Observational relations between potential vorticity intrusions and pre-monsoon rainfall over Indian sector

The climatology of potential vorticity (PV) intrusion events to low latitudes, identified from the ECMWF (European Centre for Medium Range Weather Forecasting) reanalysis (ERA) interim data for the years 1982–2012, shows that the intrusion events occur, though less in number, over African and Indian sectors (0°–90°E) also, in addition to the well known intrusions over Eastern Pacific and Atlantic sectors. The seasonal variation of the PV intrusion events over Indian sector (50°E–90°E) shows that the intrusion events are more during pre-monsoon months, in particular during March and April contrary to the case over Eastern Pacific and Atlantic sectors, where the intrusions are more during winter. It is interesting to note that no intrusion events occur during the Indian monsoon months (June–September) due probably to the presence of tropical easterly jet. Though the number of PV intrusions is less, it plays a profound role in triggering deep convection and associated precipitation over Indian sector. Four cases are presented to show that these PV intrusions are clearly associated with deep convection and precipitation over Indian sector during the pre-monsoon months.