Geostrophic wind for WRF SCM


New member
Hi all!

I am running WRF SCM and to force it by tendencies from the WRF 3D model. The 3D model uses IFS HRES as host model for the analysis and boundary values. Before I ran ideal cases with a constant geostrophic wind. Now I am forcing it with values from WRF 3D. Everything works fine, but I have problems to calculate the geostrophic wind from WRF 3D, which is needed to run real-time SCM cases. The WRF 3D analysis is just an interpolation from the IFS field at that time. In this case 06 UTC.

I am running WRF4.4 and WRFSCM4.3.3 with a Lambert coformal projection over Scandinavia. Horizontal resolution is 3000 m. Raa is the density.

I am calculating the geostrophic wind according to the following formulas, where I can choose longitude and latitude:

U_G_WRF = -1/(Raa*f) * (P_TOT[0, :, LATITUDE+1, LONGITUDE] - P_TOT[0, :, LATITUDE-1, LONGITUDE])/(2 * 3000)
V_G_WRF = 1/(Raa*f) * (P_TOT[0, :, LATITUDE, LONGITUDE+1] - P_TOT[0, :, LATITUDE, LONGITUDE-1])/(2 * 3000)

I have attached 2 figures from a gridpoint close to Sodankylä in northern Finland.

Figure 1: WRF and IFS wind, and geostrophic wind, at time zero, where I have rotated the WRF winds according to:

Uearth = U*cosalpha - V*sinalpha
Vearth = V*cosalpha + U*sinalpha

The total wind in WRF and IFS HRES is equal after interpolation, so the WRF winds seems properly rotated. The geostrophic wind, on the other hand, is displaced along the x-axis but have the same shape as in the IFS HRES. The geostrophic wind is also rotated according to the formulas above after calculation of U_G and V_G.

Figure 2:

The same plot in a 9-hour simulation where I have made the calculations in the same way. Now the geostrophic wind looks better, except for altitudes above 10 km. I guess it depends on small pressure gradients at higher altitudes. It looks the same at high altitudes in IFS HRES, but the oscillations are smaller. I can skip the geostrophic wind at higher altitudes, but WHAT IS WRONG WITH THE GEOSTROPHIC WIND AT TIME 0?

Thankful for help!


Martin Hagman, Stockholm, Sweden


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