Soil Temperature
                              ---- -----------

The soil model consists of 3 layer:

  	    depth	GRIB description

	  0 -  10 cm	0-10cm (10.dlr)		top layer
	 10 - 200 cm	10-200cm (200.dlr)	middle layer
	200 - 400 cm	300cm (300.dpl)		bottom layer

The GRIB description for the bottom layer is imprecise because of a 
flaw in GRIB which does not allow encoding of a 200-400 cm layer.

The annual cycle in the soil temperature decreases in amplitude with 
depth.  The model assumes that the bottom layer has no time variations
of temperature (not a bad assumption).  The temperature of the
bottom layer is set to the annual-mean surface temperature climatology
so that the net heat flux from the bottom layer should be approach
zero.