Lidar profiling of aerosol scavenging parameters at a tropical station, Pune, India

Abstract

In this study, we deal with observations of aerosol column content (height integration of vertical distribution of aerosol number density) that have been carried out using an Ar⁺ lidar for three different measurement cycles (each cycle consisting of three experimental days associated with non-rain, rain, and non-rain, respectively) of weekly spaced observations for pre-monsoon (March/April 1994), monsoon (September 1991), and post-monsoon (October 1998). Based on these observed profiles of aerosol number concentration on rainy days with respect to those on non-rainy days, vertical distributions of scavenging collection efficiencies (SCEs) are computed and discussed in this article. The SCE is found to decrease from 0.3 to 0.01 between the heights, 100 and 800 m for thunderstorm rain in April 1994, and during monsoon, it increases from 0.1 to 0.7. In the October 1998 episode, SCE was found to increase initially from 0.35 to 0.75 for heights between 40 and 200 m and thereafter decrease to 0.35 in the height interval of 200–800 m. For the rainfall intensity increase from 1 to 10 mm hour⁻¹, the corresponding scavenging coefficient (SC) for atmospheric layer 50–100 m varies from 4 × 10⁻⁶ to 4 × 10⁻⁵ s⁻¹ for thunderstorm in April 1994 and between 5 × 10⁻⁶ and 5 × 10⁻⁵ s⁻¹ in October 1998, respectively. During monsoon, these values vary from 3 × 10⁻⁵ to 5 × 10⁻⁴ s⁻¹. They lie in the range of those observed in the earlier field studies. The results are found useful to establish links between aerosols and cloud properties, and the influence of such interactions on weather and climate.

Acknowledgements

The authors are thankful to the editor and anonymous reviewers for their valuable comments that improved the scientific content and clarity of the article.

Funding

The Indian Institute of Tropical Meteorology (IITM), Pune, India, is completely funded by the Ministry of Earth Sciences (MoES), Government of India, New Delhi. The authors sincerely acknowledge the support from Director, IITM, and cooperation from all Members of the ‘Aerosols and Cloud Physics Laboratory for Weather and Climate Studies’.