[RegCNET] Terrain Information

[XUNQIANG BI]

Hi, Jared Bowden:

On Tue, 4 Mar 2008 jhbowden at ncsu.edu wrote:

> First, when RegCM uses reanalysis data, the user never explicitly gives
> any terrain information. How does RegCM know what the input terrain
> heights are?

The NNRP1/2 or ERA40 are at the pressure levels, so the terrain heights
are not necessary. (But terrain and surface pressure are required if you 
use GCM model level fields.)
>
> Second, and more generally, how does RegCM account for the variation of
> surface pressure during horizontal interpolation since terrain inevitably
> varies more in RegCM's finer grid than in the GCM's courser input data.
> Does RegCM just extrapolate hydrostatically from the more coarse GCM input
> surface pressure values to account for the terrain?

The way we did is that do the horizontal interpolation (bilinear) to model 
horizonal position at pressure levels firstly, then do the vertical 
interpolation (or extrapolation) in the vertical column.

Best Regards,
Xunqiang Bi

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Dr. Xunqiang Bi         email:bixq at ictp.it
   Earth System Physics Group
   The Abdus Salam ICTP
   Strada Costiera, 11
   P.O. BOX 586, 34100 Trieste, ITALY
   Tel: +39-040-2240302  Fax: +39-040-2240449
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