Julie Prestopnik wrote: > My supervisor asked me to pass along this question: > > The attached files pertain to the Denver snowstorm on 12/20/06. In the > input to METRo, 28cm of snow fall during the first 33 hours. The cloud > cover is complete throughout that time period. The road temperature is > below 0C through the entire period. If the road is below freezing, I > would not expect any runoff since the precipitation does not turn to > liquid. Yet, the snow depth never gets above 1.7cm. I understand that > some compaction may be taking place, but standard snow-to-liquid > ratios are near 10-1. This compaction ratio is well beyond that. Where > does all the precip go? > > Is there an implicit traffic model within METRo? Or, is the snow > carried away by the wind? I'm just grasping for possible explanations... > > > -Julie > Hi Julie,
Excellent question and the timing of it is very surprising. I did a commit of file lib_therm.f this morning: I have translated the comments of the subroutine RODCON (for road condition). Everything about the water/snow runoff is in this routine. In simple words, there is a value (MEA in lib_therm.f) that is used to parametrize this runoff. From the publication of METRo in JAM, page 2029, it is written: « Snow removal, either by traffic or maintenance operations, is also parameterized with the same exponential relaxation function, with WS replacing Wl in (10). This parameterization stems from the observation that the passage of cars tends effectively to remove all but a thin layer of snow at the road surface. » You can play with the different variables controlling the runoff. Mainly MEA and the factors "3e-3" and "3e-4" used in the computation of ER1 and ER2. If you have some remarks/comments/questions about those parameters, do not hesitate since these are assumptions. Miguel _______________________________________________ METRo-developers mailing list [email protected] https://mail.gna.org/listinfo/metro-developers
