Preferred intra-seasonal circulation patterns of the Indian summer monsoon and active-break cycles

Intra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean anomaly fields of 850 hPa horizontal winds from the ERA-Interim reanalysis for the boreal summer season (June–Sept. for 1979–2018) over the region (50°–100° E; 5° S–35° N). The k-means method was applied to the leading 6 principal components yielding k clusters. The degree of clustering is significant compared to synthetic data sets for any value of k > 3 . The circulation is most likely to stay in the same cluster from one pentad to the next; significant transitions (with 95