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This test case is described in the paper "A proposal for the 
intercomparison of the dynamical cores of atmospheric general 
circulation models" by Held and Suarez (HS94, Bulletin of the American 
Meteorological Society; 1994, Vol 75, 1825-1830), and you should read 
this paper for a detailed description of the test configuration and 
expected test results. 

This test of the global solver is dry (no moist effects or moisture), 
there is no terrain, and the flow is driven by an imposed forcing and 
dissipation. The forcing (a prescribed temperature distribution towards 
which the atmosphere is relaxed) and dissipation (a simple drag term in 
the lower atmosphere) produces midlatitude jets, breaking midlatitude 
baroclinic waves, etc. 

The default ARW namelist specifies a one-thousand day integration for 
this test - that is approximately the length of the simulations 
presented in HS94, where statistics of the flow are calculated using 
time averaged fields from the last few hundred days of the simulations. 
The midlatitude jets and baroclinic instabilities appear early (within 
the first 100 days) so long integrations are not required to observe 
the main features of the flow. The default ARW configuration for this 
test case is very coarse - much coarser horizontal resolution than that 
presented in HS94, so care should be taken in comparing any results from 
the default configuration to the HS94 results (the coarse grid allows 
one to run the long simulation on a single processor of a present-day 
PC). The HS94 results are presented in the form of vertical cross 
sections of zonal means, which are not standard analysis plots for the 
ARW plotting packages. The results are also sensitive to the horizontal 
dissipation (numerical filters) used in these simulations. 

There is no exact solution for this test, so the results can only be 
compared with that from others models in a qualitative manner.
