A new model of cloud drop distribution that simulates the observed drop clustering: effect of clustering on extinction coefficient estimates
| Knyazikhin, Yuri | Boston University |
| Marshak, Alexander | NASA Goddard Space Flight Center |
| Larsen, Michael | Michigan Technological University |
| Wiscombe, Warren | BNL/NASA Goddard Space Flight Center |
Category: Modeling
Cloud droplet size distribution is one of the most fundamental subjects in cloud physics. Understanding of spatial distribution and small-scale fluctuations of cloud droplets is essential for both cloud physics and atmospheric radiation. For cloud physics, it relates to the coalescence growth of raindrops while for radiation, it has a strong impact on a cloud’s radiative properties. We have developed new size dependent models of spatial distribution of cloud drops that simulate the observed clustering of drops. In contrast to currently used models that assume homogeneity and therefore a Poisson distribution of cloud drops, these models show strong drop clustering, the more so the larger the drops. Based on these models, the extinction coefficient was estimated in two ways. First, using a simple Monte Carlo procedure, we simulated the radiation field transmitted through a cloud volume without experiencing a collision. The extinction coefficient was then specified from this field. In the second case, the extinction coefficient was directly derived from first principles using spatial distribution of cloud drops. For this cloud volume, we analyzed the partitioning of the incident radiation into cloud transmission and interception numerically and analytically. The poster will discuss the impact of drop clustering on the extinction coefficient and the energy conservation law.
This poster will be displayed at the ARM Science Team Meeting.
