Bloated ARW cloud cover from UPP, fix here

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meteoadriatic
Posts: 1510
Joined: Wed Aug 19, 2009 10:05 am

Bloated ARW cloud cover from UPP, fix here

Post by meteoadriatic » Wed Sep 07, 2016 10:19 pm

Robert Rozumalski today updated EMS, and from his changes I got this idea to fix ARW cloud cover from original UPP code.

If you use original UPP code (not EMSUPP) for your WRF installation, and your cloud cover seems bloated like it comes from much coarser resolution, this is in fact by UPP design, not model problem. Unchanged UPP code for every grid point takes 30km radius around and calculates mean cloudiness in that radius. Why? Because, if you are located at that grid point, you will experience cloudiness not only because of cloud directly above your head, but also from clouds in area around you. This is especially good approach if you're extracting cloud cover values for particular points in your grid (for example for meteograms, tables and similar presentations), because it will give more realistic cloudiness value then if you take cloudiness just above your head (just for that grid point without taking cloudiness from area around you). But for maps, it doesn't look good, so if maps are your primary way of displaying products, you might want to change things little bit.

To fix that, navigate into source code, UPPV3.0/src/unipost/INITPOST.F and find "radius = 30000". There is only one occurence of that line in file so you can't miss it. Drop that value to whatever you like (those are meters) and recompile code. Significant differences will be seen when you decrease it below 15000, and If you really want to display "realistic like clouds", go very low with it. Try, test, find best value for your needs, but beware if you extract cloud cover for particular location and you don't do any type of area averaging on your own, better stay around 15000 meters with that value.

Also, if you go low enough with that radius, you should in theory fix issues where you see convective precipitation from isolated cumulus clouds without seeing clouds on that spot. This is, I think, beucase those small clouds become averaged out in that handling, so if you decrease enough this averaging radius, those "invisible clouds" should show up on your maps.

Hope this helps someone.

This is before (radius = 30000): http://www.meteoadriatic.net/pub/wrf/cl ... _30000.png
This is after (radius = 15000): http://www.meteoadriatic.net/pub/wrf/cl ... _15000.png

Notice the differences.

oib
Posts: 117
Joined: Mon Jan 31, 2011 3:29 pm

Re: Bloated ARW cloud cover from UPP, fix here

Post by oib » Thu Sep 08, 2016 3:46 pm

This is a major discovery, Ivan :)
Nice !!!

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