*is the temperature scale as calculated from eq. (18).
7.1.2 DIRECTIONALLY AND/OR MONTHLY VARYING SURFACE CHARACTERISTICS
Noon time albedo (rN ); Bowen ratio (Bo); roughness length (zo) - For AERMET, the user can
specify monthly variations of three surface characteristics for up to 12 upwind direction sectors.
These include: the albedo (r), which is the fraction of radiation reflected by the surface; the
Bowen ratio (Bo), which is the ratio of the sensible heat flux to the evaporation heat flux; and the
surface roughness length (zo) , which is the height above the ground at which the horizontal wind
velocity is typically zero. The user will be guided by look-up tables (in the AERMET user's
guide) of typical values for these three variables for a variety of seasons and land use types. The
information presented in the user’s guide is not be considered regulatory guidance. The user is
encouraged to research the literature to determine the most appropriate values for surface
characteristics, for a specific application.
Latitude; longitude; time zone; wind speed instrument threshold for each data set( uth ).
Solar radiation; net radiation (Rn); profile of vertical turbulence (Fw); profile of lateral
7.2Selection and Use of Measured Winds, Temperature and Turbulence in AERMET
7.2.1 THRESHOLD WIND SPEED
The user is required to define a threshold wind speed (uth) for on-site data sets. Although the
current version of AERMOD cannot accept a separateuth for NWS data, a separate uth should be
selected for each on-site data set being used.
7.2.2 REFERENCE TEMPERATURE AND HEIGHT
The reference height for temperature (zTref), and thus the reference temperature, is selected as
the lowest level of data which is available betweenzo & 100 m.
7.2.3 REFERENCE WIND SPEED AND HEIGHT
The reference height for winds (zref), and thus the reference wind speed (uref), is selected as the
lowest level of data which is available between 7zo & 100m. Although the current version of
AERMOD cannot accept a separatezref for offsite data, we believe that a separate zref should be
selected for each data set being used.
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