Planetary Boundary Layer variability over New Delhi, India, during EUCAARI project

Abstract. Ground-based lidar measurements were performed at Gual Pahari measurement station, approximately 20 km South of New Delhi, India, from March 2008 to March 2009. The height of the Planetary Boundary Layer (PBL) was retrieved with a portable Raman lidar system, utilizing the modified Wavelet Covariance Transform (WCT) method. The lidar derived PBL heights were compared to radiosonde data, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite observations and two atmospheric models. The results were also analyzed on a seasonal basis. To examine the difficulties of PBL lidar detection under different meteorological and aerosol load conditions we focused on three case studies of PBL diurnal evolution. In the presence of a multiple aerosol layer structure, the WCT method exhibited high efficiency in PBL height determination. Good agreement with the European Center for Medium-range Weather Forecasts (ECMWF) and the Weather Research and Forecasting (WRF) estimations was found (r=0.69 and r=0.74, respectively) for a cumulus convection case. In the aforementioned cases, temperature, relative humidity and potential temperature radiosonde profiles were well compared to the respective WRF profiles. The Bulk Richardson Number scheme, which was applied to radiosonde profile data, was in good agreement with lidar data, especially during daytime (r=0.68). The overall comparison with CALIPSO satellite observations; namely, CALIOP Level 2 Aerosol Layer Product, was very satisfying (r=0.84), with CALIPSO Feature Detection Algorithms slightly overestimating PBL height. Lidar measurements revealed that the maximum PBL height was reached approximately three hours after the solar noon, whilst the daily evolution of the PBL was completed, on average, one hour earlier. The PBL diurnal cycle was also analyzed using ECMWF estimations, which produced a stronger cycle during the winter and pre-monsoon period. The seasonal analysis of lidar PBL heights yielded a less pronounced PBL cycle than the one expected from long term climate records. The lowest mean daytime PBL height (695 m) appeared in winter, while the highest mean daytime PBL height (1326 m) was found in the monsoon season as expected. PBL daily growth rates exhibited also a weak seasonal variability.