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The coupler communication frequency is an integer number of times per NCPL_BASE_PERIOD. The atmosphere's coupling frequency is NCPL_ATM. The frequency depends on the component set and the grid and the options are in the driver's config_component.xml seen in https://github.com/E3SM-Project/E3SM/blob/mastermaint-1.0/cime/src/drivers/mct/cime_config/config_component_e3sm.xml.
In a fully coupled case, the NCPL_ATM =48. With a base period of 1 day, the atmosphere communicates with the coupler very 30 simulated minutes. The longest time step for the atmosphere (dtime) is also set to 30 minutes. (The "dtime" variable in the atmosphere namelist is ignored). The atmosphere may (and often does) subcycle parts of its solve within that 30 minutes.
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