Convective boundary layer information revealed by the lower atmospheric wind profiler over Gadanki, India

Abstract

A technique for determining the height of the convective atmospheric boundary layer (CBL) with lower atmospheric wind profiler (LAWP) at Gadanki is discussed. The results are qualitatively compared with simultaneous radiosonde observations. Gadanki-LAWP provides continuous CBL height measurements with very good time resolution (5 minutes or

less), allowing for detailed understanding of growth and fluctuations of CBL. During dry season, on clear days, a thin enhanced echo layer corresponding to the top of planetary boundary layer (PBL) appeared at about 500 m height in the morning and ascended to about 1500 m in the afternoon. Strong upward/downward velocities were observed below the echo

layer (or inside PBL), reaching 1.5 km in the afternoon. Two types of strong echo structures were found to appear systematically in the tropical PBL with diurnal variations on clear days during wet season. The first type, the striking appearance of an echo layer ascending from below 300 m (in the morning) to above 3-5 km (in the afternoon), was identified as a diurnal variation of the top of the mixing PBL. Another type is an elevated layer echo appearing at 2-3 km height from almost all the times, which seems to be coincided with humidity gradient. It is found, with a few exceptions, that the drier period had higher boundary layer than the wet period indicating that most of the net solar radiation evaporated the moisture rather than heating the surface, and therefore contributed a little to buoyant force.