能動型衛星プロダクトを用いた北半球中高緯度におけるダストエアロゾル量と雲の熱力学的相の関係

抄録

To examine the relationship between the dust aerosol load and cloud thermodynamic phase, the fraction of ice phase (FIP) at the cloud top was analyzed using space-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) products in the summer (JJA) and winter (DJF) for one year. The target regions were east Eurasia (90˚E-130˚E, 40˚N-65˚N) and a part of America (70˚W-110˚W, 40˚N-65˚N). Unlike previous studies, we used the extinction coefficient (σ) as a more quantitative indicator of the dust aerosol load than relative frequency. Values of σ were larger in east Eurasia than in America, and the FIP between 250 K and 260 K was also approximately 20 % higher in east Eurasia than in America. As Kawamoto et al. (2020) point out, the difference in FIP would depend on the difference in σ. This means that FIP would be determined not only by temperature but also by σ. Next we compared FIPs in the two regions under consideration under the same temperature and σ conditions, and found again that FIP was considerably higher in east Eurasia than in America. There are two possible reasons for this phenomenon. First, dust aerosols might have different ice nucleating abilities depending on their locations of origin and chemical components, even if the aerosols are classified into the same ‘dust’ category by the satellite algorithm. The second explanation is that the analyzed sites might also contain other types of aerosols that could serve as ice nuclei, thereby changing the overall ice nucleating ability together with the dust aerosols. In-situ observations are required to investigate these reasons in detail, however. The present results will contribute to achieving more accurate climate model simulations by incorporating a more realistic relationship between σ and FIP.