PCCM2 is a message-passing implementation of the NCAR Community Climate
Model 2 (CCM2). In September 1993, PCCM was officially validated with
respect to the sequential version of CCM. The SP1 was used extensively
in the validation work because its nodes are identical to workstation
platforms running the previously validated sequential version. The
first validated version of PCCM ran on the SP1.
The model is patch decomposed in two horizontal dimensions. Spectral
transport of all prognostic variables except moisture is accomplished
by parallel FFTs in the zonal dimension and Gaussian quadrature in the
meridional dimension, approximating Legendre transforms. The spectral
transport mechanism of CCM2 is communication intensive because
interchange of data is not confined to nearest neighbor. A
semi-Lagrangian transport scheme is used for transport of moisture.
Modules that compute atmospheric processes such as convection,
radiative transfer, and precipitation are collectively known within the
model as <#212#> physics<#212#>. Physics is perfectly parallel in PCCM because
there are no horizontal data dependencies; however, physics does
present the largest source of inefficiency from load imbalance.
PCCM2 was implemented using Chameleon through a compatibility library to
PICL, the message-passing package under which the code was originally
developed. Before being run on the IBM <#213#>SP1<#213#>, PCCM2 was run on the Intel
Touchstone DELTA and Paragon computers.
PCCM ran at approximately 650 Mflops on the full <#214#>SP1<#214#>
(128 processors)
communicating over the EUIH switch interface. Figure #figpccm2use#215>