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Why ght is different between wrf's first output and era5 reanalysis forcing?

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BirdyBB

New member
Hi all,
Recently, I used WRFV4 1.5 simulating Typhoon Megi (2010). Lambert projection is used in the experiment, and the horizontal resolution is 5km. The ERA5 Reanalysis products provides the initial field of the model. I compared the reanalysis data with the results of the first time of the model output. Among them, the distribution of air temperature, specific humidity and wind field is basically similar, but the distribution of geopotential height(ght) field is different. Whether over the land or over the sea, the value of the ght at the initial time of WRF output is greater than the reanalysis data (500hPa isobaric surface is about 20m larger), and there are abundant messy contours in the land area. I wonder where this error comes from, how to solve this problem, and whether these departures can have a great impact on the experimental simulation results?

Can anyone help me?
Thank you! :D :D :D
 

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This is because the terrain is different between WRTF and ERA5. When REAL program processes the ERA5 data, it adjusts surface pressure and recalculate geopotential height. As a result, there is slight differences between WRF and ERA5.
 
Thank you so much for your reply! :D But what I can do to solve the problem, which the WRF's initial GHT is 20m higher than ERA5's. Whether the initial errors can cause great departures after integrating several days? Can nesting be a solution?
 
How did you interpolate GHT to 500hPa for wrfout_d01? i ask this because I found that the differences between wrfout and ERA are way too large.
 
I used two ways interpolating 500hPa GHT, one is wrf-python interplevel function(geopt = wrf.interplevel(GHT, FullModelPressure, 500)), the other is ARWpost. Both GHT patterns are the same. This picture is ARWpost's result.
 

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I am not that sure about the ARWpost, which is a pretty old package that has been obsolete for years.
The larger difference between ERA and wrfout, especially those over the ocean, makes me feel uneasy. I don't think the difference should be that large.
Have you compared the variable between wrfinput and ERA5, and also wrfinput and wrfout at the initial time?
 
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