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.