AERMOD Tech Guide
8.3.3 Reference Wind Speed & 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 can not accept a separate zref for offsite data, we believe that a separate zref should be selected for each data set being used.
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 calms policy).
All observed wind speeds in a measured profile that are less than uTH are set to missing and are therefore not used in the construction of the wind speed profile (profiling of winds is accomplished in AERMOD).