Planetary Boundary Layer height over the Indian subcontinent during extreme monsoon years

Planetary Boundary Layer (PBL) plays an important role in the regional monsoon circulation by exchanging heat and moisture between the earth surface and free atmosphere. However, PBL climatology over the Indian sub-continent in the context of extreme monsoon conditions is not available for its use in the regional climate models. In this study, a large-scale seasonal feature of PBL height over the Indian sub-continent is explored with 40 years (1961–2000) ERA-40 reanalysis data. The variations in the PBL height associated with excess and deficient monsoons over India are examined. The seasonal climatology showed higher PBL height during pre-monsoon (spring) and monsoon seasons as compared to post-monsoon and winter. For the extreme monsoon situations, PBL over the north-west (NW) India has greatly reciprocated. Over the NW India, during deficient monsoon years, composite anomalies of the PBL are observed to be negative indicating large reduction in PBL. Whereas during excess monsoon years, observed positive anomalies suggest increase in the PBL. During excess (deficient) monsoon years, the convection and the LLJ are found to be stronger (weaker) associated with the higher (lower) PBL height.

► PBL over India in excess and deficient monsoon years were investigated.
► Over the NW India, during deficient monsoon years, the PBL height reduced greatly.
► Over the NW India, during excess monsoon years, the PBL height increased greatly.
► Convection and LLJ played a crucial role with PBL height over the NW India.