NOPR Collection:

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

2003-10-01T00:00:00Z

Title: Convective boundary layer information revealed by the lower atmospheric wind profiler over Gadanki, India Authors: Reddy, K Krishna 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. Page(s): 312-319

Atmospheric aerosols and air pollution

2003-10-01T00:00:00Z

Title: Atmospheric aerosols and air pollution Authors: Raju, N V; Prasad, B S N; Narasimhamurthy, B Abstract: Multiwavelength radiometer measurement of aerosol optical depth (AOD) at ten wavelengths in the visible and near IR is an ongoing programme since 1988 at Mysore (12°N, 76°E), a semi-urban continental area with a population of about 1 million. The analysis of 10-yr data indicates an increase in the spectral AOD which is attributed to the increased air pollution resulting from anthropogenic activities. The pollution related aerosol turbidity parameters α and β are determined graphically from AOD. The size-dependent parameter α shows a decrease initially and later on an increase. The number density parameter β remains almost a constant throughout the data period. Aerosol size spectrum is retrieved by numerically inverting the AODs, and the aerosol characteristics are estimated. These indicate that a depends on the number of accumulation mode particles, and β on the mass loading. Page(s): 306-311

Column density of atmospheric water vapour over Ahmedabad

2003-10-01T00:00:00Z

Title: Column density of atmospheric water vapour over Ahmedabad Authors: Chakrabarty, D K; Patel, S; Vala, P; Iyer, K N Abstract: Water vapour spectrum has a strong absorption feature around 442.7 nm. Using this property column density of water vapour has been determined at Ahmedabad, a low latitude station. Measurements have been made from 1996 to 2000. Slant column density has been found to be ~10²⁴ cm^-2. The period stretches from a minimum to maximum solar activity. A decreasing trend of water vapour content with an increase of solar activity level is also seen. Page(s): 301-305

Rain drop size distribution from radar reflectivity measurements

2003-10-01T00:00:00Z

Title: Rain drop size distribution from radar reflectivity measurements Authors: Mali, P; Sarkar, S K; Das, J Abstract: Rain drop size distribution (RDSD) is useful for estimation of attenuation of high frequency electromagnetic waves due to rain. In this paper, radar reflectivity (Z) obtained by using an X-band radar operating at ~9.4 GHz has been used for deducing the results on RDSD at different rain intensities in the range 50-150 mm/hr. The present results have been observed to match with the results obtained by other investigators by using distrometers for the same range of rain rates. The equation obtained for RDSD is of general type and it would satisfy RDSD for the other rain rates also, if the radar reflectivity (Z) is calibrated properly with various rain rates. The unique feature of this distribution equation has its direct application in radar reflectivity data and rain rate for RDSD. Page(s): 296-300