Characteristics of cirrus clouds in the tropical lower stratosphere
Characteristics of cirrus clouds in the tropical lower stratosphere
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DOI：
10.1016/j.atmosres.2015.06.009
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发表时间：
2015-10
影响因子：
5.5
通讯作者：
S. Iwasaki;Z. Luo;H. Kubota;T. Shibata;H. Okamoto;H. Ishimoto
中科院分区：
文献类型：
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作者：
S. Iwasaki;Z. Luo;H. Kubota;T. Shibata;H. Okamoto;H. Ishimoto
本研究描述了热带平流层下层的一种独特的云，我们称之为“平流层卷云”。平流层卷云通常脱离过冲的深层对流，比通常在热带对流层顶附近观测到的次视卷云小得多。利用正交偏振云-气溶胶激光雷达（CALIOP）对热带和亚热带低空平流层的两例平流层卷云进行了分析。这两种情况都发生在附近对流云团最活跃的阶段后2-3小时。案例1在冷点高度（CPH）以上具有双层结构；CPH和两个云顶高度分别为17.8、18.9和19.9 km。情形2为单云层，CPH为16.5 km，云顶高度为18.7 km。基于雷达-激光雷达方法，考虑云粒子终端速度，估计平流层卷云模式半径为4 ~ 10 μm，冰水含量为0.2 ~ 0.8 mg/m3。与先前数值模式模拟研究的比较表明，双层平流层卷云很可能来自超冲羽流，当平流层暖空气与超冲冷空气不均匀混合时，超冲羽流被推入平流层。单层平流层卷云与一些不可忽略的风切变有关，因此它可能是一个跳跃的卷云，但由于两种情况的云特征和形态相似，我们不能排除它来自超冲羽的可能性。在案例研究的指导下，开发了一种自动选择平流层卷云进行全球调查和统计分析的算法。总共分析了四年的CALIPSO和星载云雷达（CloudSat）数据。统计分析表明，在南纬30°~北纬30°之间，平流层卷云年出现次数约为3.0 × 103次。许多平流层卷云出现在南亚和东南亚的季风前季节，那里对流深而强烈。
A unique type of cloud in the tropical lower stratosphere, which we call “stratospheric cirrus”, is described in this study. Stratospheric cirrus clouds are generally detached from overshooting deep convection and are much smaller than subvisual cirrus often observed near the tropical tropopause. We analyzed two cases of stratospheric cirrus in the tropical and subtropical lower stratosphere captured by the space-borne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Both cases occurred 2–3 hours after the most active phase of the nearby convective cloud clusters. Case 1 has a double-layer structure above the cold point height (CPH); the CPH and two cloud top heights are, respectively, 17.8, 18.9, and 19.9 km. Case 2 has a single cloud layer where CPH and the cloud top height are, respectively, 16.5 and 18.7 km. The mode radius and ice water content of the stratospheric cirrus clouds are estimated to be 4–10 μm and 0.2–0.8 mg/m3based on the radar-lidar method and consideration of the cloud particle terminal velocity. Comparisons with previous numerical model simulation studies suggest that the double-layer stratospheric cirrus clouds are likely from an overshooting plume, pushed up into the stratosphere in an overshoot when warm stratospheric air is inhomogeneously mixed with cold overshooting air. The single-layer stratospheric cirrus cloud is associated with some non-negligible wind shear, so it could be a jumping cirrus cloud, although we cannot rule out the possibility that it came from an overshooting plume because of the similarity in cloud characteristics and morphology between the two cases. Guided by the case studies, an automatic algorithm was developed to select stratospheric cirrus clouds for global survey and statistical analysis. A total of four years of CALIPSO and space-borne cloud radar (CloudSat) data were analyzed. Statistical analysis suggests that stratospheric cirrus clouds occur on the order of 3.0 × 103times a year between 30 °S and 30 °N. Many of the stratospheric cirrus clouds are found in the pre-monsoon season in the South and Southeast Asia, where convection is deep and intense.