Relationship between the Indo-western Pacific Ocean capacitor mode and Indian summer monsoon rainfall in CMIP6 models

• Published in: Climate dynamics 2022-07, Vol.59 (1-2), p.393-415
• Main Authors: Darshana, P., Chowdary, Jasti S., Parekh, Anant, Gnanaseelan, C.
• Format: Article
• Language: English
• Subjects: Anomalies; Anticyclones; Atmospheric circulation; Atmospheric models; Capacitors; Climatology; Correlation; Coupled modes; Dipoles; Earth and Environmental Science; Earth Sciences; El Nino; El Nino phenomena; Environmental aspects; General circulation models; Geophysics/Geodesy; Global climate; Intercomparison; Modelling; Monsoon forecasting; Monsoon rainfall; Monsoons; Ocean models; Ocean-atmosphere interaction; Oceanography; Oceans; Rain; Rain and rainfall; Rainfall; Rainfall anomalies; Rainfall patterns; Rainfall simulators; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Summer; Summer monsoon; Surface temperature; Tropical climate; Variability; Wind
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-021-06133-9

The Indo-western Pacific Ocean capacitor (IPOC) mode is an air-sea coupled mode of variability involving inter-basin interaction between the tropical Indian Ocean (TIO) Sea surface temperature (SST) and western-north Pacific (WNP) atmospheric circulation. The present study examined the fidelity of the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison Projects phase-6 (CMIP6) models (40) in representing the relationship between the IPOC mode and Indian Summer Monsoon (ISM) rainfall in historical simulations. Observations show that the positive phase of IPOC mode, linked with WNP anticyclone and TIO warming, induces a southwest-northeast (positive–negative) dipole rainfall pattern over the Indian land region on an interannual timescale. Many CMIP6 models show good skill in capturing the IPOC mode. However, only ~ 30% (12 out of 40) models are able to represent the ISM rainfall patterns associated with IPOC mode well. Physical mechanisms that explain the dipole-like rainfall pattern over India associated with IPOC mode are discussed in those models. It is noted that the persistent SST anomalies in the central equatorial Pacific, and excess cooling over the north Pacific are mainly responsible for the misrepresentation of teleconnections between the IPOC and ISM in many models. The interdecadal modulations between the IPOC mode and ISM rainfall is evaluated in the selected 12 models by means of a 21-year sliding window correlation. Based on this, high correlation epoch (HCE) and low correlation epoch (LCE) are selected for further analysis. The IPOC mode and positive rainfall anomaly over southern peninsular and western India are well simulated in selected models during HCE with some discrepancies. In the case of LCE, most of the models depict overestimated El Niño signals and misrepresented the WNP anticyclone structure, which is not favourable for the development of IPOC mode and relationship with ISM rainfall. It is found that the models in which El Niño signals are overestimated, display a weak IPOC mode and IPOC-ISM relationship. Examining interannual and decadal changes of IPOC mode in Coupled General Circulation Models would be useful for a predictive understanding of monsoon variability and the associated contributing factors other than El Niño.