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Discussion about vertical levels

Since Vis5d is designed mainly for dealing with 3-dimensioonal data, some problems arise when 2-dimensional fields are considered, especially if they don't lye on a coordinate Vis5d surface, such as surface fields. For this reason an additional level should be added at the beginning of the input level list (tablev) to specify the ground; in terrain-following coordinates this should coincide with a coordinate surface having a value of 1, while for pressure or height surface this should have a fictitious value, maybe 0.

In the case of terrain-following coordinates, fields that are stored in the lowest level can be either (near) surface fields (with nl=1 and lowlev=0) or lowest model level fields (with lowlev=0); this also allows to mix variables defined only in the upper-air levels, such as temperature of wind, with the corresponding near-surface variable, such as 2m temperature or 10m wind. Moreover, if the flag fill_below is enabled (and it is by default) all the fields that are defined at the model surface are extrapolated with constant value below the orography up to the sea level, so that their surface value can be visualized in a horizontal cross-section at 0 height.


next up previous contents
Next: Quick guide Up: GRIB2V5D USER'S GUIDE Converting Previous: Optional output files   Contents
Davide
2002-04-04