Yihua Luan, Yongqiang Yu, Weipeng Zheng

1. University Allied Workshop (2008-7-1) Numerical Study of the Influence of Indian Ocean Dipole Mode (IODM) on Tropical Pacific Ocean——Roles of the Ocean Dynamic Process Yihua Luan, Yongqiang Yu, Weipeng Zheng Institute of atmospheric physics, Chinese Academy of Sciences Dongliang Yuan Institute of Oceanology, Chinese Academy of Sciences

2. Outline • Introduction • Design of the experiments • Features of the OGCM simulation • The influence of IODM on the tropical Pacific Ocean 1、Results of the OGCM 2、Results of the CGCM • Summary

3. Introduction A composite Indian Ocean Dipole Mode event (Saji et al.,1999)

4. Introduction IODM could affect the tropical Pacific Ocean through atmospheric remote teleconnections or ocean internal dynamic process Atmospheric bridge: • IODM could strengthen the ongoing El Nino using observation data and numerical models to analyze the influence of Indian Ocean SST modes on the ongoing El Nino (Annamalai, et al 2005) • Westerly anomalies over the Indian Ocean could propagate to the tropical Pacific Ocean and affect El Nino (Qingchen Chao, et al 2001) • The Indo-monsoon circulation and the Pacific-Walker circulation have a strong coupling denoted as “GIP”, so the anomalies in the monsoonal zonal flow over the Indian Ocean can affect the air-sea interaction over equatorial Pacific by the virtue of the GIP and trigger off the occurrence of ENSO events (Meng Wen, Wu Guoxiong 2000,1998 )

5. Introduction IODM could affect the tropical Pacific Ocean through atmospheric remote teleconnections or ocean internal dynamic process Ocean internal dynamic process • The closure of ITF makes the eastern tropical Indian Ocean become cooler and western tropical Pacific Ocean become warmer （Hirst, A. C., et al.1993；Wajsowicz, R. C., et al.2001） Question: Can anomalous signal in the Indian Ocean affect Pacific circulation through the ocean internal dynamic process?

6. Design of the experiments

7. OGCM experiment 1997 Fig1 Indian Ocean dipole mode index from 1958-2000（East Indian Ocean: 90E-100E,10S-5N;West Indian Ocean:60E-80E,10S-0）

8. Features of OGCM simulation: SST anomalies

9. Features of OGCM simulation: upper ocean temperature anomalies

10. Indonesia Pacific Ocean Following the developing of the IODM, sea level anomalies appear in the Indonesia seas by June and migrate towards east. In August, weak SSH anomalies appear in the western tropical Pacific Ocean SSH anomalies migrate to the eastern tropical Pacific Ocean in September. A dramatically peaking of SSH anomalies occurs in December Results of the OGCM IODM effects on the SSH anomalies of Indonesia sea and Pacific Ocean

11. Pacific Ocean Indonesia IODM effects on the SST anomalies of Indonesia sea and Pacific Ocean

12. IODM effects on the upper Pacific Ocean temperature

13. Design of the CGCM experiments • FGOALS_g1.1: CAM2;LICOM1.11 • Coupled region: tropical Pacific Ocean (120E-80W,15S-15N) • Control experiment : climatological fields are specified over the regions out of the coupled region. • Sensitive experiment The wind stress anomaly, heat flux anomaly of ERA40 and the SST anomaly of GISST of the year 1997 are served as the forcing and the forcing is only applied in the Indian Ocean basin.

14. IODM effects on the tropical Pacific OceanResults of the CGCM SSTA

15. IODM effects on the tropical Pacific OceanResults of the CGCM SSHA

16. Regional Coupled Model In other years, tropical Pacific Ocean also makes response to the IODM. But there are different response in El Nino year and Lanina year. The influence process and the mechanism need more research work

17. Summary • The OGCM LICOM could simulate the IOD event from 1958-2000. • The upper ocean temperature anomalies and sea level anomalies related to the IOD events in the Indian Ocean propagate into the equatorial Pacific Ocean through the Indonesian Seas, and then produce significant SST and sea level anomalies in the eastern equatorial Pacific Ocean. • The regional coupled model could also simulate the propagation of the Indian Ocean abnormal signal into the Tropical Pacific Ocean through the wave process.

18. Comments and Suggestions! Thank you!