Collaborative Research: Dynamics of Unsaturated Downdrafts, Cold Pools, and Their Roles in Convective Initiation and Organization

潮湿对流在形成云/雨以及决定地球能量平衡和水资源分布方面发挥着关键作用。它们也在推动环流模式方面发挥着关键作用，因此对我们理解和预测天气和气候是至关重要的。由于这些过程发生在比全球天气和气候模式的网格尺寸更小的空间尺度上，它们需要与数值模式中的大尺度流动在统计上相关，或者用参数化来表示。参数化的成功需要对湿对流过程的物理和过程水平的了解。该项目侧重于潮湿对流的一个重要方面，即冷池。当雨水蒸发成不饱和空气时，它会冷却空气，增加空气的密度，使其下沉到地表，并以密度流的形式水平传播。这些密度流被称为冷池。它们可以引发新的风暴(这是人们在风暴之前经历的阵风和较冷空气的原因)，改变近地表通量，大气稳定性，并影响对流云的特征和发展。在这个项目中，使用高分辨率数值模拟，明确地解析冷池和产生冷池的过程，并结合创新的粒子跟踪来揭开导致冷池产生、演变和消亡的许多因素，以及量化冷池如何改变潮湿对流的特征，以及如何在全球天气和气候模式中统计地表示这些影响。云和对流仍然是天气和气候预测中的主要不确定性来源。通过改进对流云的一个关键特征的过程级别的理解和表示，这项研究将有助于减少这种不确定性。这项研究还将加强大学科学家和博士后科学家之间的合作，并为天气和气候模型的开发做出贡献。

Moist convections play a critical role in giving rise to clouds/rains and in determining the energy balance of the earth and the distribution of water resources. They also play a key role in forcing the circulation patterns, and thus are central to our understanding and prediction of weather and climate. Because these processes occur at spatial scales smaller than that of the grid sizes of global weather and climate models, they need to be related to large-scale flow statistically in numerical models, or represented by parameterizations. The success of parameterizations demands physically based and process-level understanding of the moist convective processes. This project focuses on one important aspect of moist convections, namely cold pools. When rain evaporates into unsaturated air, it cools the air and increases its density, causing it to sink to the surface and spread out horizontally as a density current. These density currents are known as cold pools. They can trigger new storms (which is responsible for the gusty winds and cooler air that one experiences preceding a storm), modify near-surface fluxes, atmospheric stability, and affect the characteristics and development of convective clouds. In this project, high-resolution numerical simulations that explicitly resolve the cold pools and processes that produce them are used along with innovative particle tracking to unravel the many factors that contribute to the birth, evolution, and demise of cold pools, as well as to quantify how cold pools modify the characteristics of moist convections and how to represent these effects statistically in global models of weather and climate.Clouds and convection remain major sources of uncertainty in weather and climate predictions. By improving process-level understanding and representation of a key feature of convective clouds, this research will help reduce such uncertainties. This research will also strengthen collaboration between university scientists and train postdoctoral scientists, and contribute to the development of weather and climate models.