[Wrf-users] Setting of RADT with multiple nests

[Eric Altshuler]

Dear WRF users,

Thanks to everyone who replied to my question. Again, the suggestions give conflicting advice, so I have decided to keep radt = 15, 15, 15 as I have done before. This setting seems to be a good compromise as it's neither too expensive (as 5, 5, 5 might be) nor result in too infrequent calls to the radiation parameterizations (as 45, 45, 45 would seem to be).

Best regards,

Eric L. Altshuler
Assistant Research Scientist
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
USA

E-mail: ela at cola.iges.org
Phone: (301) 902-1257
Fax: (301) 595-9793

----- Original Message -----
From: "Eric Altshuler" <ela at cola.iges.org>
To: "wrfhelp" <wrfhelp at ucar.edu>
Cc: "wrf-users" <wrf-users at ucar.edu>
Sent: Tuesday, March 31, 2009 7:13:46 PM GMT -05:00 US/Canada Eastern
Subject: Setting of RADT with multiple nests

Hello,

I have asked this question before, but I have never gotten a clear answer. I apologize for asking it again.

I am running WRF-ARW with 3 domains: a coarse grid at 45km resolution, an intermediate nest at 15km, and an inner nest at 5km. The WRF documentation says two things about RADT:

1. Set RADT (in minutes) equal to the horizontal resolution (in km), e.g. RADT = 10 for DX = 10000
2. Set RADT to be the same on all domains

These rules conflict when nesting is used. Obviously, with a 3:1 nesting ratio, it is impossible to satisfy both rules. My question is, which RADT setting should be used here?

a) radt = 45, 45, 45
b) radt = 15, 15, 15
c) radt = 5, 5, 5
d) none of the above?

My intuition is to set radt = 15, 15, 15 but I would appreciate feedback on how users deal with the RADT setting when they run WRF with nesting.

Thanks in advance for your attention.

Best regards,

Eric L. Altshuler
Assistant Research Scientist
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
USA

E-mail: ela at cola.iges.org
Phone: (301) 902-1257
Fax: (301) 595-9793