Response of the Atmosphere to Orographic Forcings: Insight from Idealized Simulations

Earth's orography profoundly influences its climate and is a major reason behind the zonally asymmetric features observed in the atmospheric circulation. The response of the atmosphere to orographic forcing, when idealized aqua mountains are placed individually and in pairs (180 degrees apart) at different latitudes, is investigated in the present study using a simplified general circulation model. The investigation reveals that the atmospheric response to orography is dependent on its latitudinal position: orographically triggered stationary waves in the midlatitudes are most energetic compared to the waves generated due to anomalous divergence in the tropics. The impact on precipitation is confined to the latitude of the orography when it is placed near the tropics, but when it is situated at higher latitudes, it also has a significant remote impact on the tropics. In general, the tropical mountains block the easterly flow, resulting in a weakening of the Hadley cells and a local reduction in the total poleward flux transport by the stationary eddies. On the other hand, the midlatitudinal orography triggers planetary-scale Rossby waves and enhances the poleward flux transport by stationary eddies. The twin mountains experiments, which are performed by placing orography in pairs at different latitudes, show that the energy fluxes, stationary wave, and precipitation pattern are not merely the linear additive sum of individual orographic responses at these latitudes. The nonlinearity in a diagnostic sense is a product interaction of flow between the two mountains, which depends on the background flow, the separation distance between mountains, and wind shear worldwide.