wind speeds is even more complex in real world applications given the typically patchy nature of
the heterogeneity of surface roughness elements.
The recommended upwind distance for surface roughness should take into account the fact that
surface roughness effects in AERMOD are more important for stable atmospheric conditions
than for neutral/unstable conditions, and that meteorological monitoring sites are typically
characterized by open (low roughness) exposures in order to accommodate recommended siting
criteria (EPA, 2000). For typical measurement programs, including NWS stations, the reference
wind measurements will be taken for an anemometer height of approximately 10 meters above
ground. An upwind distance based on the recommended siting criterion of at least 10 times the
height of nearby obstacles (EPA, 2000), which would correspond to a distance of about 100m for
typical obstacles such as trees and 2-3 story buildings, is considered inadequate for this purpose.
However, the previous recommendation to use an upwind distance of 3 kilometers for surface
roughness is considered too large because the boundary layer up to typical measurement heights
of 10m will generally respond to changes in roughness length over much shorter distances.
Including land cover information across an upwind distance that is too large could misrepresent
the amount of mechanical turbulence present in the approach flow and bias model results,
especially for low-level releases.
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castellano: DISPER CUSTIC DESCAR RADIA italiano:
deutsch: DIS CUS DES RAD
castellano: DIS CUS DES RAD english: DIS CUS DES RAD
português: DIS CUS DES RAD italiano: DIS CUS DES RAD
français: DIS CUS DES RAD