Evaluation of the boundary layer depth in semi-arid region of India

The annual variation in Planetary Boundary Layer (PBL) height is determined from the profiles of conserved thermodynamic variables, i.e. virtual potential temperature θv, equivalent potential temperature θe and saturated equivalent potential temperature θes, using radiosonde data at Anand (23°35′N, 72°55′E, 45.1 m a.s.l.), India. Out of all the variables, the θv profile seems to provide the most reasonable estimate of the PBL height. This has been supplemented by T–Phi gram analysis for specific days. The analysis has been done for 00, 03, 06, 09 and 12 GMT for the 14th and 15th day of each month in the year 1997 based on LASPEX-97 data. In winters the height of boundary layer is very low due to subsidence and radiation cooling while heights in pre-monsoon months exhibit large variations.