Wintertime/summertime contrasts of cloud condensation nuclei and cloud microphysics over the Southern Ocean
Wintertime/summertime contrasts of cloud condensation nuclei and cloud microphysics over the Southern Ocean
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DOI：
10.1029/2003jd003864
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发表时间：
2004-03
影响因子：
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通讯作者：
S. Yum;J. Hudson
中科院分区：
文献类型：
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作者：
S. Yum;J. Hudson
[1]本文介绍了南大洋云实验中在澳大利亚塔斯马尼亚西海岸外的清洁海洋环境中观测到的云凝结核（CCN）和云微物理的冬夏对比。在1%的过饱和度（S）下，冬季的平均CCN浓度（NCCN）为32 cm−3，但如果只考虑基线（人为影响最小的海洋气流）飞行，则为19 cm−3。相比之下，夏季NCCN的平均值比冬季高出5倍以上。当只考虑基线飞行时，季节性对比更大，特别是在较低的S：夏季比冬季高出一个数量级，S低于0.1%。相应的云滴浓度（Nc）显示出类似的对比，但程度较小。夏季平均云滴浓度[Nc（ave）]仅比冬季浓度高2.5倍（70 cm−3对28 cm−3）。当只考虑基线飞行时，这一差异几乎是3倍（57 cm−3对20 cm−3）。飞行平均NCCN和绝热云滴浓度（Na）的各种表示一般表现出良好的相关性，表明CCN的原始效果在某种程度上保留在Nc（ave）。夏季和冬季云滴的平均直径分别为13.9和17.1 μm。仅基线时，平均MD分别为15.4和18.2 μm。因此，平均MD高于或接近15 μm的毛毛雨产生阈值，除了夏季的非基线云，其平均MD小于10 μm。由于较大的水滴尺寸，在冬季的云层中转化为毛毛雨的效率更高，平均毛毛雨液态水含量（Ld）为0.12 g m−3，是夏季Ld的两倍。夏季非基线云的Ld可以忽略不计。平均Ld也高度依赖于云的深度。冬季基线云有时太薄，即使它们包含非常低的Nc和非常大的MD，也不能产生显著的毛毛雨。最厚的云包含最高的Ld，虽然他们的MD并不总是最大的。
[1] Wintertime/summertime contrasts of cloud condensation nuclei (CCN) and cloud microphysics observed in clean maritime environments off the west coast of Tasmania, Australia in the Southern Ocean Cloud Experiment, are presented. The average wintertime CCN concentration (NCCN) was 32 cm−3 at 1% supersaturation (S), but it was 19 cm−3 when only baseline (maritime airflow with minimal anthropogenic influences) flights were considered. In contrast, the average summertime NCCN were more than a factor of 5 higher than wintertime for all S ranges. The seasonal contrast was larger when only baseline flights were considered, especially at lower S: summertime more than an order of magnitude higher than wintertime at S below 0.1%. Corresponding cloud droplet concentrations (Nc) showed similar contrasts but to a smaller extent. Summertime average cloud droplet concentrations [Nc(ave)] were only 2.5 times higher than wintertime concentrations (70 cm−3 versus 28 cm−3). This difference was nearly a factor of 3 when only baseline flights were considered (57 cm−3 versus 20 cm−3). Flight-average NCCN and various representations of adiabatic cloud droplet concentrations (Na) generally showed good correlations, indicating that the original effects of CCN are somehow retained in the Nc(ave). The average mean diameter (MD) of the cloud droplets was 13.9 and 17.1 μm for the summer and winter clouds, respectively. For baseline only, average MDs were 15.4 and 18.2 μm, respectively. Average MD was thus above or close to the 15-μm threshold for drizzle production, except for the summertime nonbaseline clouds, which had an average MD smaller than 10 μm. Because of the larger droplet sizes, conversion to drizzle was more efficient in the winter clouds, where the average drizzle liquid water content (Ld) of 0.12 g m−3 was twice that of the summer Ld. The Ld for the summer nonbaseline clouds was negligible. Average Ld was also highly dependent on cloud depth. Winter baseline clouds were sometimes too thin to produce significant drizzle even though they contained very low Nc and very large MDs. The thickest clouds contained the highest Ld although their MD was not always the largest.