The role of atmospheric internal variability on the tropical instability wave dynamics

The impact of atmospheric internal variability on tropical instability wave (TIW) activity in the eastern equatorial Pacific is examined. To diagnose the atmospheric internal variability, two simulations were performed with a state-of-the-art coupled general circulation model that uses an eddy permitting ocean component model. Standard coupling procedures are implemented in the control simulation. In the experimental simulation, the so-called interactive ensemble coupling is used, which systematically reduces the contribution of internal atmospheric dynamics to the air-sea fluxes of heat, momentum and fresh water. In the eastern equatorial Pacific, the reduction of the atmospheric internal variability leads to an enhancement of the available potential energy and higher exchanges from mean to eddy potential energy. The perturbations in the available potential energy and the eddy potential energy contribute to the enhancement in the TIW activity through the increased eddy kinetic energy. Due to the negative correlation between the atmospheric internal variability and TIW activity, the covariance between the momentum flux at the air-sea interface and the ocean surface currents as well as heat flux at the air-sea interface and the sea surface temperatures were nearly conserved west of 120 degrees W between the control and the experimental simulations.