The role of natural factors (part 2): Indian summer monsoon in climate change period—observation and CMIP5 models

This study discusses the role of natural factors and related teleconnections for Indian summer monsoon (ISM) with a special emphasis on later two decades of the last century. The combined influence of the sun and volcanos on ISM is examined using observational data as well as CMIP5 model outputs. Possible mechanisms relating to a disruption of the usual ENSO-ISM teleconnection for those decades are explored. Observation suggested that the regional Hadley circulation, via the NAO in the northern hemisphere and Indian Ocean Dipole in the southern hemisphere, may have a role in the change in ISM behaviour. Such features though captured well in the observation are shown missing in models. Additionally, it indicates that differences among models mainly originate in a regional level, which could be due to inconsistency in representing regional teleconnection features. Interestingly, all models perform reasonably well in terms of global thermodynamic scaling arguments. The overall study underpins important areas, where natural factors influence regional climate, but models miss out and suggest discrepancies among each other. Such knowledge has major implications in regional as well as global scale. The modelling community will also greatly benefit by an improved representation of ENSO and ISM in models.