Our linear and nonlinear models simulate the changes of stationary wave patterns over the US in summer fairly well. The stationary wave response to individual forcings, such as diabatic heating, orography and transients, are examined. The combination of orographic forcing and diabatic heating is capable of reproducing the change in stationary wave pattern indicating that diabatic heating and orographic forcing play an important role in the stationary wave changes in summer. The non-linear interaction between these two forcings is the dominant part of the non-linear interaction term. The role of transient forcing was found to be negligible. The importance of orographic forcing has been further emphasized through the role of changes in the basic state that contribute significantly to the changes in stationary wave maintenance.
An examination of the stationary wave features associated with interannual variations of the wet and dry North American monsoons will also be performed in the near future.