HomeMy WebLinkAboutSUS48I
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WIND SPEED HEA5UREMENTS AND EXTREME WIND SPEED ESTIMATES
ANChORAGE-FAIRBANKS INTERTIE PROJECT
Prepared for
COM~ONWEALTH ASSOCIATES,INC.
Jackson,Michigan
February,1982
NORTHERN TECHNICAL SERVICES
ANCHORAGE.ALASKA
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RECEIVED
..o·1982
WIND SPEED MEASUREMENTS AND EXTREME WIND SPEED ESTIMATES
ANCHORAGE-FAIRBANKS INTERTIE PROJECT
Prepared for
COMMONWEALTH ASSOCIATES,INC.
Jackson,Michigan
February,1982
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TABLE OF CONTENTS
1.0 EXECUTIVE SUMMARY
1.1 General ..
1.2 Study Area
1.3 Method
L 4 Field Data
1.S Extreme Values
1.6 Extreme Wind Speed Isotachs
1.7 Conclusions .
2.0 THE STUDY AREA
2.1 Existing Climatological Data
2.2 Topography of the Study Area
2.3 Funneling ...
2.4 Mountain Waves
3.0 METEOROLOGICAL EQUIPMENT
3.1 WeatherMeasure WI02-P wind Speed Sensor
3.2 WeatherMeasure 8242-5 Barometer Sensor
3.3 Sea Data Logger Model 650-8 . . .
3.4 O.A.R.XF-SOI Series Flasher
3.5 Meteorological Towers and Permits
4.0 EXPERIMENTAL DATA ACQUIRED
4.1 Per iOO of Record . . . .
4.2 MAximum Wind Speeds Recorded
4.3 Prevailing Wind Direction
4.4 Gust Factors ....•
5.0 THE STATISTICAL MODEL
5.1 Experimental Plan
5.2 Surface Data
5.3 Upp'!r Air Data
5.4 Regression Results
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List of Variable Names
Meteorological Hindcast Study for
Alaska Power Authoritv,
Anchorage.Fa~rbanks Intertie Project
Route Selection Charts with
Extr~me Wind Speed Isotachs
TABLE 0F CONTENTS
(Continued)
EXTREME WINO SPEED ISOTACHS
7.1 General
7.2 Topographic Effects
EXTREME VALUE STATISTICS
6.1 Extreme Value Distributions
6.2 Length of Record Required for Reliable
Pred iet ions .......
6.3 Confidence Levels for Specified Design Life
APPENDIX 1
APPE DIX 2
APPENDIX 3
7.0
REFERENCES
6.0
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1.0 EXECUTIVE SUMMARY
1.1 General
Northern Technical Services (NORTEC)was contracted by Gilberti
Commonwealth to establish four wind speed/direction and baro-
metric pressure stations along the proposed Anchorage-Fairbanks
Intertie Project route and to develop a meteorological model for
evaluation and statistical summary report of extreme wind
cond~tions at specific locations along the route.
1.2 Study Area
The study area followed the proposed route along the Par.ks
Highway,Susitna River,Alaska Railroad and Nenana River from
Willow to Healy,Alaska.Along the route four site locations
were chosen in likely areas of high winds.These sites were
selected after careful study of the potential of the topogra9hy
for wind "funneling"and downslope effect.Site selection
criteria also included available climatological data,the
location of existing National Weather Service stations,the
acquisition of land use permits,and accessibility by road.The
locations selected along the Parks Highway were "Mile 243.3~
(Moody Bridge),"Mile 221.0"(Carlo River),~Mile 217.0"(Windy)
and "Mile 171"(Hurricane).
1.3 Method
Towers were erected at each site to provide standard 10 meter
heights for the Weather Measure Model W102-P Skyvane
anemometer,mountings for the Weather Measure 8242 ?ressure
sensor and Sea Data Corporation Hodel 650-8 data logger.
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1.4 Field Data
1.5 Extreme Values
Table 1 Maximum Wind Speeds Recorded:January-June 1981
Gust
MPH
125.1
117.5
78.9
Speeds
66.4
38.1
46.5
Maximum Wind
128 Sec Average
MPHLocation
Hile 243.3
Hile 221
Mile 217
The estimates of extreme wind wind presented in this report were
fitted to the Fisher-Trippett Type I Distribution:
Four wind data ste.tions ....ere programmed to record calculations
of two minute average wind speed/directions and gusts.Due to
intermittent failure of the Sea Data Logger (SOL)at -Mile 171-,
no usable data was obtained from this station.Maximum speeds
recorded during this program are shown in Table 1 below:
Wind speed and direction were sensed continuously and magnetic
recordings were made of the -128 second"average wind speed
direction and peak gusts.Barometric pressure was recorded
every hour.
Periodic visits to the stations were made at 30-,60-,and
90-day intervals to recover the data tapes,ins~ect the hardware
and replace the batteries.
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1.7 Conclusions
Table 2 Estimated Extreme Wind Speeds for various periods.
1.6 Extreme Speed Isotachs for the Transmission Line Corridor
The following specific conclusions have been drawn from this
study:
Estimated Extreme Speeds -MPH
Period 128-Sec Peak
YRS Average Gu!:t
25 99 178
50 104 188
100 109 196
25 55 142
50 57 150 .
100 60 157
25 78 13C
50 82 137
100 86 143
Mile 221
Location
Mile 243.3
Mile 217
Isotachs of the estimated 50 year,99'confidence extreme wind
speeds for the entire transmission line route have been drawn on
the route selection maps.These isotachs,representing our
professional jUdgment of the extreme speeds for the areas shown,
are based on the SO year extreme speed estimates made in this
report for the M.ile 217,221 and 243.3 locations,in our first
report for Summit and Talkeetna,and with qualitative
consideration for the topography of the area.
Application of this distribution,also known as a double-
exponential distribution,was made using the methods of
Gringorten and Simiu.
Table 2 indicates the estimates of extreme wind speeds
at each station for 25,50,and 100 year periods at the 99
percent confidence levels.
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(1)Highest average and peak gust wind speeds during the
period of measuremer.~were experienced during the winter months
of January,February and March.Weekly maximum speeds were much
lower during April,Hay and June.
(2)All of the highest winds speeds during the winter months
were from a southerly direction.At Mile 217 all gusts in the
70 to 79 MPH range (the fastest at this location)were from 130
degrees through 150 degrees.At Mile 221 all gusts over 70 MPH
were from 140 degrees through 240 degrees while all gusts over
100 MPa (7 cases)were from 180 degrees through 230 degrees.
At Mile 243 all gusts over 70 MPH were from 160 degrees through
220 1egrees while all gusts over 100 MPH (15 cases)were from
170 degrees through 200 degrees.
(3)At all locations,the gust factors were higher than guct
factors typicaily found at non-mountain~us locations.The
minimum gust factors were found to be l.7:~at Mile 217,2.57 at
Mile 221 and 1.62 at Mile 243.These gust factors are the
average for all speeds of the ratio of hourly maximum peak gusts
recorded to the hourly maximum average speed.They are minimum
gust factors since the maximum gust and maximum average speed
were not necessarily recorded during the same 128 second period.
Gust !actors during periods of very high peak gusts were higher,
especially at Mile 221 (sensor 8)where gust factors during
gusts over 100 MPH were approximately 3.0 to 3.5.
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2.0 THE STUDY AREA
2.1 Existing Climatological Data
In an October 1980 report,NORTEC reviewed available
c~imatological data for the proposed Willow to Healy
transmission line.Sufficient data was available to prepare
estimates of extreme wind speeds at Anchorage,Fairbanks,
Summit,Talkeetna and Healy.The Healy data was obtained from
records kept by Golden Valley Electric Association at their
Healy plant over a 2.4 year period.Although a 2.4 year period
is far too short to be meaningful for climatological purposes,
wind speeds of over 70 MPH had been recorded,resulting in all
estimates of extreme wind speeds at Healy being in excess of 100
MPH.Furthermore,on December 13,1967,a wind storm at Healy
had blown down 2 towers of an existing Healy to Fairbanks
transmission line even though these towers should have withstood
a 100 MPH wind.Because of the manner in which these towers
failed,investigators concluded that "wind loads of any
consequence on the line will be caused by turbulent high
velocity gusts of short duration rather than by steady winds."
Since the October 1980 study indicated the possibility of
unusually strong winds in the Healy area,Commonwealth
~s80ciates,Inc.contracted with NORTEC to install anemometers
to monitor wind speeds during the winter of 1980-81.
2.2 Topography of the Study Area
This study investigated wind speeds in the Nenana Gorge,a
valley one or two miles wide running approximately north-south
through the Alaska Range from Windy to Healy.The Alaska Range
curves in a nearly 500 mile long arc through southcentral
Alaska,passing just south of Healy in an approximately
east-west direction.Elevations along the valley floor are
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about 2000 feet,while peaks in the immediate area rise to 6000
feet.Within about 2S miles to the WSW and ENE,peaks rise to
about 75 miles to the wsw.The topography induces wind speeds
greater than would be expected from the large scale
meteorological situation through two mechanisms,funneling and
mountain waves.
2.3 Funneling
Sensors 7,8 and 15 were located in the Nenana Gorge,whicb
runs approximately north-south through the WSW-ENE oriented
Alaska range of mountains.Elevations in the valley reach
approximately 2,400 feet,while mountain peaks in the immediate
area are approximately 6,000 feet.within about 25 miles to the
wsw and ENE peaks rise to about 10,000 feet.Mt.McKinley,at
20,120 feet,is approximately 75 miles wsw.Thus,air flowing
from south to north at low levels is funneled through the Nenana
Gorge,with a resultng increase in speed over the unrestricted
flow.
2.4 Mountain Waves
While the Nenana Gorge is a funnel through the Alaska Range,it
is also in effect a mountain in itself.Approaching from the
south through Broad Pass,the elevation of the valley floor
rises to about 2,400 feet at Summit,the highest point in the
valley.The Gorg~then descends to an elevation of 1,300 feet
at Healy.According to Klemp and Lilley "The hydrostatic
mountain wave is one oe the important wave forms generated in
stable air passing over mountainous terrain having a character-
istic width of 50 to 200 km".l They further note that "At
certain locations in the lee of large mountain ranges,intense
and damaging surface winds arise when these waves attain large
amplitude".Winds of this nature are often observed in the
Boulder,Colorado area,where these severe downslope wind storms
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have,during several recent winters,resulted in winds of over
100 MPH.A storm during January 1982 resulted in over $10
million damage in the Bould~r area.Wayne Sangster,of the
National Weather Service,has developed an objective forecast
technique for Colorado downslope winds.2 Sangster,using
regression to identify predictors of strong downsl~pe winds,
found that vertical temperature differences and preS&ure surface
height differences were important.Brinkman,investigating
Boulders wind storms,found that ~Upper air conditions favorable
for Boulder's wind storms were found to be the existence of a
stable layer above the mountain top and a less stable layer
above that.Winds are high at the level of the stable layer
but,contrary to general belief,strong winds in the upper
atmosphere are not necessary-.3 Also,-At the surface,a
strong pressure gradient across the mountains is clearly
important but roay be superimposed upon either a general pressure
rise or fall.-.
Size:
Propeller:
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3.0 METEOROLOGICAL EQUIPMENT
A diagram of the meteorological measuring equipment installed at
each site is shown in Figure 1.Figures 2 through 5 show the
actual site locations at different times of year.Detail
descriptions of the sensors and data acquisition system follow.
3.1 Weat~er Measure WI02-P Wind Speed Sensor
The WI02 Skyvane I Wind Sensor is designed to withstand severe
environments such as icing and hurricane winds.wind speed is
measured by means of a four-blad~d propeller which is coupled to
a DC generator.The balanced propeller fabricated of a special
low density fiberglas-reinforced plastic to yield a maximum
sensitivity and strength.The DC generator is used in
applications where a rectifier circuit is not practical.It has
excellent linearity but somewhat higher threshold due to brush
friction.Dual wiper precious ~etals slip rings are used to
bring the wind speed signals to the base of the sensor.These
have been essentially trouble-free after many years of use,even
in adverse environments.Wind direction is measured by means of
a dual wiper 1000 ohm long life conductive,plastic potentio-
meter housed in the base of the sensor.It is attached to the
stainless steel shaft which supports and rotates with the upper
body assembly.The sensor body is constructed from fiberglas
reinforced plastic mounted on a cast aluminum base.
Specifications
29 3/4L x 30"8
4 Blades,13 3/4",Fiberglas reinforced
plastic
Starting Speed:1 MPH (0.45 m/s)
Complete Tracking:3 MPH (1.35 m/s)
Maximum Speed:200 MPH (91 m/s)
Wind Speed Sensor:DC generator:15VDC @ 100 HPH(45.S m/s)
Distance Constant (30 MPH(13.6 m/s)):6.2'(1.9m)
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n__---WARNING LIGHT FLASHER
l=~=1j __--WEATHER MEASURE
WlQ2 ANEMOMETER
1-_-SEA DATA 6~O·8
MICROPROCESSOR
1-_---12 IN.DIAMETER
TELEPHONE POLE
CONFIGURATION OF 10·METER
REMOTE METEOROLOG ICAL STAT ION
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WEATHER MEASURE
0-242-5 ANEROID
BAROMETER-------------U
12 YOLT BATTERy---1
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Figure 2.Meteorological Station Mile 243.3 (Moody Bridge)
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Fi~ure 3.Meteorological Station Mile 217 (Windy)
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.......'..
•...J"'":....,.~-~"",.""'-
.--.
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Figure 4.Sea Data Logger at "t-1ile 172"
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Figure 5.Barometric Pressure Sensor at Station "Mile 172"
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Accuracy:+1%below 25 MPH (9.1 m/s);
+3'above 2S MPH (9.1 m/s)
Time Constant (30 MPH(13.6 iR/~.l):0.145 sec.
Wind Speed Sensor:1000 conductive plastic potentiometer,
dual wiper -standard.Other values or
s1ne-cosine on special order.11SVAC
selsyn motor may be substituted.
Weight/Shipping Weight:11 3/4 1bs./25 1bs.
(5.3 Kg/11.4 Kg)
3.2 weather Measure 8242-5 Barometer Sensor
The Model 8242-5 contains a multicell aneroid sensor which
positions the core of a linear variable differential
transformer (LVDT).The output voltage of the LVDT,which is
linear with core position (hence with pressure),is amplified to
the level desired.All mechanical and electrical components are
designed to achieve linearity and a low temperature coefficieflt.
The aneroid cells are of NiSPAN-C and have a thermal expansion
coefficient of essentially zero.
The gain and zero point of the amplifier may be adjusted to
produce an output varying from 0 to 1 VDC over any 100 mb
interval between 600 and 1065 mb.The gain is normally set at
the factory and the zero point set in the field to correspond to
the elevation of the installation.
The sensor housing is airtight and provided with a pressure
fitting so that atmospheric pressure in the range of 600 mb
(to 1050 MB)may be measured.
Specifications:
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Range:
Linearity:
Resolution:
Ambient Temperature:
Power Required:
Output:
Any 100 mb interval from 600 to 1065 mb
+0.5 mb over 100 mb interval (0-40·C)
Infinite
-20 to 40·C
10 to 12 VOC
o to 0.2 VOC
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3.3 Sea Data Logger Model 650-8
The Model 650-8 Data Logger is designed to record the amplitudes
of a number of analog inputs at regular intervals.Both the
number of channels to be recorded and the recording interval are
determined by the setting of rotary switches on the front panel
of the logger.In the recording process,the analog inputs are
first digitized and then recorded on a cassette tape,along with
a time word plus a record header that records the measurement
rate switch setting and 11 additional parallel inputs.High
density recording methods are used,making it possible to record
a&many as 16 analog inputs once every minute for 40 days,with-
out exceeding the capacity of a 450'cassette tape.
High density recording in the 650-8 is accomplished by using
four cassettp tracks,and shortening inter-record gaps through
the use of a stepping motor drive.These two devices make it
possible to write 10 megabits of data on a 300'cassette without
increasing the writing density per channel above 800 bpi.High
density writing is thus accomplished without sacrificing
reliability.The recorder electronics employs all C-MOS
circuitry to minimize power drain,yielding a typical power-off
drain of less than 0.8 rnA for the 650-8.
The cassette transports a~~built on precision machined
castings,ensuring the close tolerances necessary for high
reliability.In addition,the unusual four-track head is
mounted with cast and precision-ground guides for accurate tape
guiding.Finally,a tough industrial 200 step per revolution
stepping motor with unique 8-phase current-source drive yields
trouble-free tape motion for the 800 bpi phase-encoded
recording.
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Timebase Accuracy:
Data Storage Medium:
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1 to 2048 sec in 12 steps
15 msec per channel
8 single-ended analog
Each channel is converted to a 12-bit
binary word
-5 to +5 volts standard
Switch selects 2,4,6,f,(12 or 16)
channels
Glass-epoxy terminal strip on rack for
ccnnection to user-wired endcap penetrator
pigtails
Standard digital certified 300'or
450'cassette tapes
10 megabits on 300'cassette yielding
536,000 12-bit data
12 parallel-input bits from user
4 bits showing time switch setting on front
panel
20-bit internally-generated time word
4 or 8 analog 12-bit data channels--panel
selected
4 parity bits (one for each track)
16.384 kHz quartz crystal
Stable to +/-10 ppm over lO·C to 40·C
Correctable to +/-5 ppm over.-s·C to +5S·C
SBD-4 Sea Data 15 volt,20 Ahr Alkali~e battery pak
12"long by 5.8"diameter
10 pounds,including Alkalin ....SDB-4 battery
Format:
Capacity:
Power:
Rack Size:
Weight:
Connectors:
Input range:
Selector:
Scan Interval:
Channel-scan Rate:
Channels:
Resolution:
The O.A.R.XF-500 Series of Surface Flashers are high-intensity,
gener~l purpose xenon markers designed to aid in relocation of
surface objects such as buoys,towed and stationary platforms,
free-floating instruments,etc.A xenon gas diacharge ~amp
element gives a high-intensity 0.1 watt-second flash at a rat~
of 1 flash e~ery 2 seconds (standard settings)that can be seen
at horizoAtal distances of 6 to 10 miles under clear,dark
atmospheric conditions.Slant visibility range from aircraft,
under similar operating conditions is up to 25 miles.The unit
has a clear,solid plastic lens installed on top of a cylin-
drical pvC case.It is designed for short or long term
operation in the marine environment.Lamp-life is estimated to
3.4 O.A.R.XF-501 Series Flasher
Specifications:
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3.5 Meteorological Towers and Permits
be in excess of 1 year of continuous operation (at standard
output level and fl~sh rate setting).Design configurations are
available for operation from self-contained or external DC
power,and unit dimensionsl weight vary accordingly.Flash rate
settings of 1 flash/second to 1 flash/4 seconds are optional,
along with increased or reduced light intensity level.
Land use permits and installation of la-meter towers were the
responsibility of Dryden and LaRue Consulting Engineers.The
towers were standard telephone poles approximately 35 feet long.
Height of the anemometer was adjustable when nlounted at the top
of the telephone pole to insure the proper distance (la-meters)
above the ground.Data loggers,barometers and batteries were
mounted on the side of the telephone pole at a height of
approximately six feet above the ground.
Typically 0.01 lumen-second/flash/foot 2
at a distance of 2 feet
0.1 Joule (watt second)minimum
Type -Xenon gas discharge
Standard - 1 flash/2 seconds
Standard -Photocell shutoff circuit turns
lamp off during normal daylight hours
Standard -12VDC @ 20 rna
Latest solid state components
Sealed PVC tubing case with solid,clear
plastic lens.Mounting collar with I 1/4"
male pipe threads.Stud-type power input
terminals.
0.5 pound (250 grams)Weight:
Power Input:
Lamp:
Flash Rate:
Duty Cycle:
Power Supply:
Electronics:
Construction:
Specifications:
Light Output:
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4.1 Period of Record
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4.0 EXPERIMENTAL DATA ACQUIRED
Table 3 Maximum Wind Speeds Jan.8 -June 10,1981.
78.9
117.5
125.1
46.5
38.2
66.4
Maximum Wind Speed-MPH
Sensor 7 Mile 217 Parks Hwy.
Sensor 8 Mile 221 Parks Hwy.
Sensor 15 Mile 243.3 Parks Hwy.
The maximllin wind speeds recorded during the experiment are
shown in Table 3 below.
4.2 Maximum Wind Speeds Recorded
Acquisition of data began January 8,19B1.All sensors were
inoperative during the period Februa~y 14 through February 19.
1981,apparently due to low temperatures (approximately -30·F)
in the area.However,synoptic data indicates the winds in the
area would be light during that period.Sensor 7 recorded data
through the week of May 14,sensors 8 and 15 recorded data
through the week of June 4,1981.
weekly maximum wind speeds are tabulated below for each sensor.
All maximum speeds recorded during the experiment occurred
during January or February.Furthermore,the weekly maximums
showed a sharp decline at the b~ginning of April.
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TABLE 4 Weekly Maximum Wind Speeds Recorded in MPH.
Maximum Peak Maximum Peak Maximum Peak
Average Gust Average Gust Average Gust
Week Dates t7 t7 '8 '8 U5 U5
1 1/8-1/14 33.9 61.1 30.5 106.4 50.9 85.9
2 1/15-1/21 36.0 64.1 38.2 117.5 55.0 92.8
3 !/22-1/28 39.4 68.0 28.2 98.4 51.8 93.4
4 1/29-2/4 46.5 78.9 29.6 87.4 66.4 1<8.3
5 2/5-2/11 27.9 42.6 28.0 60.8 46.3 78.2
6 2/12-2/18 32.1 54.4 19.8 33.0 12.6 18.6
7 2/19-2/25 28.8 49.2 33.8 84.3 66.0 125.1
8 2/26-3/4 36.8 65.7 31.8 94.7 64.8 112.4
9 3/5-3/11 34.4 61.5 21.8 62.0 40.9 69.9
10 3/12-3/18 39.2 69.4 30.2 85.2 50.3 82.9
11 3/19-3/25 32.2 46.5 18.8 40.2 33.5 50.8
12 3/26-4/1 20.7 36.3 21.7 40.3 42.7 71.6
13 4/2-4/8 25.4 48.3 15.2 29.9 29.7 M
14 4/9-4/15 31.0 41.9 18.5 34.7 29.2 M
15 4/16-4/22 20.2 33.8 18.6 31.7 32.6 M
16 4/23-4/29 19.3 30.4 14.1 20.9 27.6 M
17 4/30-5/6 27.2 43.0 22.3 43.5 43.5 M
18 5/7-5/13 19.9 31.3 20.7 39.8 26.0 M
19 5/14-5/20 25.3 39.6 21.7 32.7 46.4 M
20 5/21-5/27 M M 18.8 29.5 29.7 47.9
21 5/28-6/3 M M 18.8 29.5 28.9 48.3
22 6/4-6/10 M M 22.5 31.6 39.3 64.5
4.3 Prevailing Wind Direction
A two-way frequency table of wind direction versus wind speed
(both average and peak gust)prepared for each site using the SPSS
"CROSSTABS"procedure is illcluded in the Appendix.(In referring
to these charts note that wind speeds in MPH are labelled across
the top.)At each site the strongest winds were from the souther-
ly quadrant.For example,at sensor 15,which experienced a
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maximum wind of 125.1 MPH during the experiment,the peak wind
speeds from northerly directions (270·through 090·)were less
than 30 MPH.At sensor 15 all peak gusts of 60 MPH or more were
from 150 degrees through 220 degrees,all gusts of 100 MPH or
more (15 hours total)were from 170 degrees through 200 degrees.
Also presented are simpler,but less informative,histograms ~f
wind speed versus direction for each site.The histograms of
direction of average wind speed include only those cases in
which the wind speed was greater than or equal to 30 MPH,the
histograms for direction of peak wind speed include only those
cases with gusts greater than or equal to 40 MPH.Note that
SPSS prints only the directions for which cases occurred.Thus,
for example,the histogram for PKDIR 15 shows the frequency of
hourly recordings for codes 14 through 22,representing
directions 140 degrees through 220 degrees.No gusts of 40 MPH
or mere were recorded from directions 230 degrees clockwise
tilrough 130 degrees (Codes 1 through 13 and 23 through 36),as
indicaced by an absence of these codes.It's interesting to
note that sensor 7 had 296 case:,sensor 8 had 394 cases,and
sensor 15 had 844 cases of gusts >40 MPH.Average ind speeds
were greater than or equal to 30 MPH for 114 cases at sensor 1
15 cases at sensor 8 and 634 cases at sensor 15,out of approxi-
mately 1,650 cases.
4.4 Gust Factors
!n order to evaluate the gust factors at the 3 sites the SPSS
Scattergram procedure was used.This procedure produced the
graph shown in Appendix (TAB -GUST-)in which P7,sensor 7
maximum peak gust wind speed is plotted against A7,sensor 7
average wind speed.Scattergram does linear regression of p7
against A7,and,in this case the statistics indicate a
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regression equation of P7 :1.72 *A7 -1.09.The constant term
in this equation should be zero of course,but -1.09 is quite
close.The slope,1.72,indicates that the average wind speed
should be multiplied by 1.72 to find the corresponding gust
speed.The Scattergram for sensor 15 produced very similar
results,with a slope of 1.62.~t sensor 8 the slope was
co~puted to be 2.57.
At all sensors,the maximum average wind speed was the greatest
128 second average wind speed recorded during a given hour.The
maximum peak wind speed is the maximum instantaneous wind speed
recorded during the same hour.However,it is not possible to
determine from the data if the maximum average and the maximum
peak wind speed occurred during the same 128 second period of
each hour.Therefore the slope of each regression equation
represents a minimum gust factor.In general it seems likely
that maximum peak wind speed would occur with the maximum
average speed.However the appearance of the P8/A8 Scattergram
creates room to sp~cu1ate if this is always the case.In
examining the graph keep in mind that 1644 cases were plotted,
and the SPSS prints a star for each plotted case,the number 2
through 8 when 2 through 8 cases occupy the same location,and
the number 9 when 9 or more cases occupy the same location on
the graph.The large majority of the cases are concentrated in
the area where PB is less than 50 MPH,and these cases also
account for the majority of input to the R-square of .82.
Therefore,in some instances it appears that the gust factor at
sensor 8 ~lS 3.0 or greater,and that a linear relation between
gust and average speeds at sensor 8 during gusts above 80 MPH
did not exist.
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5.0 THE STATISTICAL HODEL
5.1 Experimental Plan
The essential feature of thi~method is the correlate the wind
speed ob~erved at these sites with surface and upper air
meteorological parameters recorded at surrounding locations
having long periods of record.The correlation was accomplisheo
using the multiple,linear,least-squares reqression procedures
of the Statistical Package for Social Sciences (SPSS).The
overall plan of the model is shown in Figure 2.
5.2 Surface Data
Surface pressure differences were the first parameters
investigated since wind is the result of pressure differences,
and begins to flow from areas of high atmospheric pressure to
areas of low atmospheric pressure.However,the wind is
deflected to the right by coriolis force,and thus flows
clockwise around areas of high pressures and counterclockwise
around areas of low pressure.Therefore,since we have
established that the strongest winds in the experimental area
are always approxim~tely southerly,we would expect to correlate
those wind speeds with east-west surface pressure differences
generated by low pressure systems located south or west of the
Healy area.While there are no ideally located weather
observing stations for measuring east-west gradients in the
experimental area the following pressure differences were
investigated:Anchorage-Valdez (AV),Anchorage-Gulkana (AG),
Fairbanks-Big Delta (FB),Fairbanks-Gulkana(FG),and Fairbanks-
Summit (FU).However,only intermittent 1981 data was available
for Summit,and the period of record for Valdez (since 1976)was
much too short,so AV and FU were deleted from the regression
equation.
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II .cc-·,.,·.!~~•••·,.'"zo..~J~a.a.'"II
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•-..-.,-c.-c c~-,--•--•,:;c,-:;~~•c~c ,.,>·~•"':~c ~c ·c>,-c"_,-0 c 'c .~o'•-.-~c•c~c •C,••,·•-.C.-'c C-•!••·,'0 >~-:;C.•-•-~.~,'.,•,,~c _c .0
"-c .-,C'2 ...03 --=-c c~,"c c.',.-_c-...~~--,c-c-.c.sS"
,
:;c "c %!..".',c 8 •-":~~.·•-,~.•c ;EZ c z z -"',•:la:...-cc_~-c•-'~--.~~.B:::..~>c-8;co'2.e~..,_.
>.c
~..c,-..".0_c_.,.;•.~.••.~.
•
.;~_c .c0_c-,"".co C Cc
--..c'oc '."c ,.!•,-.'c:;~~"0..,cOc'_,0 c~a:.,'--'--,c .-c ._..
00'..c_~,
~...:;...z.~,-,,-!,!;;;;,••:=,..0o'•cc -.0 •'0 ••,,•~,.,--,c ,,.-•.c c.-c·~8~~0'""0 coc'a••
I I
c_,··~:;•-,'".'~••0 O'·C
~.•,--••-·~•-.,0 ,•·-•....~•0 •z ~,•·i -..•••,
0 ,z ¥0 0 •,0 •c ~~-.••-•,,c 0 ,!•.•••,>•,•00 •·c ,·;;_.
=
c _,c·•,.0 ••~c ••oc.••0 c_•
"0
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5.3 Upper Air Data
Because of the possibility of the funneling and mountain wave
mechanisms previously described,upper air data was selected
for the regression equation.Initially,the height,
temperature,relative humidity,wind direction,and wind speed
from the 850 millibar,700 millibar,and 500 millibar levels
were included.Later progtam "Finsert"was developed that
calculated the l~pse rate of every reported layer in the upper
air observations between 900 and 500 rob and sorted the layers in
order from the most stable to least stable.Therefore,the
height,pressure,thickness,temperature lapse rate,base
temperature,rel~tive humidity,wind speed and wind direction of
the 6 most stable layers were incorporated into the regression
equation.A complete list of variable names and definitions is
given in Appendix 1.
5.4 Regression Results
The complete regression results have been included in the
Appendix 2.As an example,we examine the regression of P15
against the surfac~and upper air variables (see tab marked
"P1S REGR SUM").As seen on Page 10 of the SPSS output there
were 1841 cases.The mean and standard deviation of each
variable are shown here,r.ote the PIS had a mean speed of 38.67
MPH.Regr£·ssion results are shown in the summary table on P-27
of the output.The best single predictor of PIS is entered into
step 1.In successive steps additional variables are entered in
order from the greatest improvement of the R square,in
conjunction with the variables already in thp.equation,to the
least improvement in R2.We note that FG,the Fairbanks-
Gulkana pressure difference,is the be~t single predictor of the
peak wind speed at sensor 15.ATS8,the Anchorage 500 mb
~emperature -the Anchorage 800 mb temperature,is entered in
step 2 since it increases toe R square by .05182,even though
an R of .02128 indicates there is virtually no direct
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correlation between PIS and AT58.The simple R of A7Y,entered
on step 3,is -.66683,indicating nearly as good ~correlation
with PIS as FG has.The 60th step indicates an R2 of .74529.
That is,the regression equation explains 74%of the variation
in wind speed.
After many runs,experimenting with different variables,the
following results were obtained.
R-SQUARE
A7 P7 AS P8 A15 P15
Upper Air Data Only .62 .64 .56 .64 .68 .69
Upper Air and .64 .67 .58 .65 .73 .74
Surface Data
Since the inclusion of surface data resulted in only a 2 to 5
percent increase in the accuracy,it was decided to use only
the upper air data in calculating the estimates.
The results of the regressions for each sensor using only upper
air data are shown in Appendix 2.We not.e that A7Y,the Y
component of the Anchorage 700 mb wind speed,is always the best
single predictor of site wind speed.
5.5 Calculation of the Estimates
Upper air data for Anchorage and Fairbanks for the period 1948
through 1979 was obtained from the National Weather Service.
Six programs,EA7UA,EP7UA,EA8UA,EA15UA,EP15UA,were prepared
to calculate the estimates of average alld peak wind speeds at
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each site.The 6 programs were identical except for the
coefficients of the predictor variables.Each program
calculated an estimate of the site wind spe~d for every
12-hourly upper air observation from 1948 through 1978.
However,1948 and 1949 were found to have considerable missing
data,making it impossible to calculate the estimates about hale
the time.Therefore,estimates from these years were not used.
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6.0 EXTREME VALUE S~ATISTICS
6.1 Extreme Value Distributions
The three distributions that have been used to model extreme
wind speeds are:5
1.The Fisher-Tippett Type I Distribution:
The Type I distribution was used by Gumbel.The double-
exponential distribution advanced by Gringorten as
generally best for extreme values in the Type I distribu-
tion.The National Building Code of Canada assumes a Type
I distribution of extreme wind speeds.
2.The Fisher-Tippett Type II Distribution:
F(V)•exi'[ -(V ;''fY ]
Also known as the Freehet Distribution,the '.ype II
distribution has been advanced by Oa?enport and Thorn for
use in describing the distribution of extreme wind speeds.
Type II distribution is assumed by certain American
National Standards.If Y =II),a Type II distribution
reduces mathematically to a Type I distribution.
3.The weibull distribution:
[-(Vo'.U)r ]F(Vj=l-exp r
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A Weibull distribution with ~~2 is called Rayleigh distribu-
tion.
In all three distributions u is called the location parameter,
because it specifies the location of the center of the distri-
bution4 Usually V ,the mean of the observed extreme wind
speeds,is used to approximate p.The scale parameter or is a
measure of how ·spread out R the distribution is and is usually
approximated by the standard deviation ~of the observed extreme
speed.The shape parameter",of the weibull and Type II
distributions,sometimes called the tail-length parameter,can
be determined empirically from the data.
The applicability of Type I and Type II distributions to annual
extreme wind speeds was investigated by Simiu.5 After
calculating both distributions for 21 locations in the United
States,Simiu concluded that no single distribution was
universally applicable to all locations.However the Type I
(double exponential)distribution provided the best fit in 45%
of the cases,while the Type II with various values of
provided the best fit in the remainder.Best fit was determined
by the distribution having the highest maximum probability plot
correlat~on coefficient.
Simiu's publication provided the FORTRAN code to fit Type I and
Type II distributions to extreme data.The resulting proba-
bility plot correlation coefficients,taken from the output
included in Appendix 2 and shown in Table 5,indicate that data
from sensors 7,8 and 15 was best fit by a Type 1 distribution.
Therefore,the estimated extreme wind speeds in Table 2 are
based on a Type 1 double exponential distribution.
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TYPE TYPE OPT mUM
I II GAMMA
Location
Sensor 7 Average Speeds .988 .974 10
Sensor 7 Peak Speeds .992 .975 14
Sensor 8 Average Speeds .989 .982 Infinity
Sensor 8 P.eak Speeds .985 .970 3
Sensor 15 Average Speeds .992 .974 Infinity
Sensor 15 Peak Speeds .989 .968
Infinity
Table 5 Probability Plot Correlation Coefficients.
Therefore the Type I distribution provided an excellent,and the
best,fit to the estimated data.
6.2 Length of Record Required for Reliable Predictions
Simiu investigated the length of records required for reliable
extreme value predictions using 37 year records from 21 U.S.
locations.These records were broken into 30,25.and 20 year
overlapping records that were separately analyzed.At those
locations where Type I distribution was optimal,Simiu found an
average difference of 39%between the largest and smallest 1000
year return period estimate calculated from separate 20 year
portions of.the 37 year record.Errors in e~timates for very
long return periods are significant because,as explained in
Section 6.3,a SO year 99~confidence estimate requires a 5000
year return period estimate.
-29-
6.3 Confidence Levels for Specified Design Life
Since it is certain that the design maximum value will either be
exceeded or not be exceeded during a given year
Let x ~the design maximum value of a climatological
parameter (precipitation amount,wind speed,etc.)
p 3 the pro~ability that the design maximum value will
be exceeded during a given year
p(x)=probability that the design maximum value will not
be exceeded during a given year
In order to design a structure to withstand various climato-
logical extremes for a given ~riod of time appropriate design
values must be determined.For example,it is likely that a
structure with a 50 year life will have to withstand wind speeds
greatly in excess of the 50 year return period wind speed.To
determine what return period a structure should be designed for,
consider the following:
( 2 )
(3I
( 1 )
(or mean recurrence interval)
1
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R =1 -pIx)
period
1
p
R
Rl-p(x)=
p(x)=l-
p+p(x)=l
P = 1 -pIx)
by substitution from (1)
We define R =return
rearranging
Prom Simiu 6 R =
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Since we know P(X),th~probabilitj of the value ·X"not being
exceeded during a given year,we can find the probability of ·X·
not being exceeded during N years.
To begin with,we note that the probability of two independent
events both occurring is given by:
I P(AOB)P(A)P(B)(4 )
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Therefore,for eX3mple,the probability,P2,of v not being
exceeded during a 2-year period is the probability of V not
being exceeded during one-year times the probability of V not
being exceeded during one year,or,
P2 •p(X)•p(X)•(p(X))2
similarly for 3 years
P3 •p(x)•p(X)•(p(X))3
For N years,where we define PN as the probabili~y that X will
not be exceeded during the N-year period:
I (5)
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For example,suppose that X 2
1
and R=1_peal ""50 years.
wind is 100 PlPH.If we wish
wind will not exceed 100 MPH
apply equation (5).
100 MPH,p(x)=.98,p=1-p(x)=.02,
That is,the 50 year return period
to find the probability that the
during any given la-year period,we
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PN'(p(X))N.(.98)10 ••817
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That is,there is an 81.7%chance that the wind will not exceed
100 MPH du~ing a 10 year perio~.Since we have taken as our
example a 50 year return period wind,it is interesting to note
that the probability of 100 MPH not bei~9 exceeded during any 50
year period is
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P N Z (pIX))N z (.98)50 ~.364,
Thus there is a 36.4 chance that 100 MPH wi.1 not be exceeded.
Therefore there is a 1-.364,or a 63.6%chance,that ~OO MPH
will be exceeded during the 50 years.It can be shown that
during any period of N years there is a 63.6%chance of the N
year return period wind speed being exceeded by at least
once.7
I
We can find the return period needed to assure a speciried
confidence level as follows:
I From EO (S)
1 1"0 ;-
I
"0 ;
1
"0
';
[P NJ N
1 -
By substitution from EQ 3
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Therefoce,we have found the required return period,RO'of
the de~ign maximum value of X ~n terms of the probability,PN
of the design windspeed not being exceeden ~urin9 the period N.
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For example,if we want to find a value X that will have a 95~
probability of not being exceeded during any 50 year period,we
are declaring P =.95 and N~50 years.Therefore:
=4975 years.
:;975...years ••••1-[95]
"-[99],.
"l-[...]'·
RO •
Therefore the 50 year estimates used in this report are taken
from the 5000 year return period values on the output of program
"Extreme".Repeating the ab;)ve calculation shows that for a 25
year life a 2487 year return period should be used,while for a
100 year li~e a 9,950 year return period is used.
We therefore would calculate using the double-exponential
function th~value of X having a return period of 975 years to
se as the 95 percent confidence value for a 50 year period.
Similarly,to calculate the 9~'confidence values used in this
report for 50 year life periods,we calculate:
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7.0 EXTREME WIND SPEED ISOTACHS
7.1 General
Estimates of the 50 year,99%confidence,extreme wind speed for
the entire transmission line route in the form of isotachs have
been drawn on the route selection maps.These isotachs,
representing our professional judgment of the extreme speeds for
the areas shown,are based on the 50 year extreme speed
estimates made in this report for the sensor 7,8 and 15
locations,the estimates in our first report for Summit and
Talkeetna,and with qualitative consideration for the topo-
graphic effects outlined below.
7.2 TOpographic Effects
The topography of an area influences wind speed through several
mechanisms.Topographic features indicative of high wir.j speeds
are:
1.High elevation plains and plateaus will have higher wind
speeds than similar flat low elev~tion areas,but are
unlikely to experience extraordinary extreme wind values
because of the absence of wave or downslope mechanism over
the flat terrain (see 14).
2.Exposed mountain summits and ridges in areas of strong upper
air winds.Again downslope effects,and funneling,will be
absent in this case.Therefore exceptionally s~rong winds,
i.e.100 MPH plus,would only be likely at elevations above,
say,10,000 ft.
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3.Gaps,passes and gorges through mountain barriers in areas
of frequent strong pressure gradient may experience wind
speeds in excess of the pressure gradient wind due to
funneling of the wind through the opening.Parameters
determining the amount of increase in wind speed resulting
from f~nelin9 include
a.height of the mountain barrier
b.cross-sectional area of the funnel opening
c.shape of the funnel opening
d.roughness of the funn~l surface
4.The lee (downwind)side of mountain ranges.frequently
experience extremely strong winds known varlously as
mountain wave,downslope,foehm and bora winds.The winds
occur on the lee slcpes of the mountains,and may extend a
short distance (10-20 km)out onto adjacent flat areas.The
several theories advanced to explain the mechanism of these
wi;lds involve the generation by the mountain range of wave
motion in the stratified flow of the atmosphere under
certain atmospheric cond~tions.The following observations
and results have been obtained:
a.A.mountain wave numerical model Lndicates that the
surface wind sp~ed has its maximum half-way down the lee
side of the mountain when atmospheric conditions for the
formation of a wave are optimal.4 The point of
maximum wind speed will move further downstream under
certain non-optimal conditions.
b.The numerical ~odel also indicates that the maximum
surface wind produced by a ramp-shaped mountain is about
50%greater than the cor-responding maximum for the
isolated.symmetrical mountain.
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c.Observations at Boulder,Colorado indicate that the
point of wind speed maximum shifts up and dow»the
slopes and out into the plains to the east.)Highest
speeds occur when the maximum is located at the foot of
the mountains.With the surface wind maximum at the
foot of the mountain,wind speeds recorded upstream on
/
the lee slope of the mountain,the downstream about 10
km east on the plains,were 50%less t~an speeds in the
area of maximum velocity.Wind velocities in the
mountains can be very low during wind storms over the
foothills and adjacent plains.
Topographic features indicating low wind speeds include:
1.Areas of high surface rougnness,forested areas or hilly
terrain will both inhibit wind flow,forested hilly
terrain having a maxim~m retarding effect on the wind.
2.Sheltered basins.
3.Valleys and canyons which are short,or perpendicular to the
prevailing winds aloft.
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REFERENCES
1.Klemp,J.B.and O.K.Lilly,"Numerical Simulation of
Hydrostatic Mountain Waves",Journal of the Atmospheric
Sciences,Vol.35 (Jan.78)pp.78-107.
2.Sangster,wayne E.,An Updated aDjective Forecast Technique
for Colorado Downslope Winds,U.S.Dept.of Commerce,NOAA
Technical Memorandum NWS CR-61,Kansas City,March 1977.
3.Br~nkman,W.A.R.,"Strong Downslope Winds at Boulder,
Colorado",Monthly Weather Review,Vol.102 (Aug.74)
pp.592-601.
4.Klemp,J.B.and D.K.Lilly,"The Oynamics of Wave-Induced
Downslope Winds",Journal of the Atmospheric Sciences,
Vol.32 (Feb.75)pp.320-339.
5.Simiu,Emil,and James J.Filliben,Statistic)l Analysis of
Extreme Winds,U.S.Department of Commerce,National
Bureau of Standards,Washington,D.C.,June 1975.
6.Slmiu,Emil and Robert H.Scanlan,Wind Effects on
Structures,John Wiley &Sons,New York
7.Sachs,Peter,Wind Forces in Engineering,Second Edition,
Pergamon Press,Oxford 1978,p.41.
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APPENDIX 1
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APPENDIX 1
VARIABLE LIST
The following variables from the NEWF4 were read into the SPSS
\program.
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Year -
MTH -
DAY -
TIME -
FAI -
BIG -
GKN -
VDZ -
ANC-
UD -
US -
UP -
UA -
ASP -
ASH -
AST -
ASRH -
ASD -
ASS -
A7p -
A7H -
A7T -
A7RH -
A7D -
A7S -
ASP -
ABH -
A8T -
ABRH -
Calender year of observation (81 in all cases)
Month of observation (1 =January,2 =February,3 =
March)
Day of the month of observation
Alaska Standard Time of observation
Fairbanks surface pressure
Big Delta surface pressure
Gulkana surface pressure
Valde~surface pressure
Anchorage surface pressure
Summit Wind Direction
Summit average wind speed
Summit peak gust wind ~)eed
Summit altimeter setting (inches mercury)
Anchorage 500 mb pressure (always 500 mb.)
Anchorage height of 500 mb surface (meters)
Anchorage 500 mb temperature (-C)
Anchorage 500 mb relative humidity (percent)
Anchorage wind direction at 500 m~(degrees true)
Anchorage wind speed at 500 mb (meter/sec)
Anchorage 700 mb pressure (always 700 mb)
Anchorage height of 100 mb surface (meters)
Anchorage 700 mb temperature (-C)
Anchorage 700 mb relative humidity (percent)
Anchorage wind direction at 700 mb (-true)
Anchorage wind speed at 700 mb (meter/second)
Anchorage 850 mb pressure (always 8S0 mb)
Anchorage height of 850 mb surface
Anchorage 850 mb temperature (-C)
Anchorage 850 mb relative humidity (percent)
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ABO -
ABS -
FSP -
FSH -
PST -
F5RH -
PSO -
FSS -
F7P -
F7H -
F7T -
F7RH -
F7D -
F7S -
PBP -
rap -
PBT -
FBRH -
FBo -
PBS -
A7 -
VARIABLE LIST
(Continued)
Anchorage wind direction at 850 mb (-T)
Anchorage wind speed at 850 mb (mete~/record)
Fairbanks 500 mb pressure (always SOD rob)
Fairbanks 500 mb height (meters)
Fairbanks 500 mb t~mperture (·C)
Fairbanks 500 mb relative humidity (percent)
Fairbanks 500 mb wind direction (-true)
Fairbanks 500 rob wind speed (meters/second)
Fairbanks 700 rob pressure (always 700 mb)
Fairbanks 700 mb height (meters)
Fairbanks 700 rob temperature (·C)
Fairbanks 700 relative humidity (percent)
Fairbanks 700 wind direction (-true)
Fairbanks 700 wind speed (meters/record)
Fairbanks 850 mb pressure (always 850 mb)
Fairbanks 850 rob height (meters)
Fairbanks 850 mb temperature (-C)
Fairbanks 850 mb relative humidity (percent)
Fairbanks 850 mb wind direction (-true)
Fairbanks 850 rob wind speed (meters/second)
Sensor 7 average wind speed (MPH-128 second averaging
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period)
AVGDIR7 -Sensor 7 direction of average wind speed (-T)
P7 -Sensor 7 peak wind speed (instantaneous measurement)
PKDIR7 -Sensor 7 direction of peak wind speed (-T)
AS -Sensor e average wind speed (MPH-128 second averaging
period)
AVGDIR8 -Sensor 8 direction of average wind speed (-T)
pe -Sensor 8 peak wind speed (MPH-instantaneous
measurement)
PKDIR8 -Sensor 8 direction of peak wind speed (-T)
,n
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VARIABLE LIST
(Continued)
rneasure-
( •T)of average wind speed
speed (MPH-instanteous
I\VGDR15 L
P15 -
Sensor 15 average wind speed (MPH-128 second averaging
period)
Sensor 15 direction
Sensor 15 peak wind
ment)
PKOIR15 -Sensor 15 direction of peak wird speed (-T)
1\15 -
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(Note:The 6 most stable layers between 900 and 500 MB at
Anchorage and at Fairbanks have variable names of the form AXXXn
where XXX is the name of the parameter and n is the number of
the level.
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APn -
FPn -
AHn -
FHn -
ATKn -
FTKn -
ALRn -
FLRn -
ADIRn -
F01Rn -
ASPn -
FSPn -
Anchorage pressure (mb)
Fairban~~presure (rob)
Anchorage height (meters)
Fairbanks height (meters)
Anchorage layer thickness (from the nth layer to the
n +I layer)
Fairbanks layer thicknp.ss (from the nth layer to the
n +I layer)
Anchorage temperature lapse rate (·C per meter,
between nand n +1 layers)
Fairbanks temperature lapse rate (-C per meter,be-
tween nand n +I layers)
Anchorage wind direction (e T)
Fairbanks wind dire=tion (e T)
Anchorage wind speed (meter/second)
Fairbanks wind speed (meter/second)
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limit of 1 characters in a variable name for SPSS.
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VARIABLE LIST
(Continued)
The following variables were calculated within the SPSS program.•
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UMM -
AF -
FB -
FG -
FU -
Summit surface pressure (rob-calculated from UA)
Anchorage surface pressure -Fairbanks surface
pressure
Fairbanks surface pressure -Big Delta surface
pressure
Fairbanks surface pressure -Gulkana surface pressure
Fairbanks surface pressure -Summit surface pressure
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The 2 most stable layers of the atmosphere in the Healy vicinity
were estimated from the Fairbanks 6 most stable layers,unless
the Fairbanks wind direction (at those layers)was between 130
degrees and 270 degrees,in which case the Anchorage most stable
layers were used.The variables were named as follows,with n •
1,2.
SPo -
5Hn -
STKn -
STn -
SRHn -
SLRn -
SSPn -
Pressure of nth most stable layer (mbs)
Height of nth most stable layer (meters)
Thickness of nth most stable layer (meters)
Relative humidity of nth ,nost stable layer (percent)
Relative humidity of nth most stable layer (percent)
Temperature lapse rate of nth most stable layer (·C
per meter)
Wind speed of nth most stable layer (meter/second)
Also computed were:
A5x -Anchorage x component of 500 mb wind velocity (m/s)
A5y -Anchorage y component of 500 mb wind velocity (m/s)
A7x -Anchorage x component of 700 mb wind velocity (m/s)
A7'j -Anchorage y component of 700 mb wind velocity (m/s)
_A1_
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VARIABLE LIST
(Continued)
A8x -Anchorage x component of 850 mb wind velocity (m/s)
A8y -Anchorage y component of 850 mb Ioiind velocity (m/s)
F5x -Fairbanks x component of 500 mb wind velocity (m/s)
F5y -Fairbanks y component of 500 mb wind velocity (m/s)
F7x -Fairbanks x component of 700 mb wlnd velocity (m/s)
F7y -Fairbanks y component of 700 mb wind velocity (m/s)
F8x -Fairbanks x component of 850 mb wind velocity (m/sl
F8y -Fairbanks y component of 850 mb wind velocity (m/s)
ATS8 =Anchorage 500 mb temperature-Anchorage 800 mb temperature
AT57 =Anchorage 500 mb temperature-Anchorage 700 mb temperature
AT78 ·Anchorage 700 mb temperature-Anchorage 800 mb temperature
FT58 =Fairbanks 500 mb temperature-Fairbanks 800 mb temperature
FT57 =Fairbanks 500 mb temperature-Fairbanks 700 mb temperature
FT78 =Fairbanks 700 mb temperature-Fairbanks 800 mb temperature
DEL5T Anchorage 500 mb temperature-Fairbanks 500 mb temperature
['IEL7T Anchorage 700 mb temperature-Fairbanks 700 mb temperaturt!
DEL8T Anchorage 850 mb temperature-Fairbanks 850 mb temperature
After inspecting the scattergrams of various variables to determine
their range during high wind even:s,the following binary variables
were set to 1,and reset to 0 when the controlling variable of each
binary predictor was outside the range during which high winds
occurred:
FGBP =a when FG >2
BPI •a when DEL5T >5 or OEL5T <-)
BP2 =0 when DIP8 >550r DIF8 <-)
BP)•a when A8H >1410 or A8H <1150
-42-
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BPS
I BP6
BP7
I BPB
BP9
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VARIABLE LIST
(Continued)
=0 when ASS >5460
0 when STK2 >2BO.0 when F5x <-13
=0 when DIPS >50.0 when DELaT >0
0 when DEr..7T >1
-43-
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APPENDIX 2
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Meteorological Hindca~t
Study for Alaska Power
Authority Anchorage
Fairbanks Intertie Project
prepared
for
Commonwealth Associates,Inc .
by
Northern Technical Services
October 2,1980
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Introduction
In preparing this report,Northern Technical Services (NORTEC)
assumed that the transmission line route would generally follow
the Susitna River,Parks Highway,Alaska Railroad and Nenana River
from Willow to Healy.Along this route records usable for statis-
tical purposes were available at Healy,Summit and Talkeetna.
Estimates of various parameters were prepared for those locations.
In addition,estimates for Anchorage and Fairbanks were prepared
since their records aLe by far the most extensive for any point on
or near the proposed route.Small amounts of data in summarized
form were available from Clear,McKinley Park,Nenana and Willow.
Although this data was not usable for statiotical analysis,it is
presented in Tabl:26.
Topography of t~e Route
At an elevation of 220 feet,Willow lies in the broad Susitna
River Valley.From Willow northward to approximately Talkeetna,
the route is within a wide valley,although to the east the
foothills of the Talkeetna Mountains are less than five miles
distant.Temperat~res here have a much greater range than at
Anchorage,as the area is well away from the moderating influence
of Cook Inlet.Otherwise the topography has little effect.
Just north of Talkeetna,curving in an arc through south central
Alaska,the Alaska Range is oriented east-west as it passes just
south of Healy.Immediately south of Healy,mountain peaks are on
the order of 5,000 to 6,000 feet.But many Alaska Range peaks are
over 10,000 feet,while the portion of the range known as Mt.
McKinley reaches 20,000 feet.The Alaska Range forms a barrier to
the low-level movement of air.But under certain barometric
conditions,wind is funneled through openings in this barrier at a
much greater speed than would occur over flat terrain.Strong
northerly winds can be expected when a large high pressure center
is located over the Fairbanks area,and a low p~essure center is
Sources of Transmission Line Icing
over the Anchorage ~rea.Strong southerly winds are present with
just the reverse of the pressure patterns.
There are three sources of transmission line icing·:(a)wet
snow,(b)in-cloud icing,and (c)freezing precipitation •
The second source of trandmission line icing is in-cloud
icing.The mechanism of transmission line in-cloud icing is
similar to that of aircraft icing,and occurrs when clouds or
Other than blowing spray for structures on or near bodies of
water.
•
Because no known wind speed records exist for the remainder of
the Nenana River ~anyon,we recommend that equipment for addi-
tional wind speed measurements be installed at Moody,Carlo,
Windy,Garner and Hurricane,Alaska (See Figure 1 foldout).
The Nenana River Canyon from Windy to Healy is the main wind
funnel for a lOO-mile stretch of the Alaska Range.The canyon
drops from an elevation of 2,OUO feet near Windy to 1,300 feet at
Healy,forming a 30-mile-Iong wind funnel bringing southeasterly
chinook winds to Healy.Conseqcently,Healy has recorded the
greatest wind speeds of any location along the proposed route for
which records are available.A detailed discussion of data and
wind damage at Healy will be found later in this report •
Wet snow accretes on electric wires in significnnt quantities
when the air temperature is between 30-F and 36-F and the rate of
snowfall is .15 inches per hour or more.1 Although such condi-
tions are common at Valdez and other places on Prince William
Sound,they occur rarely,if ever on the proposed Anchorage-
Fairbanks route.Therefore,accretion of wet snow was not inves-
tigated in this study.
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ground fog deposit an ice coating on an exposed surface.Signifi-
cant in-cloud icing may occur when the temperature is between 32-F
and 23·F.In order to estimate the amount of in-cloud icing,
upper air data including temperature lapse rates and water content
are required.2 Along the proposed route,this data is available
only for Anchorage and Fairbanks,and only from the National
Climatic Center,Ashville,N.C.Since conversations with engi-
neers at Golden Valley Electric Association,Matanuska Valley
Electric Association and Chugach Electric Association indicated
that in-cloud icing is not significant in the area of the proposed
line,and to avoid delay,in-cloud icing was not addressed in this
report.
Ice Density
The ice density depends on the type of icing.Three types
occur:3
Glaze is hard,highly adhesive,usually clear and has a
density of about .9 gm per cm 3 •Freezing precipita-
tion always deposits glaze,as may in-cloud icing under
certain conditions.
Rime,sometimes referred to as hard rime,contains air
bubbles giving it an opaque appearance,moderate adhe-
siveness and a den3ity of .3 to .8 gm per cm 3 •
In-cloud (fog)icing usually deposits rime.
Hoar frost,sometimes called soft rime,is a frost-like
deposit from frost on in-cloud icing that has low adhe-
sive qualities and a density of less than .6 gm p~r
cm 3 •
Figure 2 (after Kuroima)shows the wind and temperature condi-
tions producing each type of in-cloud icing.4
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Relation Between Icing Type and Meteo~olo9ical Condi-
tions
SO'T IlIIoIE
HAIID ItllllE
,
GI.UE ,-,,,,,,,,,,,,,,
•,••",;".~.-'--"-'-~~-~,~~~~~.~!;--~~~-'-:;!."
u•
S "
>•~_.•
•>
~
i ,
FIGURE 2.
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Method of Estimation
The estimates of extreme wind speed and estimates of extreme
temperatures presented in this report were calculated according to
the procedure specified by Irving Gringorten in his paper
"Extreme-Value Statistics in Meteorology-A Method of
Application".5
In order to estimate the maximum wind speeds likely to occur
during icing events,hourly records were searched,and maximu~1
wind speeds were recorded for the period applicable to each
freezing precipitation event.The applicable period was d~fined
as beginning at the start of the freezing precipitation and end
either 24 hours after the end of the freezing precipitation,or
when the temperature rose to 34·F,whichever occurred first.
Annual maximums of wind speeds occurring with freezing precipita-
tion were then determined,and extreme speed estimates were then
made according to Gringorten's method.
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Confidence Level of the Estimates
Except for Healy wind speeds,all estimates in this report
are at the 99 percent confidence level.Therefore,we can expect
that there is only a one-percent chance of the extreme value being
exceeded,provided that the extremes of the parameter in question
are truly double-exponentially distributed,and that the sample
mean and standard deviation are identical to the mean and standard
deviation of the extreme value population.For Anchorage and
Fairbanks,we assume that the sample and population statistics are
very close to each other,because the period of record is ade-
quately long.At Summit and Talkeetna,the period of record is
considerably shorter,and,therefore,less confidence can be
assumed for the m~an and standard deviation of those populations.
At Healy,the period of record was too short to calculate esti-
mates with 99 percent confidence.Therefore,95 percent
confidence estimates were used.However,it is not reasonable to
assume that the mean and standard deviation of our small sample
(about 2.5 years)are truly the mean and standard deviation of the
population of extreme wind speeds at Healy.Furthermore it is
possible that,because of its special topography,the extreme wind
speeds at Healy are not actually double-exponentially distributed.
During the 2.5 years of record at Healy,maximum wind speed
records include two 61 MPH events,as well as severol events in
the 50-59 MPH range.Subjectively,then,the estimates such as a
114 MPH 1 minute average wind at the 32.8 foot (10 meter)level
seem reasonable.
Application of the Estimates
All of the estimates of extreme wind speeds are for a 1
minute average wind speed at a height of 32.8 fe~t (10 meters)
above the surface.The following formula is generally accepted
for finding the wind speed at other heights near the surface:6
Maximum gust wind speeds will be greater than the 1 minute
average speed.The following formula may be used to calculate the
maximum instantaneous gust speed:?
For all return periods at Healy the extreme wind estimates
are for over 110 MPH.Estimates are based on a 2.4 year period
of record at Healy,during which speeds of over 70 MPH were
recorded.The speeds are,however,the power plants operator's
hourly entry into his log,and it is possible that higher speeds
did occur between these observations.Furthermore,by examining
Figure 3,a map cf the Healy area,we note that other locations in
the area probably experience higher extreme wind speeds than the
Healy power plant,where the record observations were made.The
power pant is at the mouth of the Healy River Canyon,but is
approximately 2 miles east of the air streamline for winds from
the Nenana River Gorge.It seems likely that the greatest wind
speeds in the Healy area occur closer to the air streamline
centerline as orographic constrictions such as the Healy River
Gorge.The strongest winds along the Nenana River Gorge from
windy to Healy probably do occur close to Healy,and are the
result of temperature-gradient drainage (chinook)forces being
added to large-scale pressure gradient forces.Therefor~,the
areas of maximum wind speed are at the bottom of the canyon.
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1/7
V,:v(,;.)
G =1.29V +5.8
Extreme Winds at Healy
v •speed at 32.8 feet
Z =height above surface in feet
Vx 2 speed at height Z
V a average wind speed (MPH)
G a maximum instantaneous gust speed
(MPH)
Figure 3.
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.....
.•...,::..
".
POINTS OF WIND DAMAGE
CD TRANSMISSION TOWER .q70 @ TRANSMISSION TOWER 484
@ TRANSMISSION TowER 411 @ RAILR(lAD ROUNDHOUSE
@ HEALY POWER PLANT @ HIGHWAY CONSTRUCTION
CAMP
MAP OF
ALASKA
"
"-'
HEALY,
AREA
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Wind Damage at Healy
On December 13,1967,a wind storm blew down Towers 470 and
471 of an existin~Healy to Fairbanks transmission line (See
Figure 3).Tower 484 was damaged,as wpre the Healy Power Plant
walls and roof,and the Alaska Railroad Roundhouse.At a highway
construction camp,closer to the mouth of the Heal}River Canyon
than the power plant,one building was destroyed and a G,OOn
gallon fuel tank (half-filled)was overturned and rolled down-
hill.
The Stanley Engineering Co~pany report estimated the wind
direction at "between 15 and 19 degrees from the longitudinal".8
Stanley Engineeri~g calculated the minimum wind speed for.these
failures to be 106 MPH for a longitudinal wind and 100 MPH for a
quartering wind.However,the two towers blown down did not fail
in the manner indicated by these calculations.Therefore,Stanley
Engineering concluded that the failures were not caused by static
wind loading,but rather due to dynamic loading caused by wind
gusts.Consequently,it is not possible to infer the wind speed
experienced during this event from the steady-state wind speed
required to cause failure.However,the failure does seem to
confirm the design study's conclusion that "wind load3 of any
consequence on the line will be caused by turbulent high velocity
gusts of short duration rather than by steady winds".9
Recommendations at Healy
If the cransmission line is to connect the existing Healy
Power Plant this area of extreme winds cannot be avoided.There-
fore,NORTEC recommends installation of equipment measuring wind
speeds at severai locations in the Healy area in order to deter-
mine design winds and the least hazardous route.
o ·.076
So ••081
Vg=39.15
Sv'8.32
Data Base:11 1/2 years (1969-1980)
Anchorage Estimated Extreme One ~inute Average Wind
Speed for Various Return Periods (99$confidenc~)
Period Accumulation
(Yes)Cinches)Standard Deviation
25 .542 • 1 62
50 .591 • 1 70
100 .627 .178
Period Speed
(Yrs)(MPH)Standard Deviation
25 87.0 9.2
50 92.0 :0.0
100 95.7 10.8
,
Data Base:27 years annual ~xtreme winds (1953-1979)
TABLE 2 Anchorage Freezing Precipitation Estimated Annual
Extreme of Accumulation on a Horizontal Surface (99%
confidence)
TABLE 1
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----------
Data Base:11.5 y~ars surface observations (January,1969 -May,1980)
JunMayAprMar<80JanDecOctSep
Anchorage Mean Monthly Incidence of Freezing Precipitation
Aug
These statistically-based temperature estimates do not take into
account the heat-absorbing capacity of the water surrounding
Anchorage and may,therefore,be somewhat higher than practical
experience would indicate.
Period Maximum"Standard Minimum Sta -,-<d
(Yrs)( •f·)Deviation ( •F)Dev;-~!...-
25 97.1 3.6 -54.9
50 99.0 4.3 -58.4 I.-
lOa 100.5 4.6 -61.9 8.2
Jul
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Maximum extreme temperature:T.78.19 e F ,ST =3.28
Minimum extreme temperature:T =-21.41 -F,ST =5.87
Data Base:27 years annual extreme temperature
TABLE 4 Anchorage Estimated Extreme Temperature (99%co~=idence)
TABLE 3
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B.20
7.S3
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l-s =9.80 s :10.1
t-s =S.30
.86 .76 ..83 (.08)
I s:1.76 ,=175 s=13&.S :.29 ,.."
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Data Base:11 years (19b9-1979)
V =12.55,S =3.45
Period Speed
(Yrs)(MPH)Standard Deviation
25 32.4 6.6
50 34.4 7.2
100 36.0 7.9
IS-I'?20 24 '25 29 30·34 35-39 40-44 ~45
MAXIMUM WIND SPEED -MPH
CATA BASE 11.6 YEARS (JAN 69 -JUL SO)
10-14
IIIB
'-9
Anchorage Frequency of ~aximum Wind Speeds Occurring with
Freezing ?recipitation
Anchorage Estimated Maximum Wind Speed Occurring with
Freezing Precipitation (99%confidence)
0-<
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8.33--
-
2.40
-
.67
.06 ,, ,
,,,,,, ,,- -
o
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~
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~
~
:::6
~
~5 <
X
'"4 2w•
TABLE 5
TABLE 6
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Fairbanks Freezing Precipitation,Estimated Annual
Extreme of Accumulation on a Horizontal Surface (99%
confidence)
Period Accumulation Standard
(Yrs)(inches)Deviation
25 .206 .066
50 .226 .069
100 .241 .073
Pe r iad Speed
(Yes)MPH Standard Deviation
25 70.9 7.6
50 75.0 8.3
100 78 . 1 9.0
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TABLE 7
Data Base:
TABLE B
Data Base:
Fai~oanks Estimated Extreme One Minute Average Wind Speed
for Various Return Periods (99%confidence)
31 years annual extreme winds (1949-1979)
VE =31.13
Sv =6,,91
11 1/2 years (January,1969 -July,1980)
jj =.015
So :.033
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TABLE 9 Fairban~s Mean Monthly Incidence of Freezing Precipitation
1.91
1.06 .B'1.23 (.17)
s =2.87 5 =3.78 5 =.58s=199 $=2.15
Jul Aug Sep Oct Nov Dec Jan reb Mar Apr May Jun
Dat3 Base:11 1/2 years (January,1969 -July,1980)
TABLE 10 Fairbanks Estimated Extreme Temperature (99%confidence)
Period :1aximum Standard Minimum Standard
(Yrs)( •F)Deviation (-F)Deviation,
25 108.9 4.2 -84.3 6.4
50 111 .2 5.3 -87.8 8.1
100 112.9 5.7 -91 .3 8.7
Data Base:31 years annual extreme temperatures
Maximum extreme temperature:T =87.26 -F,ST =3.77
Minimum extr~me temperature:T =-51.39 -F,ST =5.78
..
MAXIMUM WINO SP~EO -MPH
DATA BASE 11.6 'fEARS (JAN 69 -JUL eo)
v =13.0,5 =7.96
Data Base:10 years (1970-1979}
TABLE 12 rairban~s Estimated Maximum Wind Speed Occurring with
Freezing Precipitation (99%confidence)
I I
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30-34 .35-39'",,0-44 I ~45
.11 31
15-19 I 20-24 '25-29
Period Spoaed
(Yrs)(MPH)Standard Deviation
25 5B.B 15.9
50 63.5 lB.3
100 67.1 19 .9
~
lOT
<w a...,...
>
~w •~
~~17~
~4 -I-0
'"z
~2w
~.57
0 I ,I0-.5-9 10-14
TABLE 11 Fair~anks Prequency of ~aximum Wind Speeds Occurring with
Preezing Precipitation
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TABLE 13 Healy Estimated Extreme One Hinute Average Wind Speed foe
Various Return Periods (95%confidence)
Peelod Speed
(Yrs)(MPH)Standard Deviatio:.
25 1 14.4 12.2
50 118.2 13.3
100 124.9 14 . 4
Data 3ase:Montrly Maximum Nind Speeds (January,1978 -!'lay,1980)
VE =.42.2,';\1 =11.1
NOTE:P~riod at record is too short to calculate estimates with 99%
con fiden<:e.
TAJ3LE 14 Swrmit Estimated Extreme One Hinute Average Wind Speed for
Various Return Period (99%confidence)
Period Speed
(Yrs)(MPH)Standard Deviation
25 69.2 12.8
50 72 .0 14.2
100
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74.2 14 •7
Data Base:7 years annual extreme winds (1968-1975,1973 missing)
vE =42.0
Sv 4.7)
••
Period Accumulation Standard
('irs)(inches)Deviation
25 .283 •115
50 .310 •1 29
100 .331 .1 33
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TABLE 15
Data Sase:
TABLE 16
Summit freezing Precipitation,Estimated Annual Extreme of
Accu~ulation on a Horizontal Surface (99i confidence)
8 years (t968-1975)
ii =.018
So •.046
Summit ~ean ~onthly Incidence of Freezing Precipitation
Data Base:8.75 years surface observations
I~2
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I~
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LS9)1.78
.80 •••(.2l),=1.03 ,:3.79 ,=.59,=2.13 $;2.40
Jul Aug Sep Oct Nov Dec Jan reb Mar
(.14)
s:.40
Apr May Jun
TABLE 17 Summit Estimated E~treme Temperature (99%confidence)
TABLE 18 Summit Frequency of Maximum '1oJind Speeds Occurring with
Freezing Precipitation
Data Base:8 years annual extreme temperatures
Maximum extreme temperature:T s 77.63 e F ,ST Z 4.63
Minimum extreme ~emperature:T z -36.5 e F ,ST a 4.96
Period ?1aximum Standard Minimum Standard
(Yrsl (·F)Deviation ( •FI Deviation
25 104.3 11.6 -64.8 12.4
50 107.0 12.5 -67.8 14.9
100 109.1 13.0 -70.7 17.4
.13 .10 .12
1.35
t 10-14 I 15-19 20-24 25-29 30-34'35-39 I 40-44 I ;t 45
MAXIMUM WIND SPEED -MPH
DATA BASE 7.8 YEARS (JAN 69 -OCT 16)
10
'"~8~
>
'"~•..
~
'"~40
%
z I.BI•Z~
~.73
0 I0-'5-9
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TABLE 19 Summit Estimated Maximum wind Speeds Occurring with
rre~zing ?recipitation (99%confidence)
I
)
Period Speed
(Yrs)(MPH)Standard Deviation
2:68.4 25.0
,50 73.8 26.8
100 77.8 27.7
Data Base:7 years (1968-1976,except 1970,1976)
V =17.0,sv:::8.94
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i TABLE 20 Talkeetna Estimated Extreme One Minute Average Wind Speed
for Vtrious Return Periods (99%confidence)
Peelod Speed
(Yes)MPH Standard De',iat ion
25 51.5 8.0
50 53.9 8.4
100 55.7 8.8
i
j
"
1 Data Base:11 years annual extreme winds (1968-1979 inclusive,1975
missing;part-time operation 1977-1979)
VE •28.45
Sv'4.01
I
If
••
JunMayAprMarrebJanDecNovOctSep
12 years surface observations (1968-t979)
Aug
'50 =.044
D .030
Period Accumulation
('irs)(inches)Standard Deviation
25 .285 .084
50 .31 1 .088
100 .331 .092
Data Base:12 years (1968-1979;part-time 1~77-1979)
u1
TABLE 22 Tal~eetna Mean Monthly Incidence of Freezing Precipitation
TABLE 21 Talketeena Freezing Precipitation Estimated Annual Extreme
of Accumulation on a Horizontal Surface (99%confidence)
Data Base:
f-
7.0
-s :9.25 2.98
(.57)s;4.77 .73 1.351
I I I
s:1.23 s=1.08s:,35 ,
J
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TABLE 23 Talkeetna Estimated Extreme Temperature (99%confidence)
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Perlod Maximum Standard Minimum Standard
(Yrs)(oF)Deviation (ef')Deviation
25 100.9 5.2 -87.1 16.6
50 102.6 5.7 -92.4 17.5
100 103.9 6.0 -97.6 18 .4
I Data Bas~:12 years annual extreme temperatures
I Maximum extreme temperature:if =84.4 -F,ST =2.67
~inimum extreme temperature:T =-37.25 eFt ST ~8.75
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TABLE 24 Talkeetna Frequency of MaxiJmm ~iind Speeds Occurring with
Freezing Precipitation
t
15 19 20 24 25 29 30 34 ~5-39 40-44 ~4510145•o ,
8.84
f-
-f-
H.
-f-1.99
.>2 , ,,,,,I I ,,I I I I-- -----
'0
'"4 •W
~
'"w •~
~
'"~•0:
z
4 ,
W,
0
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MAXIMUM WIND SPE~D -MPH
DAH BASE 9.1 Y:'AAS (l DEC 68 -31 DEC 77)
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TABLE 25 Talk~etna Estimated Maximum Wind Speeds Occurring with
Freezing Precipitation (99%confidence)
Period Speed
(Yrs)(MPH)Standard Deviation
25 32.8 7.3
50 35.1 B.O
100 36.8 8.8
Data Base:11 years (1968-1979,except 1974)
~~10.82,Sv =3.82
,.
[TABLE 26 Climate of Locations Without Estimates
f
For some stations along the proposed rout~,the data avail-
able was not usable for statistical purposes.However,it may
still be of some interest,and is tabulated below.
Eielson Air Force Base (Fairbanks):
Extreme Wind Speed 69 MPH (1 min average,SW)
Record High Temperature ;~·F
Record Low Temperature -62·F
Period of Record 4.5 years (1944-1951,
incomplete)
Record does not indicate if this is a 1 minute average of a
gust.
Ladd Air Force Base (Fairbanks):
Clear:
Extreme Wind Speed
Record High Temperature
Record Low Temperature
Period of Record
70 MPH (Southwest)·
92"P
-62·F
5 ye3rs (1946-1967,incomplete)
not available
96·F
-62"P
8 years (1966-1974/part-time)
(Ancho~age)
93 MPH (peak gust,1 minute
average not available,north)
not available
15 years (1946-1967,incomplete)
High Temperatures
of Record
Record
Period
Extreme Wind Speed
Record High Temperature
Record Low Temperature
Period of Record
Elmendorf Air Force Base
Extreme Wind Speed
•
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I,
!1cKinley Park:
Extreme Wind Speed
Record High Temperature
Record Low Temperature
Period of Record
Nenana:
Extreme Wind Speed
Record High Temperature
Record Low Temperature
Period of Record
Wasilla:
Extreme Win~Speed
Record High Temperature
Record Low Temperature
Period of Record
Willow:
Extreme Wind Speed
Record High Temperature
Record Low Temperature
Period of Record
not available
89-P
-54-F
53 years (1922-1975/part-time)
not availahle
98'r
-69-P
46 years (1922-1968)
not available
90·P
-38'r
24 years (1951-1975/part-time)
not available
90'r
-56-F
13 years (1963-1976,part-time)
.1
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t
Source of Data
Golden Valley Electric Association,Inc.
Box 1249
Fairbanks,Alaska 99707
National Climatic Center
Federal Building
Asheville,North Carolina 28801
University of Alaska
Arct.ic Environmental Information and Data Center
(Repository for National Cl~matic Center records within Alaska).
707 A Street
Anchorage,Alaska 99501
•
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References
.1
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1.Wakahama,Gerow,Kuroiwa,n4isuke and Gato,Kazuo,·Snowfall
hccretion on Electric Wires and Its Accretion-,Journal of
Glaciology,Vol.19,No.81,1977.
2.Chaine,P.M.,In-Cloud Icing -Industrial Meteorology Study
y,Information Canada,Ottawa K1AOS9,1974.
3.McKay,G.A.and Thompson,H.A.,-Estimating the Hazard of
Ice Accretion in Canada from Climatological Data-,Journal of
Applied Meteorology,December,1969,pp.927-935.
4.Kuroiwa,Dai~uke,Icing and Snow Accretion on Electric Wires,
u.s.Army Cold Regions Research and Engineering Laboratory,
Research Report 123,Hanover,N.H.,January,1965.
s.Gringorten,Irving t.,Extreme-Value Statistics in
Meteorology - A Method of Application,Air Force Cambridge
Research Center,June,1960.
6.Haltiner,George J.and Martin,Frank L.,Dynamical and
Physical Meteorology,p.232.McGraw Hill Book Company,New
York,1957.
7.Boyd,R.W.,Climatic Information for Building Design in
j Canada,National Building Code of Canada,National Research
Council of Canada,NRC No.11153.
J 8.Stanley Engin~ering Company,Wind Damage Study -Healy Power
Plant {for Golder Valley Electric Association}Muscatine,
Iowa,1968.
9.Stanley Engineering Company,Report on Selection of
Structures for 138kv Transmission Line {for Golden Valley
Electric Association}Muscatine,Iowa.
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APPENDIX 3
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NORTHERN TECHNICAL SE'lYICES
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ISOTACH ANALYSIS
T£CHNICAL SEA'JICESNORTHERN.-~~.....UT"".
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A..ASKA POWER AUTHORI'TV
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