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TOPIC: Visibility in HARMONIE-AROME

Visibility in HARMONIE-AROME 3 years 3 weeks ago #1768

  • Sander Tijm
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Dear all,

here is a link to an interesting study on the visibility and the cloud water concentration in China.

lageo.iap.ac.cn/uploads/141208013910429hgfl7rxpl.pdf

The interesting conclusion from this is that the Kunkel relations that we base our visibility upon give too high visibility in the very dirty air over China, whereas in our areas the visibility is too low when using the Kunkel relations. I think the visibility is better in our areas than you get from the Kunkel relations because the air is cleaner than when these relations were derived in 1980/81 (NE USA).

So probably it is good to make a correction for these relations where the visibility is higher, probably around a factor of 2 for the lowest visibilities and reducing this correction for higher visibilities.

I have tested something like vis=(1+(1-vis/1000))*vis (so no correction when the visibility is 1000m) and this draws the distribution much closer to the observed one.

Visibility in HARMONIE-AROME 3 years 2 weeks ago #1769

  • Lisa Bengtsson
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Hi Sander and others,

Sorry for my late response, I took a bit of a break over the holidays!

Regarding the RH2m Patrick has now included visibility verification in his 2-patch experiments.

hirlam.org/portal/smhi/HARMONIE_MONITOR/2_patches_export/
hirlam.org/portal/validation/40h1/2_patches_May2016_export/

In general we can see an improved RH2m with 2 patches (a reduced positive bias) over most sub-areas, followed by an improved visibility (a reduction of a negative bias), in particularly in March. In May the RH2m bias is still huge over northern Sweden, although improved with the 2-patches.

It doesn't solve everything, but it is in the right direction.

Your idea Sander about modifying the Kunkel (1984) formula for visibilities below 1000 m to account for "cleaner air", may be worth trying for comparison. Maybe in the future we could try to do something more sophisticated with real-time aerosol even for such a post-processed field.

Also, your remark above sounds interesting to update the visibility to remove the "lines".

Visibility in HARMONIE-AROME 3 years 2 weeks ago #1770

Dear Sander , Lisa and others

Thanks for recent info including results from China in relation to Kunkel
formula

I think we will have the opportunity to discuss the issues related to forecasting visibility in Toulouse from 16/1 -18/1

Hopefully this can also lead to a good follow up strategy

Best regards
Bent
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