'height_XXXhPa' fields are invalid when isobaric surfaces are below ground

[mgduda]

The 'height_XXXhPa' fields contain what appears to be the lowest model level terrain height where isobaric surfaces are below ground. See, e.g., this forum post about the 850 hPa heights.

One possible solution might be to modify the interp_tofixed_pressure routine so that missing values are inserted into the interpolated fields where the target surface is below the lowest model level or above the highest model level. This missing value should also appear as an attribute for the field in output files.

[mgduda]

Here's a quick look at the lowest model level height (left) and the 'height_850hPa' field (right) from a 24-h, 60-km simulation: