Sea surface temperature associations with the late Indian summer monsoon

Pascal Terray (1) , Pascale Delécluse (1) , S. Labattu (1) , Laurent Terray (2)

1 LODYC - Laboratoire d'océanographie dynamique et de climatologie
2 CERFACS - Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique

This paper uses recent gridded and historical data in order to assess the relationships between interannual variability of the Indian Summer Monsoon (ISM) and Sea Surface Temperature (SST) anomaly patterns over the Indian and Pacific oceans. Interannual variability of ISM rainfall and dynamical indices for the traditional summer monsoon season (June-September) are strongly influenced by rainfall and circulation anomalies observed during August and September, or the Late Indian Summer Monsoon (LISM). Anomalous monsoons are linked to well-defined LISM rainfall and large-scale circulation anomalies. The east-west Walker and local Hadley circulations fluctuate during the LISM of anomalous ISM years. LISM circulation is weakened and shifted eastward during weak ISM years. Therefore, we focus on the predictability of the LISM in this study. Strong (weak) (L)ISMs are preceded by significant positive (negative) SST anomalies in the southeastern subtropical Indian Ocean, off Australia, during boreal winter. These SST anomalies are mainly linked to south Indian Ocean dipole events, recently studied by Behera and Yamagata (2001), and to the El Niño-Southern Oscillation (ENSO) phenomenon. These SST anomalies are highly persistent and affect the northwestward translation of the Mascarene high from austral to boreal summer. The southeastward (northwestward) shift of this subtropical high associated with cold (warm) SST anomalies off Australia causes a weakening (strengthening) of the whole monsoon circulation through a modulation of the local Hadley cell during the LISM. Furthermore, it is suggested that the Mascarene high interacts with the underlying SST anomalies through a positive dynamical feedback mechanism, maintaining its anomalous position during the LISM. Our results also explain why a strong ISM is preceded by a transition in boreal spring from an El Niño to a La Niña state in the Pacific and vice versa. An El Niño event and the associated warm SST anomalies over the southeastern Indian Ocean during boreal winter may play a key role in the development of a strong ISM by strengthening the local Hadley circulation during the LISM. On the other hand, a developing La Niña event in boreal spring and summer may also enhance the eastwest Walker circulation and the monsoon as demonstrated in many previous studies.

Mots clés: Indian Summer Monsoon; El Niño-Southern Oscillation; Indian Ocean; coupled interactions

Domaines: Géophysique [physics.geo-ph]; Milieux et Changements globaux; Océan, Atmosphère

Pascal Terray, Pascale Delécluse, S. Labattu, Laurent Terray. Sea surface temperature associations with the late Indian summer monsoon. Climate Dynamics, 2003, 21, pp.593-618. ⟨10.1007/S00382-003-0354-0⟩. ⟨hal-00770815⟩