If no valid observation of the reference wind speed or direction exists between these limits
the hour is considered missing and a message is written to the AERMET message file. For the
wind speed to be valid its value must be greater than or equal to the threshold wind speed.
AERMOD processes hours of invalid wind speed, e.g. calms, in the same manner as ISC (EPA
All observed wind speeds in a measured profile that are less thanuth are set to missing and are
therefore not used in the construction of the wind speed profile (profiling of winds is
accomplished in AERMOD).
7.2.4 CALCULATING THE POTENTIAL TEMPERATURE GRADIENT ABOVE THE
MIXING HEIGHT FROM SOUNDING DATA
AERMET calculatesd2/dz for the layer above zi as follows:
- If the sounding extends at least 500 m abovezi the first 500 m above zi is used to
determined2/dz above zi.
- If the sounding extends at least 250 m abovezi (but not 500 m) then the available
sounding abovezi is used to determine d2/dz above zi.
- AERMET limitsd2/dz above zi to a minimum of 0.005 K m-1.
- If the sounding extends less than 250 m abovezi then set d2/dz = 0.005 K m-1 (a default
7.2.5 MEASURED TURBULENCE
All measured turbulence values are passed to AERMOD if the hour is non-missing. This is
true even for those levels where the wind speed is belowuth. Based on measurements with
research grade instruments, reasonable minimum turbulence levels in non-calm conditions for
vertical turbulence (Fw ) and lateral turbulence ( F
v) values are set by AERMOD to 0.02 m s-1 and
0.2 m s-1, respectively. Although these lower limits are applied to the measured values of the
turbulence the calculated profile values ofFw & F
vare not subjected to any lower limits. We do
not restrict these estimated profiles because it would bias the calculation of the effective values of
turbulence, which are averages through the layer between the receptor and the plume height, in
determining the dispersion of the plume. However, as discussed in Section 7.9 these limits are
applied to the effective values of turbulence and wind speed.
7.2.6 DATA SUBSTITUTION FOR MISSING ON-SITE DATA
If on-site data are missing for an hour, the hour is considered missing unless the user specifies
a substitute data set. AERMET does not default to NWS (or any other offsite) data.
n1001 - n1002 - n1003 - n1004 - n1005 - n1006 - n1007 - n1008 - n1009 - n1010 - n1011 - n1012 - n1013 - n1014 - n1015 - n1016 - n1017 - n1018 - n1019 - n1020 - n1021 - n1022 - n1023 - n1024 - n1025 - n1026 - n1027 - n1028 - n1029 - n1030 - n1031 - n1032 - n1033 - n1034 - n1035 - n1036 - n1037 - n1038 - n1039 - n1040 - n1041 - n1042 - n1043 - n1044 - n1045 - n1046 - n1047 - n1048 - n1049 - n1050
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