Nonequilibrium coexistence of solid and liquid particles in Arctic stratospheric clouds
Nonequilibrium coexistence of solid and liquid particles in Arctic stratospheric clouds
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北极平流层云中固体和液体粒子的非平衡共存
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
T. Peter
中科院分区：
文献类型：
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作者：
J. Biele;A. Tsias;B. Luo;K. Carslaw;R. Neuber;G. Beyerle;T. Peter
对斯匹次卑尔根州新奥勒松的极地平流层云（PSCs）的观测结果进行了检验，以量化固体颗粒的出现。极化后向散射比气溶胶去极化比在PSC中是非球形（固体）粒子存在的一个更敏感的指标，对于含有大量液滴的云，气溶胶去极化比接近于零。该分析证实了我们之前的发现，即Ia型psc不能由与气相平衡的三水合物硝酸颗粒组成，否则会导致过高的后向散射比。相反，以前被认为完全由液滴组成的Ib型psc通常含有非常少量的固体颗粒。这些云产生了高度平行的后向散射，这是由液滴散射引起的，并且由于很少的固体颗粒而产生了不消失的垂直信号。其他Ib型PSCs似乎只含有液体颗粒。混合液/固体云是在激光雷达仪器可分辨的最小时空尺度（30 m, 1 min）上观测到的，这意味着它们的性质不是不同云类型空间平均的结果。将观测结果与光学计算结果相比较表明，这种非平衡态粒子分布是可以预料到的，因为温度变化足够快，无法使粒子达到平衡态大小。Ia型和Ib型云观测到的光学特性可以在模型中重现，假设粒子中有很小一部分是由硝酸水合物组成的，大部分是二元H2SO4/H2O或三元HNO3/H2SO4/H2O液滴。
Observations of polar stratospheric clouds (PSCs) from Ny Alesund, Spitsbergen, have been examined to quantify the occurrence of solid particles. The polarized backscatter ratio was found to be a more sensitive indicator of the presence of non-spherical (solid) particles in a PSC than the aerosol depolarization, which approaches zero for clouds containing a large volume of liquid droplets. The analysis corroborates our previous finding that type Ia PSCs cannot be composed of nitric acid trihydrate particles in equilibrium with the gas phase, which would lead to a much too high backscatter ratio. Conversely, type Ib PSCs, previously thought to be composed solely of liquid droplets, often contain a very small fraction of solid particles. These clouds develop a high parallel backscatter, arising from Mie scattering by droplets, and a nonvanishing perpendicular signal due to the few solid particles. Other type Ib PSCs appear to contain only liquid particles. The mixed liquid/solid clouds are observed on the smallest spatial and temporal scale resolvable by the lidar instrument (30 m, l min), implying that their properties are not a result of spatial averaging of different cloud types. Comparison of the observations with optical calculations shows that such nonequilibrium particle distributions are to be expected, as temperature changes are sufficiently rapid to prevent the particles from assuming equilibrium sizes. The observed optical characteristics of type Ia and type Ib clouds can be reproduced in a model by assuming that a very small fraction of the particles are composed of nitric acid hydrate, with the majority being binary H2SO4/H2O or ternary HNO3/H2SO4/H2O droplets.