Vertical structure of atmospheric boundary layer over Ranchi during the summer monsoon season

Thermodynamic structure and variability in the atmospheric boundary layer have been investigated with the help of balloon-borne GPS radiosonde over a monsoon trough station Ranchi (Lat. 23°45′N, Long. 85°43′E, India) during the summer monsoon season (June–September) for a period of 2011–2013. Virtual potential temperature gradient method is used for the determination of mixed layer height (MLH). The MLH has been found to vary in the range of 1000–1300 m during the onset, 600–900 m during the active and 1400–1750 m during the break phase of monsoon over this region. Inter-annual variations noticed in MLH could be associated with inter-annual variability in convection and rainfall prevailing over the region. Along with the MLH, the cloud layer heights are also derived from the thermodynamic profiles for the onset, active and break phases of monsoon. Cloud layer height varied a lot during different phases of the monsoon. For the determination of boundary-layer convection, thermodynamic parameter difference (δθ = θes− θe) between saturated equivalent potential temperature (θes) and equivalent potential temperature (θe) is used. It is a good indicator of convection and indicates the intense and suppressed convection during different phases of monsoon.