Large winter cold bias over Europe

Hi all,
I'm currently running some hindcast simulations over Europe using WRF V3.8.1 driven by ERA-Interim and I have a very large cold bias (> 6C) during winter in the North Eastern part of the domain (see figure).
I tried several different configurations changing the land surface scheme as well as PBL, cumulus and microphysics parameterizations but I do not find an optimal combination able to lower the bias. I have also performed the same experiments with the last WRFV4.2.2 version but the bias remains large.
This patter is quite common in that region (https://journals.ametsoc.org/view/journals/clim/26/3/jcli-d-11-00676.1.xml), so I was wondering if anyone have ideas on how to reduce it.
Any suggestions would be greatly appreciated.

Hello,

The winter cold bias over Europe is indeed a common problem of WRF climate simulations, one we also bumped into recently.
We found that the underestimation in our case is mainly caused by erroneously large snow depths.
We resolved a large part of this issue by setting opt_snf=4 among the namelist options of the Noah-MP LSM (sf_surface_physics=4).
This instructs Noah-MP to partition the precipitation between snow and rain based on the model microphysics instead of some empirical relationships.

Varga, Á. J., & Breuer, H. (2020). Sensitivity of simulated temperature, precipitation, and global radiation to different WRF configurations over the Carpathian Basin for regional climate applications. Climate Dynamics, 55(9), 2849-2866.
https://doi.org/10.1007/s00382-020-05416-x

Regards,
Akos

Hi Akos,
thanks for the suggestion, I changed the land surface parametrization to Noah-MP setting opt_snf=4 but the bias is still there (> 6C :shock: ).
I also performed some tests trying to replicate the set up used in this study (https://link.springer.com/article/10.1007/s00382-015-2529-x) but I am not able to get the same results because of some bug fixes in the newer WRF version.

Any insights would be greatly appreciated.
Alessandro

Alessandro,
We are well aware of the cold T2 bias in winter, especially over snow cover area. This is a problem possibly related to soil physics, surface layer transfer and PBL scheme. We haven't figured out yet how to improve the model performance regarding the T2 cold bias. I am sorry.