Comparison of backscatter coefficient at 1064nm from CALIPSO and ground-based ceilometers over coastal and non-coastal regions

Thaize Baroni,Colin O'Dowd,Jana Preissler,Gary Gimmestad,Praveen Pandey,Upendra N Singh,Evgueni I Kassianov,Adolfo Comerón,Richard H Picard,Klaus Schäfer,Konradin Weber

doi:10.1117/12.2573064

Abstract

This pilot study investigates the direct comparison of backscatter coefficient profiles at 1064 nm which were measured by CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) and by a ground-based ceilometer located at the west coast of Ireland. Data recorded between 2013 to 2016 is used to investigate the challenges and limitations in performing such a comparison. The standard Level 2 CALIOP Aerosol Profile version 4 product is compared to data from a ground-based Jenoptik CHM15K ceilometer. A statistical analysis considering CALIOP overpasses within 100 km from the ceilometer is presented taking into account different along-track averages in CALIOP data (5 km, 15 km, 25 km, 35 km and 100 km) at the closest approach. The mean bias calculated from the correlative measurements between CALIOP and the ground-based ceilometer at Mace Head for cloud-free scenarios shows negative bias for 80% of the cases. The comparison of these results with HYSPLIT shows that air samples with higher or lesser content of marine aerosols produced different biases between the measurements. To our knowledge, this is the first study that investigates the limitations and capabilities in comparing CALIOP and ground-based ceilometer measurements using the 1064 nm wavelength.

Highlights

Aerosol scattering and absorbing properties have a direct impact on the global radiative budget and an indirect impact on cloud formation and microphysics [1]
In order to demonstrate the methodology described in the previous section, two particular cases are discussed for Mace Head, Ireland and two for Harzgerode, Germany
53 CALIPSO overpasses occurred within a 100 km ground track offset distance from an operating ceilometer in the coastal site of Mace Head, Ireland, and 50 occurred from the non–coastal site of Harzgerode, Germany

Summary

Introduction

Aerosol scattering and absorbing properties have a direct impact on the global radiative budget and an indirect impact on cloud formation and microphysics [1]. The tropospheric aerosols possess a substantial spatial and temporal variability, which leads to significant uncertainties in the estimation of radiative forcing in climate change studies [2]. The aerosol radiative forcing has a strong dependence on its vertical distribution. On the other hand, exhibit a more significant forcing when their mass is above cloud layers [3]. A better understanding of aerosol vertical (and horizontal) distribution and lifetime in the atmosphere is essential to investigate climate change and to improve forecast and dispersion models [4]. Aerosol and cloud properties can be observed either by in–situ or remote sensing instruments.

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