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20km vs 13km RUC topography

Posted By: Jack Glendening
Date: 6-June-05 0113Z

I've been comparing topography from the 20km and 13km RUC models for
California with results puzzling to me, since if I put them
side-by-side they look very similar -- in fact if I didn't know
otherwise, I would choose the 20km topo as providing better definition
of the terrain features. This leads me to ask whether there has been
some additional filtering used for the 13km grid terrain, vis-a-vis
that used to generate the 20km terrain?

An example is that whereas the 20km grid had a rudimentary resolution
of the Owens Valley separating the Sierras from the White Mts
paralleling them to the east, in the 13km terrain those features are
smoothed out. I realize that some of this can be ascribed to the fact
that a point may by happenstance have occurred at a ridgeline for the
20km but not for the 13km terrain, and the use of envelope topography.
But those cannot account for the fact that a point common to both
grids, which lies in the Owens Valley with an actual elevation around
4700 ft, has a grid elevation of 6367 ft in the 20km terrain but a
higher one of 7246 ft in the 13 km terrain grid. I cannot see how the
elevation of that point would be increased further away from the
actual terrain height as the resolution is decreased unless the
smoothing has been increased.

I've created an image depicting the two terrains over identical areas,
pointing out the common "Owens Valley" point in both, at
http://www.drjack.info/MISC/POSTS/sierra-whites.20-13km.montage.png

While I've concentrated on the above feature, there other puzzles --
such as the fact that the widths of the mountains surrounding LA are
essentially the same in both, even though a much smaller resolution
would be needed to truly resolve them -- all of which would be
explained if the smoothing had been increased for the 13km terrain
generation.

Jack

Messages In This Thread

20km vs 13km RUC topography -- Jack Glendening -- 6-June-05 0113Z
Re: 20km vs 13km RUC topography -- Stan Benjamin -- 6-June-05 1308Z
Re: 20km vs 13km RUC topography - Jack is right -- Stan Benjamin -- 23-June-05 0009Z

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