Simulated changes in active/break spells during the Indian summer monsoon due to enhanced CO2 concentrations: Assessment from selected coupled atmosphere - Ocean global climate models

The simulations by ten coupled GCMs under the Intergovernmental Panel on Climate Change Assessment Report-4 are used to study the implication of possible global climate change on active/break spells of the Indian summer monsoon (ISM). The validation of the mean daily cycle of the summer monsoon precipitation over the Indian core region and the spatial pattern of the ISM precipitation climatology with observation suggest that six models simulate fairly well, whereas four models differ from observation. Thus, the identification of active/break spells is confined to six models. The sensitivity to climate change has been assessed from two experiments, namely, 1 per year CO2 increase to doubling and 1 per year CO2 increase to quadrupling. The changes in the daily mean cycle and the standard deviation of precipitation, frequency, and duration of active/break spells in future climate change are uncertain among the models and at times among two experiments. The break composite precipitation anomalies strengthen and spread moderately (significantly) in the doubled (quadrupled) CO2 experiment