Wind tunnel investigations on riming of ice particles: Retention of water-soluble organics and the influence of turbulence on the growth of graupels.

近年来，大气中的气体和颗粒有机物种受到越来越多的关注。在云和雨水以及雪样本中都发现了有机化合物。然而，它们的清除过程并没有被充分地理解，因此这些是可以在数值模型中整合的。通过冰相的一种可能性是有机物在冰冻期间的滞留，即在冰粒上沉积过冷的水滴。在这个过程中，有机物质（或其数量的一部分）可以转移到冰相并被保留，而另一部分被释放回气相。这些部分将在风洞实验中进行研究和量化，在风洞实验中，自由漂浮的冰粒和雪花暴露在含有对大气有重要意义的有机物质的过冷液滴云中。由于云水中最丰富的水溶性有机物是羧酸类和醛类，因此提出的实验主要扩展到这些基团。另一个非常有趣的话题是湍流对微物理过程的影响。湍流显著增强了云滴的碰撞生长；因此，在冰相的类似过程中，预计会有类似的结果。在紊流条件下，通过边缘来确定冰粒的生长速度，这是为云物理和化学的建模而制定更现实的收集核（与层流情况相比）所必需的。

In recent years, gaseous and particulate organic species in the atmosphere have received increased attention. Organic compounds are found in cloud and rain water as well as in snow samples. However, the removal processes underlying their scavenging is not adequately enough understood such that these are amenable for integration in numerical models. One possibility via the ice phase would be the retention of organics during riming, i.e. the deposi-tion of super-cooled water droplets on ice particles. During this process, the organic species (or fractions of their amounts) can be transferred into and retained by the ice phase while another fraction is released back into the gas phase. These fractions will be investigated and quantified in wind tunnel experiments where freely floating ice particles and snow flakes are exposed to clouds of supercooled droplets containing organic substances of atmospheric significance. As the most abundant water-soluble organics in cloud water are carboxylic ac-ids and aldehydes the proposed experiments mainly extend over these groups. Another topic of great interest is the influence of turbulence on microphysical processes. The collisional growth of cloud droplets is significantly enhanced by turbulence; therefore, similar results are expected in the case of riming as an analogous process in the ice phase. The determination of the growth rate of ice particles by riming under turbulent conditions is necessary for the – so far not yet available - formulation of more realistic collection kernels (in comparison to the laminar case) for the modeling of cloud physics and chemistry.