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

University Allied Workshop

(2008-7-1)

Dongliang Yuan

Institute of Oceanology, Chinese Academy of Sciences

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

Outline

Introduction

(Saji et al.,1999)

A composite Indian Ocean Dipole Mode event

Introduction

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 )

IODM could affect the tropical Pacific Ocean through atmospheric remote teleconnections or ocean internal dynamic process

Introduction

Ocean internal dynamic process The closure of ITF makes the eastern tropical Indian Ocean become co

oler 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?

IODM could affect the tropical Pacific Ocean through atmospheric remote teleconnections or ocean internal dynamic process

Design of the experiments

OGCM

(LICOM)

In the OGCM experiment, the daily ERA40 wind stress anomaly, heat flux anomaly from 1958-2000 are served as the forcing and the forcing is only applied in the Indian Ocean. The surface forcing over the other regions is the climatological fields

CGCM

(FGOALS_g1.1)

For the CGCM experiment, the regional coupled version of FGOALS_g1.1 is used, only the tropical Pacific (120E-280E,15S-15N) is coupled in the model. 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 Indian Ocean.

OGCM experiment

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

1997

Features of OGCM simulation: SST anomalies

Features of OGCM simulation: upper ocean temperature anomalies

IODM effects on the SSH anomalies of Indonesia sea and Pacific Ocean

Results of the OGCM

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

Indonesia

SSH anomalies migrate to the eastern tropical Pacific Ocean in September. A dramatically peaking of SSH anomalies occurs in December

Pacific Ocean

Indonesia

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

Pacific Ocean

IODM effects on the upper Pacific Ocean temperature

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 c

oupled 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.

IODM effects on the tropical Pacific OceanResults of the CGCM

SSTA

IODM effects on the tropical Pacific OceanResults of the CGCM

SSHA

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

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.

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