Package for reading and processing Community Land Model (CLM) vector output, in particular useful for processing multiple elevation class (MEC) output over glaciated landunits.

What is vector output?

Normal CLM output is layed out on a latitude/longitude grid with each number representing the grid cell average value. However, internally CLM grid cells are made out of columns, for instance crop, lake and swamp. Each column has a type called a "landunit", we refer to the CLM User Guide for more details. In order to retrieve the column output one can set

hist_dov2xy = .false. 

in the CLM namelist. Instead of a structured lat-lon grid, the output is now unstructured and each value represents a column. This we call column or vector output.

Multiple elevation classes

Here, we are interested in the vertical distribution of energy and mass over glaciers. CLM is capable of using "Multiple Elevation Classes" (ref Lipscomb 2013), a subgrid scale parameterization which basically boils down to the fact that we have a independent CLM glacier columns at different heights within a grid cell. The values at different heights can be obtained from the vector output (see above).

This package

The goal of this package is to take the unstructured vector output and turn that into something more useable: a structured lat-lon 3d gridded field. The core of this package is the VectorMecVariable class which represents exactly one variable stored in one vector history file.

Input

The package works on CLM vector history output. Standard CESM runs do not have this! To generate vector output, add e.g. these lines to your user_nl_clm:

   hist_nhtfrq = 0,-24,0
   hist_mfilt = 1,1,1
   hist_dov2xy = .true., .true, .false.
   
   ! Daily output
   ! hist_fincl2 = 'QSNOMELT'
   
   ! monthly, vector
   hist_fincl3 = 'QICE`

which define three output streams. Stream one (*.h0.*.nc) contains the gridded monthly data, stream two (*.h1.*.nc) contains daily gridded data and stream three (*.h2.*.nc) contains unstructured monthly vector data.

Importing the package

Include package from a relative path:

sys.path.insert(0, "..")
from libvector import VectorMecVariable

or from an absolute path:

sys.path.insert(0, "/glade/u/home/lvank/github/libvector/")
from libvector import VectorMecVariable

Examples

see the examples directory.

Usage notes

Some operations require additional information, for instance the ice cover or the topographic height of columns. Alas, the documentation about this still needs to be written. Luckily, the package will yield a somewhat helpful error message in case a requirement hasn't been met.

Getting help

Create an Github issue at https://github.com/lvankampenhout/libvector or contact me at [email protected]