Collaborative Research: Convective Organization and Climate

本研究小组将制定并应用一个简化的数值模型来探索有利于潮湿大气对流自聚集的条件。积云对流聚集成包含许多单个对流细胞的团块，在自然界和全物理数值大气模拟中都很突出。研究人员使用大气模拟系统（SAM）数值模式进行了初步分析，并将在这些模拟的基础上进行扩展，以解决对流的自聚集将导致地表温度系统性下降的假设，而这种下降可能反过来导致对流的分解和地表的恢复再变暖。这样，系统自然会被聚集态和分解态之间的相变所吸引，并将构成自组织临界系统的一个例子。提出的工作目标是：(1)了解自聚集的物理学，(2)确定系统中存在多少滞后，(3)确定具有表面能量平衡的辐射对流平衡系统是否受到自组织临界的影响，以及(4)了解上述因素对基于理想化辐射对流状态以及更多现实世界条件的气候的影响。这项工作的智力价值源于对影响潮湿大气对流机制的基本理解的提高，潮湿大气对流是气候系统的一个关键组成部分，但仍未得到充分理解。对热带气候趋向于自组织临界状态这一假设的证实可以大大促进对对流和气候之间相互关系的理解。这项研究的更广泛的影响包括在两个合作机构中的每一个的研究生教育和培训。这项工作也有可能通过改进的参数化来改进对流的表示，这些参数化适合纳入耦合气候模式，从而有助于改进气候预报。

This research team will formulate and apply a simplified numerical model to explore conditions favoring the self-aggregation of moist atmospheric convection. Aggregation of cumulus convection into clumps containing many individual convective cells is prominent in nature and in full-physics numerical atmospheric simulations alike. The researchers have performed preliminary analyses using the System for Atmospheric Modeling (SAM) numerical model, and will expand upon these simulations in order to address the hypothesis that self-aggregation of convection will lead to a systematic decline in the surface temperature, and that such decline may in-turn lead to disaggregation of convection and restorative re-warming of the surface. As such, the system would naturally be attracted to the phase transition between aggregated and disaggregated states and would constitute an example of a self-organized critical system. The objectives of the proposed work are to: (1) understand the physics of self-aggregation, (2) determine how much hysteresis there is in the system, (3) determine whether radiative-convective equilibrium systems with surface energy balance are subject to self-organized criticality, and (4) understand the implications of these aforementioned factors upon climates predicated on idealized radiative-convective states as well as more real-world conditions.The intellectual merit of the work derives from improved basic understanding of mechanisms influencing moist atmospheric convection, which is a critical but nonetheless not fully understood component of the climate system. A confirmation of the hypothesis that tropical climate tends toward a state of self-organized criticality could substantially advance the understanding of the interrelationship between convection and climate.The broader impacts of the study include the education and training of a graduate student at each of two collaborative institutions. The work also has potential to lead to improved representations of convection via improved parameterizations suitable for incorporation into coupled climate models, which could in turn contribute to improved climate forecasts.