Development and Testing of a Global Quasi-3-D Multi-scale Modeling Framework

用于天气预测和气候模拟的全球大气环流模式(GCM)通常将大气划分为一个网格，每个网格框中只有一个大气变量的值，如温度和压力。由于网格框通常有几十公里宽或更多，因此不可能在这样的模型中表示单独的云，甚至是云系统。相反，云和其他小规模过程对较大尺度大气流动的净影响必须通过使用参数来近似，而这种表示是天气预报误差和未来气候变化预测不确定性的关键来源。因此，代表云层及其与大尺度大气条件相互作用的替代方法对于预报天气和为关注气候变化和变化的影响的利益相关者提供决策支持是可取的。该奖项支持一种新的大气模式的开发和测试，即全球准3D多尺度模拟框架(Q3D MMF)。该模式是由科学和技术中心大气过程多尺度模式中心(见AGS-0425247)开发的超参数方案的扩展。SP MMF由一个全球大气环流模式(GCM)组成，其中每个网格列的云过程和其他亚网格尺度过程的参数化被一个高分辨率云分辨率模式(CRM)所取代。CMMAP已经制作了社区大气模式的SP版本(CAM，或SP版本的SP-CAM)。但SP-CAM使用二维(2D)CRM，其中区域是在纬向(x-)或子午线(y-)方向上定向的垂直平面，以及在x-或y-方向上的周期性边界条件。这些限制是为了降低计算成本而施加的，完全放宽这些限制将需要一个全球CRM(GCRM)，对于大多数目的来说，这在计算上过于昂贵。或者，Q3D MMF通过使用具有域的CRM来部分地放宽条件，所述域是在跨通道域中仅具有几个网格点的窄通道。这些通道与GCM相邻小区中的对应通道相连，从而避免了通道两端的周期性边界条件。此外，GCM的每个网格单元都有两个这样的通道形状的CRM，它们在纬向和子午线方向上定向，以允许由于表面地形和其他因素而产生的方向各向异性。因此，纬向和经向CRM通道在全球范围内不间断地延伸，并在父GCM的相邻网格单元处彼此相交。通道模型在交叉点处不交互，因为这将导致与十字形区域相关联的非物理行为。单独的CRM频道只与GCM通信，从GCM接收背景信息，并向GCM提供从常规GCM中发现的标准网格柱参数化所预期的输出。这里的工作是CMMAP以前工作的扩展，包括开发一个更简单的版本，其中CRM嵌入到理想热带区域的区域模式中。该奖项下的工作包括从这个原型开发全球模式所需的几项任务，包括包括地形和从周期性笛卡尔区域到现实GCM区域的转换。这项工作对研究界产生了更广泛的影响，因为它开发了一种新的大气模型，适用于与云对大范围天气和气候现象的影响有关的一系列研究领域。为了确保更广泛的研究社区的可访问性，Q3D MMF将使用作为GCM组件的CAM版本(光谱元素版本)来构建。CAM是免费提供的，得到了良好的支持和记录，并得到了广泛的使用，从而最大限度地提高了可访问性。此外，CAM是共同体地球系统模型的大气组成部分模型，用于预测未来的气候变化，为关注气候对自然和人类系统的影响的决策者提供信息。

Global atmospheric general circulation models (GCMs) used for weather prediction and climate modeling typically divide the atmosphere into a grid, with a single value for atmospheric variables like temperature and pressure in each grid box. As the grid boxes are typically tens of kilometers wide or more it is not possible to represent individual clouds, or even cloud systems, in such models. Instead the net effect of clouds and other small-scale processes on the larger scale atmospheric flow must be approximated through the use of parameterizations, and this representation is a key source of errors in weather forecasts and uncertainty in future climate change projections. Alternative methods of representing clouds and their interactions with large-scale atmospheric conditions are therefore desirable for forecasting the weather and providing decision support to stakeholders concerned with the impacts of climate variability and change.This award supports the development and testing of a novel atmospheric model, the global quasi-3D Multiscale Modeling Framework (Q3D MMF). The model is an extension of the Super-Parameterizaton (SP) scheme developed by the Center for Multiscale Modeling of Atmospheric Processes (CMMAP, see AGS-0425247), the Science and Technology Center (STC). The SP MMF consists of a global atmospheric general circulation model (GCM) in which the parameterizations for cloud processes and other subgrid-scale processes in each grid column are replaced by a high-resolution cloud resolving model (CRM). CMMAP has already produced an SP version of the Community Atmosphere Model (CAM, or SP-CAM for the SP version). But SP-CAM uses a two-dimensional (2D) CRM in which the domain is a vertical plane oriented in either the zonal (x-) or meridional (y-) direction and periodic boundary conditions in the x- or y-direction. These restrictions are imposed to reduce computational cost, and to relax them entirely would require a global CRM (GCRM) which is too computationally expensive for most purposes. Alternatively, the Q3D MMF partially relaxes the conditions by using CRMs with domains that are narrow channels with only a few gridpoints in the cross-channel domain. The channels connect with their counterparts in neighboring cells of the GCM, thus avoiding periodic boundary conditions at either end of the channel. Moreover, each grid cell of the GCM has two such channel-shaped CRMs, oriented in the zonal and meridional direction, to allow for directional anisotropy due to surface topography and other factors.The zonal and meridional CRM channels thus extend around the globe without interruption and intersect each other at adjacent grid cells of the parent GCM. The channel models do not interact at the intersections, as that would result in unphysical behavior associated with a cross-shaped domain. The separate CRM channels communicate only with the GCM, receiving background information from the GCM and supplying the GCM with the outputs expected from standard grid column parameterizations found in conventional GCMs. Work here is an extension of previous work at CMMAP, including the development of a simpler version in which the CRMs are embedded in a regional model over an idealized tropical domain. Work under this award includes several tasks required to develop a global model from this prototype, including inclusion of topography and conversion from a periodic Cartesian domain to a realistic GCM domain.The work has broader impacts for the research community because it develops a new atmospheric model which is applicable to a range of research areas related to the impact of clouds on large-scale weather and climate phenomena. To ensure accessibility to the broader research community, the Q3D MMF will be constructed using a version of CAM (the spectral element version) as the GCM component. CAM is freely available, well supported and documented, and widely used, thereby maximizing accessibility. In addition, CAM is the atmospheric component model of the Community Earth System Model, which is used for projections of future climate change that inform decision makers concerned with climate impacts on natural and human systems.