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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >FIELD OBSERVATIONS IN CONTINENTAL STRATIFORM CLOUDS - PARTITIONING OF CLOUD PARTICLES BETWEEN DROPLETS AND UNACTIVATED INTERSTITIAL AEROSOLS
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FIELD OBSERVATIONS IN CONTINENTAL STRATIFORM CLOUDS - PARTITIONING OF CLOUD PARTICLES BETWEEN DROPLETS AND UNACTIVATED INTERSTITIAL AEROSOLS

机译：连续层状云的实地观测-液滴与未活化的气溶胶间的云团划分

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The partitioning of cloud particles between activated droplets and unactivated interstitial aerosols is a primary determinant of cloud microphysical, radiative, and chemical properties. In the present study, high-resolution aircraft measurements (1 s, similar to 60 m) of the number concentrations (N-amp and N-cd) of accumulation-mode particles (AMP, 0.17 to 2.07 mu m diameter) and cloud droplets (CD, 2 to 35 mu m diameter), made during 10 flights in and around continental stratiform clouds near Syracuse, New York, in autumn 1984 have been used to study the local and instantaneous nature of cloud particle partitioning throughout the sampled clouds. The partitioning is defined as the activated fraction F (= N-cd/N-tot) of all measured cloud particles (N-tot = N-amp + N-cd). F may be interpreted approximately as the AMP activation efficiency which is often assumed to be unity in all clouds. In the present study, F varied over its full possible range (0 to 1), being low especially in cloud edges. Even in the near-adiabatic parts of cloud interior, its variation ranged from 0.1 to 1 over the 10 days. Statistically, its value in cloud interior exceeded 0.9 in 36% of the data but was below 0.6 in 28%. On 5 of the 10 days, stratocumulus clouds were embedded in cool, dry, and relatively clean (N-tot < 600 cm(-3)) northerly air masses. In such cases, cloud droplet concentration increased approximately linearly with increasing total particle loading, and F in cloud interior was near unity and relatively insensitive to changes in the influencing variables. On the other clays, especially in stratus clouds embedded in warm and polluted southerly air masses, F was significantly less than unity, with particles in the smallest size ranges (0.17 to 0.37 mu m) activating only fractionally depending on several factors. An important feature of the clouds sampled in this study was the existence of multiple cloud layers and complex vertical thermal structure on most days. Consequently, our analysis of the dependence of F on influencing cloud variables has been based on data grouped into individual cloud layers. Besides the size of the precursor aerosol, we found total particle loading (N-tot) and the local vertical cooling rate (similar to temperature lapse rate in individual layers) to influence F the most. In particular, F decreased with increasing particle loading in excess of about 800 cm(-3), and increased nearly linearly with temperature lapse rate. Evidently, the activation process can become self-limiting in stratiform clouds under polluted conditions, in which case increasing anthropogenic aerosol loading of the atmosphere translates less and less into cloud droplet population. This observation has important implications with respect to cloud radiative forcing, precipitation formation and acidification, and for long range transport of the unactivated aerosols. [References: 55]
机译：云颗粒在活化液滴和非活化间隙气溶胶之间的分配是决定云微物理，辐射和化学性质的主要因素。在本研究中，高分辨率飞机测量（1 s，类似于60 m）累积模式粒子（AMP，直径为0.17至2.07μm）和云滴的数量浓度（N-amp和N-cd） CD（直径2至35微米）是在1984年秋天在纽约锡拉丘兹附近的大陆层状云中及其周围进行的10次飞行过程中制作的，用于研究整个采样云中云粒子分配的局部和瞬时性质。划分被定义为所有测得的云粒子的活化分数F（= N-cd / N-tot）（N-tot = N-amp + N-cd）。 F可以近似地解释为AMP激活效率，在所有云中通常假定其为1。在本研究中，F在其整个可能范围内（0到1）变化，尤其在云边缘时较低。即使在云层内部绝热的部分中，其变化在10天中也从0.1到1不等。从统计上讲，其在云内部的值在36％的数据中超过0.9，但在28％的数据中低于0.6。在10天中的5天中，平层积云埋在凉爽，干燥且相对干净的北气团中（N-tot <600 cm（-3））。在这种情况下，云滴浓度随总颗粒负荷的增加而呈线性增加，而云内部的F接近于1，并且对影响变量的变化相对不敏感。在其他粘土上，尤其是埋藏在温暖和污染的南方空气中的地层云中，F显着小于1，最小尺寸范围（0.17至0.37μm）的颗粒仅取决于几个因素而被部分活化。在这项研究中采样的云的一个重要特征是在大多数日子中存在多个云层和复杂的垂直热结构。因此，我们对F对影响云变量的依赖性的分析基于分组到各个云层的数据。除了前驱气雾剂的大小，我们发现总颗粒装载量（N-tot）和局部垂直冷却速率（类似于各个层中的温度下降速率）对F的影响最大。尤其是，F随着超过约800 cm（-3）的颗粒载荷的增加而降低，并随温度的降低速率线性增加。显然，在受到污染的条件下，层状云中的活化过程会变得自限，在这种情况下，不断增加的人为气溶胶含量会越来越少地转化成云滴。该观察结果对云辐射强迫，降水形成和酸化以及未活化气溶胶的远距离迁移具有重要意义。 [参考：55]

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