Differences of Boreal Summer Intraseasonal Oscillations Simulated in an Atmosphere–Ocean Coupled Model and an Atmosphere-Only Model*

Abstract

A series of small-perturbation experiments has been conducted to demonstrate that an atmosphere–ocean coupled model and an atmosphere-only model produce significantly different intensities of boreal summer intraseasonal oscillation (BSISO) and phase relationships between convection and underlying SST associated with BSISO. The coupled model not only simulates a stronger BSISO than the atmosphere-only model, but also generates a realistic phase relationship between intraseasonal convection and underlying SST. In the coupled model, positive (negative) SST fluctuations are highly correlated with more (less) precipitation with a time lead of 10 days as in the observations, suggesting that intraseasonal SST is a result of atmospheric convection, but at the same time, positively feeds back to increase the intensity of the convection. In the atmosphere-only model, however, SST is only a boundary forcing for the atmosphere. The intraseasonal convection in the atmosphere-only model is actually less correl... Abstract A series of small-perturbation experiments has been conducted to demonstrate that an atmosphere–ocean coupled model and an atmosphere-only model produce significantly different intensities of boreal summer intraseasonal oscillation (BSISO) and phase relationships between convection and underlying SST associated with BSISO. The coupled model not only simulates a stronger BSISO than the atmosphere-only model, but also generates a realistic phase relationship between intraseasonal convection and underlying SST. In the coupled model, positive (negative) SST fluctuations are highly correlated with more (less) precipitation with a time lead of 10 days as in the observations, suggesting that intraseasonal SST is a result of atmospheric convection, but at the same time, positively feeds back to increase the intensity of the convection. In the atmosphere-only model, however, SST is only a boundary forcing for the atmosphere. The intraseasonal convection in the atmosphere-only model is actually less correl...