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WRF-Lake model and SST update

This post was from a previous version of the WRF&MPAS-A Support Forum. New replies have been disabled and if you have follow up questions related to this post, then please start a new thread from the forum home page.


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Hi, I am testing the 1-D lake model available in current WRF by turning on sf_lake_physics = 1. As suggested by the user guide, I first generated the daily averaged near surface air temp (TAVGSFC), which was used for replacing the SST over Great Lakes. My question is when we turn on the lake model, should we still use sst_update =1 when we run long simulations? If we use sst_update =1, then the daily average air temp (TAVGSFC) will be used for updating SST over the lakes, which doesn't sound reasonable. if we do not use sst_update=1, then the lake surface temperature calculated by the lake model will be used as lower boundary conditions for the WRF? Thank you for any advice!
If you run with sf_lake_physics = 1, the Great Lakes will be treated as LAKE and the lake physics will be activated to predict TSK there. SST_UPDATE will only be effective over the ocean points. In this case, you don't need TAVGSFC to update TSK over the lake points.
Ming, thanks for your reply.

I have a follow-up question, if we DO NOT turn on sf_lake_physics, then the lake is treated as land (water body) or ocean? Should I turn on sst_update=1?

My domain is relatively small, covers Great Lake basins and have only a very small portion of Atlantic Ocean. If I turn on sst_updata=1, will the SST be updated for the Great Lakes (if they are treated as ocean)? if this is the case, then we may not want to use sst_update=1, because SST over Great Lake is not right anyways, and we don't have many grids over ocean.

Thanks for your advice.
Hi Jiali,
if you turn off sf_lake_physics, then the Great Lakes (and all other inland waterbody) will be treated as water point (similar to ocean water points). In this case, with sst_update, surface temperature at these inland water body will be updated.
If you only run a few days, it is right that you don't need to turn on sst_update. However, if you are running a climate simulation, then sst_update is still necessary even if your model domain only covers a small area of ocean. I agree with you that sst over the inland waterbody is not accurate partly because these inland waterbody cannot be well resolved in coarse-resolution GCM/analysis datasets.
And sorry I have another follow-up question:

In the wrfinput_d01, If we want to change the lake surface temp over Great lakes for the initial conditions, should we change TSK or SST in the wrfinput_d01? we did a test replacing SST over Great Lakes using another dataset in wrfinput_d01, and the output from wrfout is the same before and after the change of SST.

Thanks for your help!
Please change both TSK and SST in wrfinput. This is because once the model starts, TSK is the diagnostic variable that is equivalent to SST.
Ming, I have a follow-up question about TSK.

View attachment Archive.zipHow is TSK calculated over the Great Lakes? I am not using any lake model. I have a simulation, start from March 30th, the TSK starts having some abrupt ups and downs in April for about 10days. I also see similar phenomena in sensible ad latent heat flux (LH and HFX), which may be affected by the TSK? In addition, I see spikes in soil temp (TSLB), which affects the TSK? These spikes happen not everywhere over the lakes, but a part of Lake Superior, as you can see from the standard deviation map. Air temp (T2) looks reasonable, no spikes. I am using Noah land surface model. and I am using SST_update=1. The SST is from ERA5. The time series of SST looks reasonable, no spikes. No lake model.

Several possible reasons I could think of is (1) the SST in wrflowinp over that area at that time is close to 273K, maybe the LSM doesn't handle well? (2) TSLB calculation affect TSK which affect heat flux?

I am attaching a few figures for your reference. (1) time series of input SST (in wrflowinp) and output TSK and SST (from wrfout) from April 1st to Sep 30th. You can see the spikes for TSK but not input & output for SST. (2) standard deviation map for TSK over the 100 time steps in April during the spikes happening.

Thanks for your help!