Augment source_type to provide description with identifier

[durack1]

Augment source_type to be self-describing, following Note 14 in http://goo.gl/v1drZl e.g.

{
   "source_type":{
      "AER":"aerosols: appears with AOGCM or AGCM in models that calculate tropospheric aerosols driven by emission fluxes, rather than relying on prescribed concentrations",
      "AGCM":"atmospheric general circulation model, including a land model",
      "AOGCM":"atmosphere-ocean global climate model",
...
}

[taylor13]

Here's my suggestions:

source_type = {
+    'AER':'aerosol treatment in an atmospheric model where concentrations are calculated based on emissions, transformation, and removal processes (rather than being prescribed or omitted entirely)'
+    'AGCM':'atmospheric general circulation model run with prescribed ocean surface conditions and usually a model of the land surface',
+    'AOGCM':'coupled atmosphere-ocean global climate model, additionally including explicit representation of at least the land and sea ice',
+    'BGC':'biogeochemistry model component that at the very least accounts for carbon reservoirs and fluxes in the atmosphere, terrestrial biosphere, and ocean',
+    'CHEM':'chemistry treatment in an atmospheric model that calculates atmospheric oxidant concentrations (including at least ozone), rather than prescribing them',
+    'ISM':'ice-sheet model that includes ice-flow',
+    'LAND':'land model run uncoupled from the atmosphere',
+    'OGCM':'ocean general circulation model run uncoupled from an AGCM but, usually including a sea-ice model',
+    'RAD':'radiation component of an atmospheric model run \'offline\'',
+    'SLAB':'slab-ocean used with an AGCM in representing the atmosphere-ocean coupled system'
+}

Hope they're correct and much clearer/cleaner. Do you see any mistakes? In particular, does an OGCM run uncoupled to the atmosphere usually include a sea-ice model?