Measurements of regional-scale aerosol impacts on cloud microphysics over the East China Sea: Possible influences of warm sea surface temperature over the Kuroshio ocean current
Measurements of regional-scale aerosol impacts on cloud microphysics over the East China Sea: Possible influences of warm sea surface temperature over the Kuroshio ocean current
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DOI：
10.1029/2011jd017324
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发表时间：
2012-09-11
影响因子：
4.4
通讯作者：
Nakajima, T. Y.
中科院分区：
文献类型：
--
作者：
Koike, M.;Takegawa, N.;Nakajima, T. Y.
2009年4月，在“东亚气溶胶辐射强迫”（A-FORCE）试验中，利用飞机对东海和黄海上空的云微物理特征和气溶胶浓度进行了测量。我们在距中国大陆东海岸500-900公里的海面上进行了7次共9次的层积云和浅积云采样。在这项研究中，我们报告气溶胶对云微物理特性的影响，重点是两个关键参数，即上升气流速度和气溶胶粒径分布的区域特征。首先，我们发现云滴数浓度（最高5%，N-c_（max））与云下累积型气溶胶数浓度（N-a）有很好的相关性。然后，我们表明，Nc_max部分相关的近地面层结评估之间的差异海表温度（SST）和950百帕温度（SST - T-950）。从中国到东海的冷空气平流不仅带来了大量的气溶胶，而且还带来了干燥和冷的空气团，使大气边界层不稳定，特别是在温暖的黑潮洋流上方。在这个高SST区，可能导致更大的上升气流速度，从而导致更大的N-c_（max）。我们假设由SST和区域尺度气流确定的低层静稳定度调制云的微物理（气溶胶对云的影响）和宏观结构（云底和云顶高度，因此云液态水路径）。第二，我们表明，不仅较高的气溶胶负载的总气溶胶数浓度（N-CN，D > 10 nm），而且更大的气溶胶模式直径可能有助于高N-c在A-FORCE。平均Nc为650 +/- 240 cm（-3），比受大陆来源影响的云的全球平均值大2倍以上。对气溶胶引起的云辐射强迫也作了粗略的估计。
Cloud microphysical properties and aerosol concentrations were measured aboard an aircraft over the East China Sea and Yellow Sea in April 2009 during the Aerosol Radiative Forcing in East Asia (A-FORCE) experiment. We sampled stratocumulus and shallow cumulus clouds over the ocean in 9 cases during 7 flights 500-900 km off the east coast of Mainland China. In this study we report aerosol impacts on cloud microphysical properties by focusing on regional characteristics of two key parameters, namely updraft velocity and aerosol size distribution. First, we show that the cloud droplet number concentration (highest 5%, N-c_(max)) correlates well with the accumulation-mode aerosol number concentration (N-a) below the clouds. We then show that Nc_max correlates partly with near-surface stratification evaluated as the difference between the sea surface temperature (SST) and 950-hPa temperature (SST - T-950). Cold air advection from China to the East China Sea was found to bring not only a large number of aerosols but also a dry and cold air mass that destabilized the atmospheric boundary layer, especially over the warm Kuroshio ocean current. Over this high-SST region, greater updraft velocities and hence greater N-c_(max) likely resulted. We hypothesize that the low-level static stability determined by SST and regional-scale airflow modulates both the cloud microphysics (aerosol impact on clouds) and macro-structure of clouds (cloud base and top altitudes, hence cloud liquid water path). Second, we show that not only higher aerosol loading in terms of total aerosol number concentration (N-CN, D > 10 nm) but also larger aerosol mode diameters likely contributed to high N-c during A-FORCE. The mean Nc of 650 +/- 240 cm(- 3) was more than a factor of 2 larger than the global average for clouds influenced by continental sources. A crude estimate of the aerosol-induced cloud albedo radiative forcing is also given.