This document describes the requirements and design of the time manager module in the Community Atmosphere Model (CAM). The time manager is built on top of the utilities for time management available from the Earth System Modeling Framework (ESMF)  libraries.
The time manager's user interface is provided via namelist variables which may be set to control simulation properties such as the timestep size, start date, and stop date. Dates are specified using either a Gregorian or a 365-day calendar.
The time manager's API provides the methods that are used to control the model's time loop, and provides date and time information to model procedures or modules that may need it. The API also provides an alarm facility which is designed to be used by parameterizations that need to carry out certain actions at specified times during the simulation. The alarms are set up during the initialization process, and are queried each timestep for their on/off status.