Possible mechanism for change in rainfall. Anomalous geopotential height at 200hPa during (a) break, transition (break-active), and active phases in the CE. (b) Same as (a) but for HE–CE, showing the change in HE compared to CE. Change in vertical wind shear (U
) averaged over the northern Indian region (20°N to 35°N and 65°E to 95°E) in different phases (break, transition (break-to-active), active, and transition (active-to-break), respectively) from (c) Model and (d) Observations. Change in VMS over the CI region in different phases from (e) Model and (f) Observations. Observational analysis here is done using NCEP-NCAR Reanalysis-135 data. Trend in global mean temperature is subtracted before calculating VMS. Units are in m for geopotential height, m/s for wind shear, and kJ/kg for VMS. Dotted regions in (b) and asterisks in (c–f) indicate where the changes are significant at 10% level (using t-test). ‘A’ and ‘C’ in (a) and (b) indicate the anticyclonic and cyclonic structures of winds at upper troposphere, respectively. Figures are generated using NCAR Command Language 6.3.0 (http://www.ncl.ucar.edu/).