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How Does a GCM Work?

So, what exactly goes on in a GCM? Each grid cell has a latitude and longitude, and it can have several layers in the vertical. The grid cell is given initial values for temperature, moisture, and wind speed at each level. Then, the equations in the model use those initial conditions to figure out conditions during the next time step.

convection Close to the surface, these values are used to determine if there should be convection. Convection is due to the fact that warm air is less dense than cold air - leading to warm air rising and cold air sinking. In the model, for example, if the surface is warmer than the layers above it, it will cool and the layers aloft will warm. The image below represents the action of warm air rising (or cold air sinking). condensation

Initial values of temperature and pressure also determine if conditions are right for water vapor to condense. Water vapor will condense if the temperature equals the dew point temperature. Condensation releases heat and can increase the temperature at certain levels in the grid cell.

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