Wind parameters available through the POWER API and DAV include wind speeds and direction at various heights above the surface. The user community choice determines the exact height availability.
Mean Wind Speed and Wind Direction Parameters
The wind speed and wind direction parameters are to be used to determine the mean wind flow of a region rather than local area due to effects of buildings and local topography.
Corrected Wind Speed¶
In addition to the wind speed parameters available at set heights above surface, the POWER API allows the user to request a wind speed at a user defined height (between 10 and 300 m) for a particular wind-surface type.
Equation: Corrected Wind Speed (Adjusted For Elevation)
|vegtype_1||35-m broadleaf-evergreen trees (70% coverage)||vegtype_7||0.6-m perennial groundcover (100%)|
|vegtype_2||20-m broadleaf-deciduous trees (75% coverage)||vegtype_8||0.5-m broadleaf shrubs (variable %) & groundcover|
|vegtype_3||20-m broadleaf and needleleaf trees (75% coverage)||vegtype_9||0.5-m broadleaf shrubs (10%) with bare soil|
|vegtype_4||17-m needleleaf-evergreen trees (75% coverage)||vegtype_10||Tundra: 0.6-m trees/shrubs (variable %) & groundcover|
|vegtype_5||14-m needleleaf-deciduous trees (50% coverage)||vegtype_11||Rough bare soil|
|vegtype_6||Savanna:18-m broadleaf trees (30%) & groundcover||vegtype_12||Crop: 20-m broadleaf-deciduous trees (10%) & wheat|
|vegtype_20||Rough glacial snow/ice||seaice||Smooth sea ice|
|openwater||Open water||airportice||Airport: flat ice/snow|
|airportgrass||Airport: flat rough grass|
Wind Speed Validation¶
In this section, MERRA-2 10-meter wind speed is compared to observations reported to the National Center for Environmental Information (NCEI – formerly National Climatic Data Center). Selected surface sites from the NCEI Integrated Surface Database (ISD) files are used for the hourly MERRA-2 comparisons. Global "Summary of the Day" (GSOD) files are used for the comparison to the daily mean MERRA-2 temperature.
Hourly Wind Speed
Scatter plot of the MERRA-2 hourly 10-meter wind speed vs. the hourly station observations values from the selected NCEI ISD files for the years 2001 - 2019.
The hourly validation scatter plot exhibits a large concentration of pairs for wind speeds < 10 m/s and shows that the surface site values have a larger range in general than the MERRA-2 data. The total number of hourly pairs is 225,364,116.
Daily Average 10-meter Wind Speed
Scatter plot of the re-gridded MERRA-2 daily wind speed vs. the daily station observations values from the NCEI GSOD files for every 3rd year from 1981 – 2014.
The color bar along the right side of the scatter plot provides a measure of the distribution of the NCEI, MERRA-2 wind speed pairs in bins of 1 m/s. For example, the left column along the vertical color bar shows that each data point in dark blue represents the number ground site/MERRA-2 data pairs within 10% (i.e. <=74,628.4) of the maximum number of data pairs within a 1 m/s bins in the plot (i.e. 746,284). Additionally, from the right side of the vertical color bar it can be seen that all the points shown in dark blue contain 17.25% of the total number of ground site, MERRA-2 data pairs (8,832,141). The remaining 82.75% of the data pairs are concentrated along the 1:1 grey line in the lower left corner for wind speeds < 10m/s.
Wind Direction at a given height in degrees as the meteorological convention. The meteorological convention gives the direction from which the wind originates and wind direction is measured in degrees clockwise from due north.
The computation of wind direction from MERRA-2 u and v components is based upon the information from NCAR/UCAR/EOL's quick reference on wind direction. Verification of the equations is accomplished with the usage of MERRA-2 10 meter winds from July 11, 2015; shown in this table:
|Latitude||Longitude||u (ms-1)||v (ms-1)||direction|
These locations are shown as the red circles on the streamline map here.
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