Abstract
A shipborne micro-pulse lidar (Sigma Space Mini-MPL) was used to measure aerosol extinction coefficient over the northern region of the South China Sea from 9 August to 7 September 2016, the first time a mini-MPL was used for aerosol observation over the cruise region. The goal of the experiment was to investigate if the compact and affordable mini-MPL was usable for aerosol observation over this region. The measurements were used to calculate vertical profiles of volume extinction coefficient, depolarization ratio, and atmospheric boundary layer height. Aerosol optical depth (AOD) was lower over the southwest side of the cruise region, compared to the northeast side. Most attenuation occurred below 3.5 km, and maximum extinction values over coastal areas were generally about double of values offshore. The extinction coefficients at 532 nm (aerosol and molecular combined) over coastal and offshore areas were on average 0.04 km−1 and 0.02 km−1, respectively. Maximum values reached 0.2 km−1 and 0.14 km−1, respectively. Vertical profiles and back-trajectory calculations indicated vertical and horizontal layering of aerosols from different terrestrial sources. The mean volume depolarization ratio of the aerosols along the cruise was 0.04. The mean atmospheric boundary layer height along the cruise was 653 m, with a diurnal cycle reaching its mean maximum of 1041 m at 12:00 local time, and its mean minimum of 450 m at 20:00 local time. Unfortunately, only 11% of the measurements were usable. This was due to ship instability in rough cruise conditions, lack of stabilization rig, water condensation attached to the eye lens, and high humidity attenuating the echo signal. We recommend against the use of the mini-MPL in this cruise region unless substantial improvements are made to the default setup, e.g., instrument stabilization, instrument protection cover, and more theoretical work taking into account atmospheric gas scattering or absorption.
Highlights
Aerosols play an important role in the constitution of the troposphere
Note that the number of usable measurements differed for each section (Figure 1) and all the signals chosen were during sunny day in order to remove the effect of clouds and other complicated synoptic situations, and all profiles with low cloud have been removed by visual inspection, practically it was impossible to exclude all interfering situations
The pre-processing software had carried out some overlap correction with usable signals beginning from 255 m, the profiles of high extinction coefficients near the surface suggest that the correction could be improved
Summary
Aerosols play an important role in the constitution of the troposphere. Due to their effectiveness in absorbing and scattering solar radiation, aerosols can alter atmospheric temperature stratification and planetary albedo. Changes in aerosol distributions can change the Earth’s energy balance to alter regional and global climates [1,2,3,4,5]. The study of marine aerosols began later compared to that of terrestrial aerosols, due to limitation by technology and instruments. Marine aerosol research has developed rapidly in recent years with the advancement of technology [8,9,10,11,12]
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