Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations
Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations
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DOI：
10.5194/acp-14-13223-2014
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发表时间：
2014-12
影响因子：
6.3
通讯作者：
W. Frey;S. Borrmann;F. Fierli;R. Weigel;V. Mitev;R. Matthey;F. Ravegnani;N. Sitnikov;A. Ulanovsky;F. Cairo
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文献类型：
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作者：
W. Frey;S. Borrmann;F. Fierli;R. Weigel;V. Mitev;R. Matthey;F. Ravegnani;N. Sitnikov;A. Ulanovsky;F. Cairo
抽象的。这里介绍的案例研究重点关注热带深对流系统砧区云的生命周期。在澳大利亚北部达尔文的 SCOUT-O3 活动期间，地球物理高空飞机对赫克托风暴系统进行了探测。通过原位粒子探测器、反向散射探空仪和微型激光雷达来观察云。此外，还测量了气溶胶数量浓度。 2005 年 11 月 30 日，发生了一次双重飞行，赫克托在其发育、成熟和消散阶段的整个生命周期都受到了探测。两次飞行相隔 4 小时，重点关注海拔 10.5 至 18.8 公里之间的赫克托砧区（即潜在温度高于 350 K）。使用轨迹计算、卫星图像和臭氧测量来确保两次飞行探测到相同的云气团。测量得出的尺寸分布不仅随着海拔的增加而变化，而且随着赫克托的演化而变化。在赫克托的不同发展阶段，发现了明显不同的云与气溶胶颗粒比例以及不同的冰晶形态，表明了不同的冻结机制。发育阶段呈现出最小的冰颗粒（最大300微米），且形态相当均匀。这表明赫克托发育期间发生了快速的冰川作用。成熟阶段的冰晶尺寸最大（大于1.6毫米），甚至超过了一些大陆热带深对流云，数量浓度也是如此。反向散射特性和颗粒图像显示冰晶形状从发展阶段到成熟和消散阶段的边缘和聚集颗粒的变化；无法从测量中区分出发展阶段颗粒的具体形状。尽管光学上很薄，但消散阶段的云具有很大的垂直范围（大约 6 公里）并持续至少 6 小时。因此，这些到达高度的深对流云的砧极有可能通过改变湿度和辐射预算来影响热带对流层顶层，并为看不见的卷云的形成提供有利的条件。所涉及的过程还可能影响最终到达热带平流层的水蒸气量。
Abstract. The case study presented here focuses on the life cycle of clouds in the anvil region of a tropical deep convective system. During the SCOUT-O3 campaign from Darwin, Northern Australia, the Hector storm system has been probed by the Geophysica high-altitude aircraft. Clouds were observed by in situ particle probes, a backscatter sonde, and a miniature lidar. Additionally, aerosol number concentrations have been measured. On 30 November 2005 a double flight took place and Hector was probed throughout its life cycle in its developing, mature, and dissipating stage. The two flights were four hours apart and focused on the anvil region of Hector in altitudes between 10.5 and 18.8 km (i.e. above 350 K potential temperature). Trajectory calculations, satellite imagery, and ozone measurements have been used to ensure that the same cloud air masses have been probed in both flights. The size distributions derived from the measurements show a change not only with increasing altitude but also with the evolution of Hector. Clearly different cloud to aerosol particle ratios as well as varying ice crystal morphology have been found for the different development stages of Hector, indicating different freezing mechanisms. The development phase exhibits the smallest ice particles (up to 300 μm) with a rather uniform morphology. This is indicative for rapid glaciation during Hector's development. Sizes of ice crystals are largest in the mature stage (larger than 1.6 mm) and even exceed those of some continental tropical deep convective clouds, also in their number concentrations. The backscatter properties and particle images show a change in ice crystal shape from the developing phase to rimed and aggregated particles in the mature and dissipating stages; the specific shape of particles in the developing phase cannot be distinguished from the measurements. Although optically thin, the clouds in the dissipating stage have a large vertical extent (roughly 6 km) and persist for at least 6 h. Thus, the anvils of these high-reaching deep convective clouds have a high potential for affecting the tropical tropopause layer by modifying the humidity and radiative budget, as well as for providing favourable conditions for subvisible cirrus formation. The involved processes may also influence the amount of water vapour that ultimately reaches the stratosphere in the tropics.