Wind Energy Resource Atlas of the United States


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Appendix B Wind Energy Resource Information System (WERIS)


Appendix C

Annual and Seasonal Mean Wind Speed and Power Summaries For Selected Stations in the United States and Its Territories

Wind data from 975 stations in the National Climatic Data Center (NCDC) tape set TD-1440 were analyzed to provide much of the data used to create the National Wind Energy Assessment. For these 975 stations, 1,889 separate periods of record were identified, during which anemometer location, observation, frequency, and data coding frequency were constant. In this appendix, summary information on station identification, location, and annual and seasonal mean wind speeds and wind power densities are presented for these stations and periods.(see Table C-1)

Stations are grouped alphabetically by state with postal abbreviation information on each period of record following chronologically. The NCDC station number code (WBAN) is used to uniquely identify stations with the same city name. The agency responsible for station operation is identified by the TYP code:

TYP Type of Station Making Observations
A Air Force
N Navy
W Service Weather
F FAA

Station location is given by its latitude and longitude coordinates in degrees (DD) and minutes (MM). Positive latitude is north of the equator. West longitudes are less than zero. Station elevation is given in meters above mean sea level. Station location information was largely obtained from the NCDC publication WBAN Station Numbers (NCDC 1978).

Period of record information was extracted from the National Wind Data Index (Changery 1978). Starting and ending dates, coded YY=Year, MM=Month, and DD=Day, were selected to maximize the length of record. The change in coding frequency from hourly to 3-hourly by the NCDC at the end of 1964 results in many periods ending near 641231 and starting near 650101; many periods of record for Air Force stations end at 701231 at which time the NCDC stopped digitizing Air Force data. The NCDC stopped digitizing navy data on an hourly basis after February 1972. A break in the period of record also occurs if the observation frequency at the stations changed. The OBS code indicates the number of hours per day that observations were taken at the station:

OBS Hours of Observation Per Day
A 24
B 19-23
C 12-18
D 5-11
E 4
F Less than 3
Blank Unknown

Periods of record were most often interrupted by changes in anemometer height or location. Changery's index documents these changes and gives an anemometer height and location history for each station. Anemometer height is reported here in meters above the ground. The LOC code describes the type of structure on which the anemometer was located:

LOC Anemometer Location
R Roof-Top
G Ground Mast
B Beacon Tower
U Unknown Location
E Estimated Wind, No Anemometer

A roof-top location means the anemometer was located on a mast on the roof of a building with the height of the anemometer above ground as given. There is no information on the height of the mast above the roof. A ground mast signifies that the mast, with its base on the ground, is used primarily to support the anemometer. Beacon tower locations mean that the tower is not primarily used to support the anemometer but has other functions. A few early periods of record were coded from estimated wind speeds; no anemometer was available at the site. Anemometers with unknown locations usually also are at unknown heights, which are coded as -99.9.

Annual mean wind speed, in m/s, and annual mean wind power density, in W/m2, are calculated from all available data for the period of record. Seasonal mean values are based on the following months:

Season Months Included
Winter December, January, February
Spring March, April, May
Summer June, July, August
Autumn September, October, November



FLAGS USED IN THE TABLE:

Seasonal means were calculated by weighting monthly mean values by the number of observations in the month normalized by the total number of observations in the season over the period of record. Two data quality checks were calculated for the annual and seasonal mean values. The first is the ratio of the number of valid wind speed observations to the maximum possible number of observations that could have been coded during the period of record. The second is the ratio of the number of wind power density calculations that were made using estimated values of air pressure and temperature to the total number of wind power density calculations made for the period. A code symbol, after the wind power value, indicates the status of the two data quality checks:

Code Ratio: Total Number/Maximum Possible Number Ratio: Estimated Number/Total Number
Blank 0.75 0.50
# 0.75 0.50
* <0.75 0.50
% <0.75 >0.50

Annual or seasonal mean speed and power values with the * (or %) symbol may not be very representative of the period of record because of significant data gaps. Annual or seasonal mean wind power with the # (or %) symbol may be as much as 20% in error because climatic mean air temperature were used to calculate the hourly (or 3-hourly) wind power values that went into the calculation of the mean value. Missing values, coded -99.9 for the wind speed and -999 for wind power, indicate no data were available to calculate the mean for that season. For a very small number of stations, errors in wind speed reporting or coding errors on the TD-1440 tapes resulted in anomalously high wind power densities for the month in which the error occurred. Negative wind power values, other than -999, are used to indicate that these high values have been replaced by the mean of the preceding and following months in the calculation of the annual and seasonal mean power.

References

Changery, M. J. 1978. National Wind Data Index. HCO/T1041-01, DOE/NOAA, E(49-26) 1041, National Climatic Data Center, Asheville, North Carolina.

NCDC. 1978. WBAN Station Numbers. National Climatic Data Center, Asheville, North Carolina.


Appendix D Evaluation of New Site Data for Verifying or Updating The Wind Resource Estimates

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