Below are the equations used to convert model u and v to earth-relative u and v:
u-earth = u-model*cosalpha - v-model*sinalpha
v-earth = v-model*cosalpha + u-model*sinalpha
where cosalpha and sinalpha can be found in model input and output files.
WPS rotates meteorological fields from source-grid to Earth-relative by having the logical flag is_wind_grid_rel set to .true. several places in the WPS source code. It will be set automatically based on input data, and therefore you do not need to change anything.
If you are preparing your own intermediate files, you will need to specify this variable.
There is an option that allows you to specify that the wind vectors be specified in Earth coordinates. The user may specify winds in Earth coordinates and have th WRF model internally rotate them to the WRF grid. To activate this capability, the user must specify a u- and v-component QC flag value of 129 for each wind vector that is to be rotated; otherwise, the model assumes the wind vector to be WRF grid-relative.
u-earth = u-model*cosalpha - v-model*sinalpha
v-earth = v-model*cosalpha + u-model*sinalpha
where cosalpha and sinalpha can be found in model input and output files.
WPS rotates meteorological fields from source-grid to Earth-relative by having the logical flag is_wind_grid_rel set to .true. several places in the WPS source code. It will be set automatically based on input data, and therefore you do not need to change anything.
If you are preparing your own intermediate files, you will need to specify this variable.
There is an option that allows you to specify that the wind vectors be specified in Earth coordinates. The user may specify winds in Earth coordinates and have th WRF model internally rotate them to the WRF grid. To activate this capability, the user must specify a u- and v-component QC flag value of 129 for each wind vector that is to be rotated; otherwise, the model assumes the wind vector to be WRF grid-relative.