National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Conference Paper 

NREL/CP-500-38109 

May 2005 

Towards a Wind Energy 

Climatology at Advanced 

Turbine Hub-Heights 

Preprint 

Marc Schwartz and Dennis Elliott 

To be presented at the American Meteorological Society’s 

15th Conference on Applied Climatology 

Savannah, Georgia 

June 20–23, 2005 
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1

JP1.9 TOWARDS A WIND ENERGY CLIMATOLOGY AT ADVANCED TURBINE 

HUB HEIGHTS

Marc Schwartz and Dennis Elliott 

National Renewable Energy Laboratory, Golden, Colorado

1. BACKGROUND

The size and rated capacity of commercial wind 

turbines have grown steadily since the early 

1990s. Typical turbines in the 1990s were rated 

below 1 MW, with rotor diameters of around 30–50 

m and hub heights 40–60 m. Recent technological 

advances in wind turbine design have increased 

the generation capacity above 1 MW and raised 

the hub height of the machines used in new wind 

farm projects to around 80 m above ground level. 

The trend of larger turbines will continue; some 

turbines currently under development for 

deployment during the second half of this decade 

are rated at 2–5 MW of energy generation with 

rotor diameters near 100 m and hub heights of 

100–120 m. These advanced turbines will take 

advantage of the higher wind speeds aloft to 

generate more wind energy. Specific knowledge of 

important wind characteristics at turbine hub 

height is still needed to optimize turbine design 

and wind farm layout. Physical measurements of 

parameters such as wind speed, wind power 

density, and wind speed shear at heights of 80–

120 m were virtually nonexistent a few years ago 

and are still rare today. 

Most wind energy anemometer measurements are 

at heights of 50 m or lower. A common practice in 

the wind energy industry is to analyze data from 

the shorter towers and extrapolate these data to 

turbine hub heights for wind farm design and wind 

energy prediction. This technique is much less 

reliable for hub heights of 80 m and higher. The 

decreasing influence of surface roughness on 

wind shear and increasing influence of lower 

atmospheric features such as low-level jets and 

thermal circulations makes simple extrapolation 

prone to large errors. Recently updated state wind 

resource maps (Schwartz and Elliott 2004) are 

used for regional wind farm siting. However, the 

maps are only validated for 50 m above the 

ground and the resource patterns depicted on the 

maps may not accurately reflect the distribution of 

the resource for levels 80 m and higher. 

_______________________

*Corresponding author address: Marc Schwartz, 

National Renewable Energy Laboratory, Golden, CO 

80401; e-mail: marc_schwartz@nrel.gov 

The wind energy community has recognized the 

need to fill the data gap. Programs instituted at the 

state level and, in large part, supported by the 

U.S. Department of Energy (DOE) place 

anemometers and vanes at several levels on 

existing tall (80 m+) communication towers. The 

wind resource group at DOE’s National 

Renewable Energy Laboratory (NREL) has 

obtained many of these measurement data. We 

have begun to analyze important wind climate 

parameters such as wind speed, power, and shear 

from the tall towers. The distribution of the tall 

towers varies among the states that participate in 

the program, because the tall tower program is 

new and the available funding to establish tall 

towers is variable. Tall tower data from Kansas, 

Indiana, and Minnesota (which have the greatest 

number of tall towers with measurement data) will 

be the focus of this paper. Analyses of data from 

the tall towers will start the process of developing 

a comprehensive climatology for wind energy 

development areas in the United States. 

2. NEED FOR TALL TOWER CLIMATOLOGY 

Measurements of wind characteristics over a wide 

range of heights up to and above 100 m are useful 

to: (1) characterize the local and regional wind 

climate; (2) validate wind resource estimates 

derived from numerical models; and (3) evaluate 

changes in wind characteristics and wind shear 

over the area swept by the blades. Developing 

wind climatology at advanced turbine hub heights 

for the United States benefits wind energy 

development. Regions where a climatology is 

most important include the central United States 

between the Rocky Mountains and the 

Appalachians, the interior western states between 

the Pacific Ocean and the Rocky Mountains, and 

the northeastern and mid-Atlantic states. Specific 

circulations such as the nocturnal low-level jet and 

the land-sea breeze influence many locations in 

these regions. These circulations may have a 

greater influence on the wind resource at 80–100 

m than at 50 m. The strong winter winds aloft that 

frequently affect the northern and central tiers of 

the United States may also affect the wind 

resource. These winds are often prevented from 
2

mixing down to the 50-m level by a strong surfacebased stable layer, but whether or how often these 

winds descend to the 100-m level is not known. 

A tall tower wind climatology will better define 

areas in the United States where wind energy 

projects could be feasible, and may include 

regions where current 50-m measurements 

indicate the wind resource may not be sufficient 

for a profitable project. DOE supported projects 

that establish wind measurements on 

communication towers through grants from its 

State Energy Program (SEP) in fiscal years 2002 

and 2004. Figure 1 shows states that have 

established tall tower measurements from SEP 

funding and in-state programs. Three states in the 

midwestern United States—Kansas (6 towers), 

Indiana (5 towers), and Minnesota (9 towers)—

had sufficient regional distribution of these towers 

to begin an analysis of the regional wind 

climatology at advanced hub heights. 

Unfortunately, only a subset of the towers in 

Indiana and Minnesota was used in the analysis 

because of short periods of record or questionable 

data. The wind climates in these states are 

interesting because the southerly nocturnal lowlevel jet strongly influences the climates in Kansas 

and Minnesota, and Indiana is on the eastern 

edge of its area of influence.

3. TALL TOWER ANALYSIS METHODOLOGY

The raw time series of 10-minute tall tower 

observations of wind speed and direction were 

processed by NREL and converted to our 

standard graphs of important wind characteristics 

(Schwartz and Elliott 1997). These include annual, 

monthly, and diurnal averages of wind speed and 

power, frequency of wind speed, and frequency of 

speed by direction from each measurement level. 

An important goal in the analysis methodology is 

to have the best possible measurement data. We 

inspect the patterns on the graphs for possible 

periods of bad data that can slip through the initial 

quality control process performed by the 

organizations that operate these towers. For 

example, ice sometimes forms on vanes and 

anemometers, which results in long periods of low 

or calm wind speeds and unchanging wind 

directions. This causes bad data that is difficult to 

detect. The best way to detect this problem is to 

compare the monthly percentage of calm winds 

from all the measurement levels. If abnormal 

patterns occur; for example, one or more months 

have significantly more calms than others, or the 

percentage of calms increase with height, we 

Figure 1. States with tall tower measurement programs. 
3

inspect the raw time series and remove the 

suspicious data. The analysis of important wind 

characteristics can begin once we are satisfied 

that a “clean” data set is available for a particular 

station. 

Because tall tower measurement programs are in 

their infancy, the data periods of record are short, 

in some cases only one year. Short periods of 

record hinder our ability to draw definite 

conclusions about the wind climate, but 

comparisons among regional locations can still 

show important patterns. Investigations of the 

magnitudes of wind speed and wind power at 

several measurement levels, the change of these 

parameters with height, and the variation of wind 

speed by direction at the different measurement 

levels are the main analysis tools used for the tall 

tower data. 

Annual average wind speeds of 8 m/s and higher 

for heights of 80-100 m at specific locations 

generally draw interest from potential wind farm 

developers. The exact amount of wind energy 

produced at a particular site would depend on the 

distribution of the wind speeds, the turbine design, 

and the wind farm layout. Average wind speed by 

direction information for a potential wind energy 

project site plays an important role in designing a 

wind farm that minimizes turbulence and wake 

effects. Knowledge of wind shear and the 

distribution of wind speeds at a wind energy site 

are important to accurately estimate the power 

available in the wind at turbine hub height. The 

1987 “Wind Energy Resource Atlas of the United 

States” (Elliott et al. 1987), provides examples of 

wind shear and wind speed distribution values 

commonly used for wind energy calculations. In 

the atlas, extrapolation of measured wind speeds 

from low (6–10 m) towers to 50 m was based on 

the 1/7 (0.143) wind speed and 3/7 (.43) wind 

power density power law exponents for wind 

shear. The Rayleigh distribution, which 

corresponds to a Weibull k value of 2.0, often 

describes the distribution of the wind speeds at 

measurement sites in the United States and was 

used in the atlas to relate wind speed to available 

power. 

The results of the analysis of these wind 

characteristics from the three states are presented 

in Section 4. 

4. RESULTS

4.1 Kansas Results 

Six tall tower stations were established under SEP 

through the efforts of the Kansas Corporation 

Commission, Coriolis architecture-energy, and the 

Kansas Department of Transportation. The 

stations, which became operational between midApril and mid-June 2003, are broadly distributed 

throughout the western two-thirds of Kansas 

(Figure 2). The towers have anemometers and 

vanes at three levels: 50 m, 80 m, and 110 m. 

Five stations have observations through the end of 

June 2004; one has observations through early 

April 2004. The observations of wind speed and 

direction are 10-minute averages and the data 

recovery at the stations was 94%–98%. 

Figure 2. Kansas tall tower locations. 

The comparison of the wind characteristics among 

the stations provides some interesting insights into 

the regional wind climatology. The average 110-m 

wind speeds at the six sites were 8.4–9.4 m/s 

(Sumner had the lowest and Ellsworth the highest 

average speed), a level of resource that would 

draw interest from potential wind farm developers. 

There appears to be some influence of regional 

terrain on the resource because the two stations 

with the lowest resource are located in river 

valleys or drainages. 

The strong nocturnal wind speed at the 110 m 

level is an outstanding climatological feature of the 

Kansas data. The nocturnal speed peaks between 

2100 and 2400 Local Standard Time (LST) and 

the yearly average speeds at the individual towers 

are 9.5–11.1 m/s. Southerly winds are the 

prevailing direction for the year and their average 

speeds are 11.5–15 m/s at the individual towers. 

In contrast, the afternoon winds are 7.5–8.0 m/s. 
4

Therefore, most of the difference in wind resource 

at 110 m among the stations in central and 

western Kansas is due to the level of nighttime 

winds. The diurnal pattern at three of the towers 

(Figure 3) shows strong nighttime winds. 

 

The data from the Kansas tall towers show that 

the wind shear and wind speed distributions differ 

from the generalized values used in the atlas. The 

measured wind shear exponent of 50–110 m at 

the six towers was close to 0.2, which means the 

wind speed increased with height more rapidly 

than with a value of .143. The windier sites at 50 

m tended to have lower wind shears than the 

lower speed sites; however, the range of the 

speed shear exponents of 0.19– 0.23 at the six 

towers is small and does not have a major effect 

on the ranking of the towers in terms of available 

resource at 110 m. This implies that well-exposed 

50-m measurement locations in central and 

western Kansas are excellent guides to the 

available wind resource at 110 m. There is some 

differentiation between the levels of maximum 

wind shear among the towers. The wind shear at 

the 50–80-m levels was slightly greater than the 

80–110-m wind shear at the two windiest tower 

locations. At the other four stations, the 80–110-m 

wind shear was a bit greater than the 50–80-m 

shear. The wind speed distribution was similar at 

all the towers; Weibull k values at all levels were 

generally 2.3–2.5. These k values denote a 

narrower wind speed distribution than the Weibull 

k of 2.0 used as the standard in the 1987 atlas. 

There are two prevailing wind directions in this 

region: northwest and south. Data at 110 m from 

all towers indicate that strong northwesterly winds 

occur primarily during the cool season 

(September–February) and strong southerly winds 

occur all year. 

The comparative speeds between the 

northwesterly and southerly winds showed 

significant differences among the stations. The 

average speeds of the northwesterly and southerly 

winds were about the same at the two stations the 

furthest north and furthest west in the state. The 

average speeds of the southerly winds at the other 

four stations were notably stronger 1–2 m/s) than 

the northwesterly winds. Overall, the average 

speed of the northwesterly winds was 9.5–10.5 

m/s, and the average southerly wind speed was in 

the 10–12 m/s range. The two windiest stations 

(Ellsworth and Kearny) had the strongest average 

southerly winds (12.2 and 11.8 m/s respectively) 

and the largest difference between the average 

northwesterly and southerly wind speeds. 

In summary, locations with the strongest nocturnal 

southerly winds will probably have the greatest 

5

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9

10

11

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour of Day

Wind Speed (m/s)

Sumner 110 m

Logan 110 m

Kearny 110 m

Figure 3. Diurnal wind speeds at three Kansas tall towers. 
5

110-m wind resource, which emphasizes the 

importance of the strength of the low-level jet in 

central and western Kansas for controlling the 

available wind resource. There is some indication 

that the northwesterly winds in the northern and 

northwestern areas may play a primary role in 

determining the available resource in this area, but 

definite conclusions must await future 

measurements. There are plans to continue wind 

measurements at these Kansas towers for another 

one-year period. 

4.2 Indiana Results 

Five tall tower stations under SEP began 

operations in 2004 for the Indiana State Energy 

Office with the assistance of Global Energy 

Concepts, a private consulting firm in Kirkland, 

Washington. Three started measurements on 

January 1; the other two commenced in mid-April. 

The five towers are spread throughout Indiana: 

four in the central and northern parts of the state, 

and one in extreme southwestern Indiana near 

Evansville (Figure 4). 

The stations have anemometers and vanes at 

three levels: 10 m, 49 m, and 99 m (Goodland’s 

upper level is 90 m) above ground. All five stations 

recorded data through the end of 2004, and the 

wind speed data recovery exceeded 95%. 

The three stations with a full year of data are 

Goodland (in north central Indiana near the Illinois 

border), Carthage (east of Indianapolis), and 

Haubstadt (near Evansville). The comparison of 

the wind characteristics at the three stations 

shows significant differences in the wind resource 

at 90–99 m during 2004. Goodland was the only 

station to record an average wind speed high 

enough (7.7 m/s at 90 m) to encourage wind 

energy development. Carthage averaged 6.8 m/s 

at 99 m and Haubstadt averaged 6.1 m/s at 99 m. 

The two stations with more than 8 months of data 

were Geetinsville (in north-central Indiana near 

Kokomo) and La Grange (near the Michigan 

border in the northeastern part of the state). 

Extrapolating the 8-month average wind speed to 

12 months based on the patterns recorded at the 

other three stations yields average wind speeds 

around 7 m/s at 99 m at both towers. The 

predominant wind direction at the stations was 

south-southwest to southwest; winter and spring 

had the greatest resource. The most significant 

climatological feature to be analyzed was the 

higher wind resource in the north-central region 

near the Illinois border compared to other parts of 

the state. The recently updated 50-m wind 

resource map (at www.windpoweramerica.gov) for 

Indiana shows relatively high wind power in this 

region, which confirms that the 2004 wind patterns 

are not atypical. 

Figure 4. Indiana tall tower locations. 

The diurnal amplitude and pattern of wind speed 

at the upper level at the three full-year data towers 

was quite similar (Figure 5). The differences in 

wind speed among the stations were spread 

throughout the day rather than concentrated at 

night. For example, the peak nighttime wind 

speeds at Goodland averaged 8.2 m/s and the 

afternoon winds averaged 7.4 m/s. At Carthage 

the nighttime and afternoon speeds were 7.2 m/s 

and 6.6 m/s, respectively, and at Haubstadt they 

were 6.7 m/s and 5.8 m/s. The primary sources of 

the increased wind resource at Goodland were 

apparently stronger episodes of south-southwest 

winds during the winter and spring. The average 

speed of the southerly winds at Goodland was 

10.5–11.0 m/s; they averaged 8 m/s at Carthage 

and 7.5 m/s at Haubstadt. Winds from the west to 

northwest averaged 7 m/s at Carthage and 8 m/s 

at Goodland. The Weibull k values were around 

2.1 at Goodland and 2.5 at Carthage and 

Haubstadt. These data indicate a broader 

distribution of wind speeds at Goodland than at 

the other locations. 
6

The Indiana stations also exhibit wind shear 

exponents significantly greater than 0.143. The 

49–99-m (90-m at Goodland) shear was 0.23 at 

Goodland and 0.28 at Carthage. The windiest 49-

m locations tended to have less wind shear than 

the lower speed sites, though the spread of the 49 

m speeds was large enough to confirm that 

exposed 50-m speeds indicate the amount of 

available resource at advanced turbine hub 

heights. The speed shear exponent at Haubstadt 

was extreme (about 0.4). The low wind speed at 

49 m of only 4.5 m/s, about 2.2 m/s lower than the 

49 m wind speed at Goodland, may reflect 

disturbed boundary layer flow initiated by the 

undulating terrain. At the Haubstadt 99-m level the 

direct terrain influence is reduced and the average 

wind speed was only 1.7 m/s lower than the 

extrapolated 99-m speed at Goodland. 

 

Exposed sites in northwestern Indiana that are 

subject to the strong southerly and westerly winds 

could have the highest wind resource in the state. 

However, none of the tall towers were located on 

the highest terrain in their regions, so wind 

resource levels as high as Goodland could be 

measured in other areas of northern Indiana. 

Unfortunately, the five towers were 

decommissioned in April 2005, but perhaps this 

analysis will spur future public domain tall tower 

measurements across Indiana. 

4.3 Minnesota Results 

The Minnesota Department of Commerce 

established nine tall tower locations around the 

state from the mid-1990s through 2004. The 

highest level at seven of these towers is 90 m. The 

highest level at one tower is 85 m, and one other 

tower has wind data at 120 m. NREL downloaded 

wind data from these towers from the Plains 

Organization for Wind Energy ResourcesSM web 

site. Three of the tall towers had periods of record 

less than one year and were excluded from the 

analysis. Data from three other towers were 

excluded from the formal analysis after processing 

because of low data recovery levels and 

questionable data quality. The three towers used 

for the analysis (Hatfield, Marshall, and Currie) 

had anemometers at 30 m, 60 m, and 90 m and 

vanes at the 30- and 90-m levels. These towers 

are in extreme southwestern Minnesota near the 

South Dakota border (Figure 6) on the slope of a 

glacial landform called Buffalo Ridge. Buffalo 

Ridge extends from northwestern Iowa through 

southwestern Minnesota to northeastern South 

Dakota and has been a focal point of regional wind 

energy development since the early to mid-1990s. 

A regional wind characteristic resource analysis 

for southwestern Minnesota was not possible 

because the three stations are too close together. 

However, wind characteristic variations (if any) 

Figure 5. Diurnal wind speeds at three Indiana tall towers. 

5

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8

9

10

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour of Day

Wind Speed (m/s)

Haubstadt 99 m

Carthage 99 m

Goodland 90 m
7

Figure 6. Southwestern Minnesota tall tower 

locations. 

across Buffalo Ridge could be studied because 

Hatfield is on the southwestern slope and Marshall 

and Currie are on the northeastern slope. 

The years 2001 and 2002 were chosen for the 

analysis because of good data recovery at the 

three sites–about 90% at Marshall and about 95% 

at Hatfield and Currie. The 90-m speeds at the 

three towers confirm that the Buffalo Ridge area is 

suitable for wind energy development, but the data 

showed a significant difference in average wind 

speeds between Hatfield on the southwestern 

slope and Marshall and Currie on the northeastern 

slope (Figure 7). The 90-m speeds at Marshall and 

Currie were about 8.3 m/s; Hatfield recorded an 

average speed of 7.8 m/s. Most of the difference 

in wind speeds occurred at night. The peak 

nighttime speeds that occur between 2300 and 

0300 LST averaged 8.8 m/s on the northeastern 

slope, but only 8.1 m/s on the southwestern slope. 

The afternoon wind speeds were 7.6–7.8 m/s. The 

wind speed shear exponents of 60–90 m were at 

or slightly above 0.2 at the three towers. Marshall 

and Currie, the higher wind speed sites at 60 m, 

recorded lower wind shear exponent values than 

the 0.25 recorded at Hatfield. 

Analysis of wind direction data was difficult 

because of some erroneous data recorded at 

Currie and Hatfield. Marshall’s wind direction 

appeared correct at both 30 m and 90 m as it 

matched the prevailing directions recorded at 

Worthington, Pipestone, and Marshall airports 

from 2001 through 2002. The prevailing directions 

at Marshall are south-southwest and northwest. At 

90 m the southerly winds average just over 11 m/s 

and the northwesterly winds average just over 8.5 

m/s. The strong southerly winds occurred 

throughout the year and the strong northwesterly 

winds were concentrated from late autumn 

through early spring. The 90-m southerly winds at 

Currie were estimated at just over 10.5 m/s and 

the northwesterly winds around 8.5 m/s, close to 

the averages observed at Marshall. The 90-m 

direction data at Hatfield were corrupted but the 

30-m data showed the southerly winds averaged 

7.2 m/s, about 1.2–1.5 m/s lower than the 30 m 

southerly wind speeds at Currie and Marshall. The 

extrapolated 90-m southerly wind speed at 

Hatfield is around 10 m/s, which is 0.5–1.0 m/s 

lower than Currie and Marshall. 

The analysis revealed some subregional 

differences in the wind characteristics on Buffalo 

Ridge. The 90-m average wind speed at stations 

on the northeastern (downslope) side was 0.5 m/s 

higher than that at Hatfield on the upslope side of 

the ridge. The difference in average speeds is 

caused by stronger nighttime and southerly winds 

at Marshall and Currie. The results imply that 

subregional terrain can cause a significant 

difference in the wind resource. The Minnesota 

Department of Commerce continues to collect 

data at five of the tall tower locations. 

5. CONCLUSIONS 

NREL has started to analyze the wind climatology 

at advanced turbine hub heights based on data 

measured on existing tall towers in Kansas, 

Indiana, and Minnesota. The highest 

measurement level at these towers was 90–110 

m. There are two significant findings from the 

analysis: (1) the difference in wind resource at tall 

tower sites in the central United States seems to 

be controlled by the strength of the nocturnal and 

southerly winds; and (2) the average wind shear 

exponent of 50–100 m at tall towers in the central 

United States is influenced by strong southerly 

winds and is significantly higher than the 0.143 

often used for conservative estimates of the wind 

resource at turbine hub height. A common range 

of shear exponents at well-exposed sites is 

apparently 0.2–0.23; the windiest sites have 

slightly lower shear exponents (0.18–0.20). This 

finding may prove beneficial to wind energy 
8

development in the Midwest. If the shear exponent 

values above 0.2 are widespread, the wind speed 

of 100 m for many locations could be up to 0.5 m/s 

higher than previously estimated, which would 

make more locations attractive for development. 

Tall tower programs are being implemented in 

Ohio, Iowa, Missouri, South Dakota, Virginia, and 

North Carolina. Tall tower data are also being 

collected in California, Texas, North Dakota, and 

New York. In time, tall tower data supplemented 

by data from remote sensing networks may help 

us develop a clearer picture of wind characteristics 

at advanced turbine hub heights across the United 

States and allow for a more systematic 

deployment of wind farm power plants to meet our 

energy needs. 

6. ACKNOWLEDGMENTS 

We would like to thank George Scott, Steve 

Haymes, Donna Heimiller, and Ray George of the 

NREL wind resource assessment group for their 

help with this project. This paper was written at 

NREL in support of DOE under contract number 

DE-AC36-98-GO10337. 

7. REFERENCES 

Elliott, D.L., C.G. Holliday, W.R. Barchet, H.P. 

Foote, and W.F. Sandusky, 1987: Wind Energy 

Resource Atlas of the United States. DOE/CH 

10093-4. Golden, CO: Solar Energy Research 

Institute, 210 pp. 

Schwartz, M.N. and D.L. Elliott, 1997: The 

Integration of Climatic Data Sets for Wind 

Resource Assessment. NREL/CP-440-23157. 

Golden, CO: NREL 5 pp. 

Schwartz, M.N. and D.L. Elliott, 2004: Validation of 

Updated State Wind Resource Maps for the 

United States. NREL/CP-500-36200. Golden, CO: 

NREL 5 pp. 

5

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour of Day

Wind Speed (m/s)

Currie 90 m

Hatfield 90 m

Marshall 90 m

Figure 7. Diurnal wind speeds at three Minnesota tall towers. 
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4. TITLE AND SUBTITLE

Towards A Wind Energy Climatology at Advanced Turbine 

Hub-Heights: Preprint 

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NREL/CP-500-38109 

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14. ABSTRACT (Maximum 200 Words)

Measurements of wind characteristics over a wide range of heights up to and above 100 m are useful to: (1) 

characterize the local and regional wind climate; (2) validate wind resource estimates derived from numerical models; 

and (3) evaluate changes in wind characteristics and wind shear over the area swept by the blades. Developing wind 

climatology at advanced turbine hub heights for the United States benefits wind energy development. Tall tower data 

from Kansas, Indiana, and Minnesota (which have the greatest number of tall towers with measurement data) will be 

the focus of this paper. Analyses of data from the tall towers will start the process of developing a comprehensive 

climatology. 

15. SUBJECT TERMS

climatology; wind resources; wind characteristics; wind resource measurement; tall towers 

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Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18