WS-B
285 10.5 6.6 3.9
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100-m Wind-Speed AveragesTower Impact
Impact Hours A Avg. B Avg. Diff.
100-M
WS-A
409 10.0 12.7 -2.7
100-M
WS-B
266 13.4 7.3 6.1
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Wind-Direction Averages (Unobstructed)
Impact Hours A Avg. B Avg. Diff.
100-M
WD
7375 184 182 2.6
60-M
WD
3970 184 180 3.6
10-M
WD
6148 195 189 6.7
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10-m Wind-Direction AveragesTower Impact
Impact Hours A Avg. B Avg. Diff.
10-M
WD-A
402 203 197 6
10-M
WD-B
80 243 236 7
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100-m Wind-Direction AveragesTower Impact
Impact Hours A Avg. B Avg. Diff.
100-M
WD-A
451 203 199 4
100-M
WD-B
145 240 235 5
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Electric Boxes atSensor height
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Pole Interference with Wind Speed
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Pole
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Antenna and Associated Conduit Interference with
Wind Speed
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Year Total Hours
Freq. (%)
A System (mph)
B System (mph)
Diff. (mph)
2009 1645 19.8 16.4 16.5 0.1
2007 1789 21.9 15.8 15.9 0.1
Average Wind Speed from Totally Unobstructed Directions (180°-230°)
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Year Total Hours
Freq. (%)
A System (mph)
B System (mph)
Diff. (mph)
2009 175 2.1 10.6 12.8 2.2
2007 103 1.3 11.9 13.0 1.1
Average Wind Speed Blowing Through Conduit to System A Sensor (355°-010°) with System B Sensor
Unobstructed
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Year Total Hours
Freq. (%)
A System (mph)
B System (mph)
Diff. (mph)
2009 145 1.8 12.3 13.7 1.4
2007 117 1.4 13.1 13.4 0.3
Average Wind Speed Blowing Through West Antenna to System A Sensor (345°-355°) with
System B Sensor Unobstructed
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Year Total Hours
Freq.
(%)
A System (mph)
B System (mph)
Diff. (mph)
2009 293 3.5 10.4 11.1 0.7
2007 199 2.4 11.3 12.7 1.4
Average Wind Speed Blowing Through West Antenna and Conduit to System B Sensor (010°-
025°) with System A Sensor Obstructed by Tower
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Year Total Hours
Freq. (%)
A System (mph)
B System (mph)
Diff. (mph)
2009 666 8.0 11.5 9.9 -1.6
2007 495 6.1 13.4 11.5 -1.9
Average Wind Speed Blowing Through South Antenna to System A Sensor (040°-060°) with
System B Sensor Obstructed by Tower
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Year Total Hours
Freq. (%)
A System (mph)
B System (mph)
Diff. (mph)
2009 920 11.1 14.1 13.5 -0.6
2007 654 8.0 13.9 13.7 -0.2
Average Wind Speed Blowing Through South Antenna to System B Sensor (065°-085°) with
System A Sensor Unobstructed
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Tower Interference with No Additional Equipment and
Limited Conduit
Dedicated Met Tower Concept
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Wind-Speed Averages – A System in Tower Wake
Impact Hours A Avg. B Avg. Diff.
10-M
WS162 4.6 4.5 0.1
60-M
WS97 4.1 4.7 -0.6
100-M
WS45 5.2 6.5 -1.3
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Wind-Speed Averages – B System in Tower Wake
Impact Hours A Avg. B Avg. Diff.
10-M
WS106 6.8 6.9 0.1
60-M
WS292 6.4 6.1 -0.3
100-M
WS189 7.2 7.1 -0.1
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What Caused 100-Meter Impact of 1.3 MPH?
• Close Review of data indicated almost 3 mph difference with wind directions from 339-347 degrees..
• This accounted for nearly all of the difference at the 100-meter level.
• Large Beacon Light is on north tower leg at top of tower.
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Conclusions
• Tower wake, equipment, and conduit have no measurable impact on wind direction.
• Greatest impact is on wind speed. Differences up to 10 mph seen at wind speeds above 20 mph.
• Obstructions such as antennas, beacons, and associated conduit have measurable impacts.
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Conclusions (cont’d)
• Dedicated meteorological towers have significantly less equipment and conduit and therefore have less interference.
• Having dual systems on separate faces of the tower appears to minimize wake effects due to spreading out of conduit, bracing, etc
• The data suggests that the sonic sensors may be influenced less by tower wake – not convinced.
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