Impact of the Madden-Julian Oscillation on convection and circulation in the subtropics to midlatitudes in the IPCC AR4 Simulations

Ｉmpact on convective activity and circulation in the subtropics to midlatitudes of the Madden-Julian Oscillation (MJO) is statistically investigated. The ability of simulations is assessed using coupled ocean-atmosphere climate models in the Coupled Model Inter-comparison Project 3 (CMIP3) for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The observational analysis shows that the belt of positive convective anomaly appears over the subtropical Asia to the Western North Pacific (STA-WNP) in the boreal winter (November-March) when the convection associated with MJO in the tropical Indian Ocean (TIO) is active. This is attributed to be the active moisture transport with the low-level southwesterly anomaly from the tropics due to significant generation of the NP high pressure anomaly with the change of MJO phase. The low-level temperature anomaly in STA-NWP is concurrently found to be positive in the active phase of MJO over TIO. On the contrary, the convective negative anomaly is shown with the anomalies of divergence and cold temperature in STA-WNP when the convection associated with MJO is active over the maritime-continent to the Western Pacific (WP). Analysis in the inter-comparison of models with observation indicates that about 8 models have high skill of convective anomalies with the MJO in TIO to WP and exhibit eastward propagation of convective anomalies. Those models also produce the convective positive anomaly in STA-NWP and high pressure anomaly in NP. However, some (about 4) models in high skill models of MJO represent positive anomaly of the moisture flux convergence, and only a few models do positive anomaly of the low-level temperature in STA-NWP. Some models exhibit positive temperature anomaly in STA-WNP even though the simulation skill of MJO in the tropics is low. The results suggest difficulty in simulating the convective-circulation interaction with MJO between the tropics and STA to mid-latitudes. In the boreal summer to autumn, the circulation in the active phase of MJO affect the generation and track of tropical cyclone. Therefore, correctly representing extratropical-tropical interactions associated with MJO throughout the year is important for predicting climate change. From best models in the twentieth-century integrations, the changes of convective-circulations with MJO in the global warming runs are discussed.