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范雯露, 景晓琴, 杨璟, 等. 2022. 基于飞机观测的美国落基山地区冬季混合相态层状云与夏季对流云的微物理特征[J]. 大气科学, 46(5): 1113−1131. doi: 10.3878/j.issn.1006-9895.2107.21046
引用本文: 范雯露, 景晓琴, 杨璟, 等. 2022. 基于飞机观测的美国落基山地区冬季混合相态层状云与夏季对流云的微物理特征[J]. 大气科学, 46(5): 1113−1131. doi: 10.3878/j.issn.1006-9895.2107.21046
FAN Wenlu, JING Xiaoqin, YANG Jing, et al. 2022. Microphysical Characteristics of Winter Mixed-Phase Stratiform Clouds and Summer Convective Clouds in the Rocky Mountain Region Based on Airborne Measurements [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 46(5): 1113−1131. doi: 10.3878/j.issn.1006-9895.2107.21046
Citation: FAN Wenlu, JING Xiaoqin, YANG Jing, et al. 2022. Microphysical Characteristics of Winter Mixed-Phase Stratiform Clouds and Summer Convective Clouds in the Rocky Mountain Region Based on Airborne Measurements [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 46(5): 1113−1131. doi: 10.3878/j.issn.1006-9895.2107.21046

基于飞机观测的美国落基山地区冬季混合相态层状云与夏季对流云的微物理特征

Microphysical Characteristics of Winter Mixed-Phase Stratiform Clouds and Summer Convective Clouds in the Rocky Mountain Region Based on Airborne Measurements

  • 摘要: 混合相态层状云与对流云的微物理特征有很大的差异性,但现阶段数值模式中并没有充分考虑两者的区别,这是导致云降水的模拟有较大不确定性的原因之一。为了加深对层状云与对流云的微物理特征差异的理解,并为模式的验证和参数化开发提供支撑,本文基于在中落基山地区进行的Ice in Clouds Experiment—Layer Clouds(ICE-L)项目和High Plain Cumulus(HiCu)项目的飞机观测资料,定量对比分析了该地区大陆性混合相态冬季较浅薄的层状云与较弱及中等强度的夏季对流云的微物理特征。其中,粒子图像和粒子谱通过2D-Cloud和2D-Precipitation探头得到,液态水含量通过热线式King探头测量得到,冰水含量基于粒子谱计算得到。主要结论有:(1)在−30°C~0°C的温度层范围内,夏季对流云内的液态水含量比冬季层状云高一个数量级,冰水含量高一到两个数量级,并且在对流云云顶附近观测到更多的过冷水。此外,夏季对流云中液态水含量在−20°C~0°C上随温度降低而升高,而冬季层状云则相反。夏季对流云中更活跃的冰晶生成和生长过程使得云内液态水质量分数小于层状云。(2)冬季层状云与夏季对流云内相态空间分布极不均匀。随着温度从0°C降低到−30°C,在冬季层状云中冰晶发生贝吉龙过程,云中的过冷水为主的区域向混合相态和冰相转化。而夏季对流云中相态结构更为复杂,体现了对流云中复杂的冰水相互作用。(3)在−30°C~0°C的温度范围内,夏季对流云的粒子谱宽度大于冬季层状云。随着温度的降低,冬季层状云与夏季对流云均存在粒子谱增宽的现象。(4)冬季层状云中,温度低于−20°C时冰晶主要为无规则状,在−20°C~−10°C观测到了辐枝状和无规则状冰晶,在−10°C以上观测到了柱状和无规则状冰晶,说明冰晶的生长主要为凝华增长和碰并增长。而夏季对流云以冻滴、霰粒子与不规则冰晶为主,说明主要为液滴冻结、淞附增长和碰并增长为主。(5)在夏季对流云较强的上升气流中存在较高的液态水含量,但垂直速度与云内冰水含量没有明显的相关性。

     

    Abstract: The microphysical characteristics of mixed-phase stratiform and convective clouds are different but have not been well considered in numerical models, leading to uncertainties in modeling clouds and precipitation. To improve our understanding of the difference in microphysics between mixed-phase stratiform and convective clouds and obtain quantitative results for model evaluation and parameterization, the microphysical characteristics of continental winter mixed-phase stratiform and summer convective clouds in the mid-Rocky Mountain region are compared using data collected during the Ice in Clouds Experiment—Layer Clouds (ICE-L) and the High Plain Cumulus (HiCu) projects. The particle images and Particle Size Distributions (PSD) were measured using 2D cloud and 2D precipitation probes, Liquid Water Content (LWC) was measured using the King hot-wire probes, and Ice Water Content (IWC) was calculated based on the particle spectrum. The main findings are as follows: (1) Between −30°C and 0°C, the LWC in summer convective clouds is an order of magnitude higher than that in winter stratiform clouds, and the IWC in summer convective clouds is 1–2 orders of magnitude higher than that in winter stratiform clouds. Supercooled liquid water was observed near the convective cloud top. The LWC in summer convective clouds increases with the decrease in temperature from 0°C to −20°C, while the LWC in winter stratiform clouds decreases with the decrease in temperature. The liquid fraction in summer convective clouds is smaller than that in winter stratiform clouds, indicating rapid ice production. (2) Both winter stratiform and summer convective clouds had large spatial variability in their phase distribution. As the temperature decreased from 0°C to −30°C, ice in winter stratiform clouds grew through the Bergeron process, and the water-dominated zones transformed into the mixed-phase and ice-dominated zones. The phase distribution was complicated in summer convective clouds, indicating a complex liquid–ice interaction. (3) The ice PSD in summer convective clouds was broader than that in winter stratiform clouds between 0°C and −30°C. As the temperature decreased, the ice PSDs in both winter stratiform and summer convective clouds broadened. (4) The observed particle images in winter stratiform clouds were irregular at temperatures lower than −20°C. Meanwhile, between −20°C and −10°C, the ice was dendritic and irregular, and at temperatures warmer than −10°C, the ice was mainly needle-shaped, columnar, and irregular, indicating that the ice grew through vapor diffusion and coalescence in winter stratiform clouds. In summer convective clouds, the ice mainly formed through drop freezing, riming, and coalescence. (5) In strong updrafts of summer convective clouds, a high LWC and large liquid fractions were observed. The IWC had no obvious correlation with vertical velocity, indicating that the efficiency of glaciation in HiCu clouds was independent of vertical velocity.

     

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