Boundary Values (conditions) and external constraints

The boundary values are values of the meteorological variables at the boundaries of the region being simulated. These values are presumably known and constrain the variables at specific locations. For instance, we know that the wind speed decreases closer to the ground and has a value of zero right at the ground surface. The zero wind speed at the ground is a boundary condition on the differential equation for wind.

External constraints are conditions imposed upon the computational domain (e.g., the atmosphere). For instance, solar heating is imposed from above the atmosphere and dictates the range of possible temperature values for the climate. A lower value (than present conditions) of solar heating might create an ice-age climate. The amount of greenhouse also is considered an external constraint. The albedo or reflectivity of the surface also is an external condition (unless it changes due to climate change, such as more ice due to global cooling).

Changing boundary conditions and external constraints

Adding or removing pegs from the pinball matrix is analogous to changing boundary conditions or external conditions. To remove a peg, simply move the arrow to a particular peg by using the mouse and click. Similarly, move the arrow to an open space and click to add a peg randomly in the matrix. This enables you to build a vertical fence or create a gap that constrains movement of the balls.