Impact of Indo-Pacific Oceans on Indian Monsoon and Cyclones

Tropical oceans are known to have great control on global atmospheric circulation. The

tropical Indo-Pacific Ocean stretching from the east coast of Africa to the west coast of

America has close coupling with the atmosphere on different timescales. There are two

dominant interannual variabilities in the Indo-Pacific oceans. The former is the El Nino

Southern Oscillation (ENSO) associated with SST variation in the Pacific Ocean . The two opposite phases of ENSO are El Nino and La Nina. During El Nino years, the trade winds weaken and reduce the upwelling of cold water off the coast of Peru, thus

create anomalous warming in the central and eastern tropical Pacific. The reverse occurs

in La Nina years with strengthened trade winds that store more heat in the western Pacific

Ocean.

Warming Indo-Pacific Ocean is found to alter the global rainfall patterns .

Increased atmospheric heating leads to the expansion of itswater holding capacity, produces

more intense precipitation events. Indian summer monsoon rainfall is directly

associated with strong cross-equatorial moisture transport to the Indian subcontinent from surrounding oceans . Intensification

of the atmospheric moisture transport into the Indian region has ramifications for

Indian summer monsoon rainfall (May, 2002). Therefore human-induced global climatic

warming can have a significant role in precipitation events around the world. A prominent

intraseasonal tropical climate variability called the Madden Julian Oscillation (MJO)

mainly seen over the Indo-Pacific Oceans, characterized by large-scale convective

cloud bands has a changed life cycle due to the expansion of Indo-Pacific warm pool.

Just as the ENSO in the Pacific, the Indian Ocean has a basin-scale variability in SST and

wind named Indian Ocean Dipole (IOD). The term IOD was coined by Saji et al. (1999).

They used an index named Dipole Mode Index (DMI), defined as the difference in SST

anomaly between the tropical western Indian Ocean and the tropical south-eastern Indian

Ocean. During positive IOD years (Positive DMI), the tropical south-eastern Indian Ocean

develops significant cooling, and tropical western Indian Ocean becomes abnormally warm

(Fig. 1.3a), which alter the atmospheric circulation pattern in the Indian Ocean region (Fig.

1.3). During the negative IOD years, the locations of the abnormal warmer/cooler ocean

temperature pattern and associated circulation pattern reverse.