Wind speed treatment under calm conditions

CMAQ
1

Hello, there.

Im aware that some air quality models treat all wind speed values under 1m/s as 1m/s. I was wondering if CMAQ does the same.

I compared values for wind speed at 10m and they are exactly the same in the wrfout file and in the METCRO2D file and the same happens with u-wind and v-wind in the METDOT3D file. So my first impressions is that CMAQ does not change wind speed values under 1m/s.

Am I correct here or I am missing something? Maybe there is a some consideration somewhere in the code that converts wind speed under 1m/s to 1m/s?

Thank you in advance
Sol

2

This practice is generally found in observation-driven models, for which the observing instruments tend to have a response-threshold of about 1 M/S (and report 0 below that threshold). For such models – which WRF (and WRF-driven CMAQ) are not – using the observationally-reported zero would bias the model’s wind down under relatively-calm conditions.

3 Likes
3

Thank you for your quick answer!