Zhejiang University: ZJU scientists delve into aerosol-cloud interaction using a new lidar technique

Aerosol-cloud interaction (ACI) is a crucial aspect of atmospheric research and one of the primary sources of uncertainties in climate predictions. However, our understanding of ACI, such as the ACI mechanisms in the climate models, the influence of aerosols on serving as cloud condensation nuclei to form water cloud droplet and the evolution of water clouds, is hampered by the inadequate observational capability. Therefore, there is an urgent need for high-quality and high-resolution observations to investigate ACI process.

At present ACI is complex and difficult to be well represented in current climate models. High-spectral-resolution lidar (HSRL) is a powerful tool for simultaneous profiling the optical properties of aerosols and clouds. Yet, further progress regarding lidar-based techniques for ACI studies is circumscribed by the difficulties in quantifying the multiple-scattering effect in water clouds. Employing dual field-of-views (FOVs) opens up the possibility for quantifying the multiple-scattering effect, allowing profiling of water cloud microphysical properties. The combination of HSRL and dual FOVs provides the new insights into the ACI study.

Recently, the research team led by Prof. LIU Dong and Prof. LIU Chong at the Zhejiang University College of Optical Science and Engineering published a research article entitled “Dual-field-of-view high-spectral-resolution lidar: simultaneous profiling of aerosol and water cloud to study aerosol-cloud interaction” in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Benefiting from the range-resolve observations of aerosols and clouds with high resolution using the dual-FOV HSRL system, the research team has collected massive data of aerosols and clouds in North China Plain. Besides, this system also served as the intercomparison system for the airborne prototype in the China’s first atmospheric lidar satellite mission ( called DQ-1) and provided accurate data for the validation of the airborne prototype.

Direct lateral observations of cloud properties show that the vertical structure of low-level water clouds can be far from being perfectly adiabatic, contradicting with the traditional thinking. Furthermore, by analyzing the ACI process the research team found that increased aerosol loading led to the increased droplet number concentration and the decreased droplet effective radius whereas there was no discernible increase in terms of liquid water path. This finding supports the hypothesis that aerosol-induced cloud water increase caused by suppressed rain formation can be canceled out by enhanced evaporation. It thus constitutes a substantial and significant addition to understanding the ACI process.

It is the first time that the dual-FOV HSRL technique has been reported and applied to the ACI research. This versatile system can not only benefit the quality monitoring of aerosol and cloud properties, but also serve as a powerful tool for ACI studies. This technique is expected to represent a significant step forward in charactering ACI.

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