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This implementation of parallelism for climatology generation once had relatively poor granularity. Meaning that nodes using background or parallel mode always computed 12 monthly climatologies simultaneously, and nodes using serial mode always computed only 1 climatology at a time, and there was no granularity in between these extremes. The '-j job_nbr' option (also in ncremap) allows the user to specify the exact granularity to match the node's resources. Here job_nbr specifies the maximum number of simultaneous climo tasks (averaging, regridding) to send to a node at one time. The default value of job_nbr is 12 for monthly climatologies in both MPI and Background parallelism modes. This can be over-ridden to improve granularity. For example, if job_nbr=4 is explicitly requested, then the 12 monthly climos will be computed in three sequential batches of four months each. In MPI mode ncclimo automatically sets job_nbr to the number of nodes available when working in splitter (not climo) mode, so invoking ncclimo with four nodes in splitter mode means each of those the four nodes will , be default, receive on climo task at a time unless the user explicitly specifies a different job_nbrreceive one splitter task. In Background mode job_nbr defaults to 12 and if job_nbr is explicitly specified, say with job_nbr=4, then those four months are computed simultaneously on the host node. Some nodes, e.g., your personal workstation, are underpowered for 12 climo tasks yet overpowered for 1 task, and so benefit from improved granularity.
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