Nonlinear stationary wave maintenance and seasonal cycle in the GFDL R30 GCM

In this study, the climatological stationary wave maintenance is examined f rom nonlinear perspective using the GFDL R30 GCM outputs, a fully nonlinear stationary wave model, and a linear stationary wave model. The primary foc us of the study is on the nature of the stationary nonlinearity and relativ e contribution to the total nonlinearity by various factors, such as heatin g, orography, and the interaction between flows forced by heating and orogr aphy. It is found that both the nonlinear effect of the diabatic heating an d the nonlinear interaction between flows forced by orography and diabatic heating are important contributors toward the total stationary nonlinearity in northern winter and summer. Some regional features, such as the anticyc lone off the northwest coast of North America in winter and the southwester n U.S. summer anticyclone, are entirely due to the nonlinear interaction be tween flows forced by heating and orography. Consistent with the linear stationary wave maintenance, the diabatic heatin g is the most dominant forcing mechanism in the Tropics and the Southern He misphere (SH) throughout the seasonal cycle in the nonlinear framework. Ove r the Northern Hemisphere (NH) extratropics during northern winter, however , the role of the orographic forcing is comparable to that of diabatic heat ing due to its strong nonlinear interaction with flows forced by heating an d transients. This contrasts significantly with the conclusion drawn from t he direct nonlinear responses in which the orography is much less important than the diabatic heating. The regional feature of the ridge over northwes tern North America in northern winter is found to be largely due to the pre sence of orography. The effect of transients in the nonlinear model, includ ing the nonlinear interaction of transients with flows forced by heating an d orography, shows a wave train over the Pacific-North American region (PNA ) that resembles the atmospheric response to El Nino. This differs consider ably from that in the linear view as well as that of the direct nonlinear r esponse to transients. Furthermore, it is found that the inclusion of orogr aphy or transients in the total stationary wave forcing improves the spatia l pattern simulation of the GCM stationary waves for both hemispheres in th eir respective winter months.