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[ACC26-08] The correlations between cloud amount over Northern mid-high latitudes and aerosol proxies preserved in the SE-Dome ice core, Greenland
Keywords:SE-Dome ice core, sulfate ion flux, cloud amount, correlation coefficient, North Atlantic Ocean
The SE-Dome Ice Core(SE-Core), drilled out from a high elevation and accumulation area, preserves paleoenvironmental proxies such as aerosols of the last 60 years with a high time resolution(±2month) 1). Past aerosols in the SE-Core mainly came from North Atlantic Ocean and North America1). Although many papers suggested that aerosols act as cloud condensation nuclei (CNN)2)3), the relationships between past cloud amount and aerosols in ice cores are not well understood yet. If past aerosols preserved in ice cores can be a proxy of past cloud amount, that would help better understand the fluctuation mechanism of aerosol-cloud interactions than ever before.
To examine the relationships between cloud amount over Northern mid-high latitudes and the aerosol proxies preserved in the SE-Core, we used the cloud amount data sets from satellite and reanalysis of Ⅰ) Advanced Very High Resolution Radiometer(AVHRR), Ⅱ) International satellite cloud climatology project(ISCCP), and Ⅲ) ERA5 products provided by European Centre for medium-range weather forecasts(ECMWF) from 1979 to 2014.We calculated cloud-aerosol correlation coefficients at a resolution of 2.5°latitude by 2.5°longitude over Northern mid-high latitudes.We use 15 aerosol proxies from the SE-Core(calcium ion, sulfate ion, and so on)4) and cloud amount divided into 4 types (low, middle, high, and total levels) of the 3 data sets for 6 types of season or annual{Winter(DJF), Spring(MAM), Summer(JJA), Autumn(SON), Spring-Summer(AMJJAS), and Autumn-Winter(ONDJFM)}. Thus, the combination amounts to 1,260 cases (15×4×3×7) for the correlation coefficient.
Among the 1,260 cases, the correlation coefficients between total and low-levels cloud amount, and sulfate ion flux in North America(75°W - 100°W,45°N - 70°N) and North Atlantic Ocean (20°W - 50°W,45°N - 60°N) are significantly high (R > 0.329) in all the 3 data sets. The sulfate ion in the SE-Core mainly originates from anthropogenic SO2 in North America and biologic SO2 in the North Atlantic5). The significant correlations suggest that sulfate aerosols may contribute to increasing cloud amount in the emission area. We also examined the correlation coefficients between sulfate ion flux and cloud amount under fixed conditions on relative humidity, temperature and surface pressure, which are considered as main factors of clouds formation. For example, we analyzed the correlation coefficients between sulfate ion flux and total cloud amount in AMJJAS when the relative humidity variability in North Atlantic Ocean was within 1 standard deviation from 1979 to 2014. The correlation coefficients were significantly high (R > 0.496) in North Atlantic Ocean. Thus, the correlation coefficients between cloud amount and sulfate ion flux preserved in the SE-Core are significant even under the same condition of the main factors of clouds formation.
It is suggested that sulfate aerosols contribute to an increase of cloud amount in the process of acting as a CCN.
References
1)Iizuka et al, J. Geo.Res.Atm., 123, 1, 574–589,2018
2)Fan et al, J. Atmos. Sci.,73,4221-4250,2016
3)Stevens and Feinhgold, Nature, 10,461,7264,2009
4)Amino et al, Polar Sci.,10,2020
5)Furukawa et al, J. Geo.Res.Atm., 122, 10,873–887,2017A
To examine the relationships between cloud amount over Northern mid-high latitudes and the aerosol proxies preserved in the SE-Core, we used the cloud amount data sets from satellite and reanalysis of Ⅰ) Advanced Very High Resolution Radiometer(AVHRR), Ⅱ) International satellite cloud climatology project(ISCCP), and Ⅲ) ERA5 products provided by European Centre for medium-range weather forecasts(ECMWF) from 1979 to 2014.We calculated cloud-aerosol correlation coefficients at a resolution of 2.5°latitude by 2.5°longitude over Northern mid-high latitudes.We use 15 aerosol proxies from the SE-Core(calcium ion, sulfate ion, and so on)4) and cloud amount divided into 4 types (low, middle, high, and total levels) of the 3 data sets for 6 types of season or annual{Winter(DJF), Spring(MAM), Summer(JJA), Autumn(SON), Spring-Summer(AMJJAS), and Autumn-Winter(ONDJFM)}. Thus, the combination amounts to 1,260 cases (15×4×3×7) for the correlation coefficient.
Among the 1,260 cases, the correlation coefficients between total and low-levels cloud amount, and sulfate ion flux in North America(75°W - 100°W,45°N - 70°N) and North Atlantic Ocean (20°W - 50°W,45°N - 60°N) are significantly high (R > 0.329) in all the 3 data sets. The sulfate ion in the SE-Core mainly originates from anthropogenic SO2 in North America and biologic SO2 in the North Atlantic5). The significant correlations suggest that sulfate aerosols may contribute to increasing cloud amount in the emission area. We also examined the correlation coefficients between sulfate ion flux and cloud amount under fixed conditions on relative humidity, temperature and surface pressure, which are considered as main factors of clouds formation. For example, we analyzed the correlation coefficients between sulfate ion flux and total cloud amount in AMJJAS when the relative humidity variability in North Atlantic Ocean was within 1 standard deviation from 1979 to 2014. The correlation coefficients were significantly high (R > 0.496) in North Atlantic Ocean. Thus, the correlation coefficients between cloud amount and sulfate ion flux preserved in the SE-Core are significant even under the same condition of the main factors of clouds formation.
It is suggested that sulfate aerosols contribute to an increase of cloud amount in the process of acting as a CCN.
References
1)Iizuka et al, J. Geo.Res.Atm., 123, 1, 574–589,2018
2)Fan et al, J. Atmos. Sci.,73,4221-4250,2016
3)Stevens and Feinhgold, Nature, 10,461,7264,2009
4)Amino et al, Polar Sci.,10,2020
5)Furukawa et al, J. Geo.Res.Atm., 122, 10,873–887,2017A