Planetary boundary layer height by means of lidar and numerical simulations over New Delhi, India

Konstantina Nakoudi,Maria Tombrou,Mika Komppula,Aggeliki Dandou,Elina Giannakaki

doi:10.5194/amt-12-2595-2019

Abstract

Abstract. In this work, the height of the planetary boundary layer (PBLH) is investigated over Gwal Pahari (Gual Pahari), New Delhi, for almost a year. To this end, ground-based measurements from a multiwavelength Raman lidar were used. The modified wavelet covariance transform (WCT) method was utilized for PBLH retrievals. Results were compared to data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and the Weather Research and Forecasting (WRF) model. In order to examine the difficulties of PBLH detection from lidar, we analyzed three cases of PBLH diurnal evolution under different meteorological and aerosol load conditions. In the presence of multiple aerosol layers, the employed algorithm exhibited high efficiency (r=0.9) in the attribution of PBLH, whereas weak aerosol gradients induced high variability in the PBLH. A sensitivity analysis corroborated the stability of the utilized methodology. The comparison with CALIPSO observations yielded satisfying results (r=0.8), with CALIPSO slightly overestimating the PBLH. Due to the relatively warmer and drier winter and, correspondingly, colder and rainier pre-monsoon season, the seasonal PBLH cycle during the measurement period was slightly weaker than the cycle expected from long-term climate records.

Highlights

The planetary boundary layer (PBL) is the lowermost portion of the troposphere, which experiences a diurnal cycle of temperature, humidity, wind and pollution variations
1-year-long ground-based lidar measurements were used to retrieve the PBLH over Gwal Pahari, New Delhi
The feasibility of deriving the PBLH with the modified wavelet covariance transform (WCT) technique was investigated and the respective results were compared to independent sources

Summary

Introduction

The planetary boundary layer (PBL) is the lowermost portion of the troposphere, which experiences a diurnal cycle of temperature, humidity, wind and pollution variations. The PBL height (PBLH) is the most adequate parameter to represent the PBL. It is usually required in numerous applications, for instance in pollution-dispersion modeling, where the upper boundary of the turbulent layer acts as an impenetrable lid for the pollutants emitted at the surface. The PBLH appears as a mixing-scale height in turbulence closure schemes within climate and weather prediction models (Zilitinkevich and Baklanov, 2001). Several methods have been proposed to estimate the PBLH, utilizing vertically resolved thermodynamic variables, turbulence-related parameters and concentrations of tracers (Seibert et al, 2000; Emeis et al, 2004).

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