Global Atmospheric Modeling Hierarchy Development

该项目旨在通过开发和使用不同复杂程度的理想化模型来促进对理论气候动力学的理解。这些模式的复杂程度只与捕捉感兴趣的现象所需要的程度相同，这些现象被认为是基本气候系统过程的表现。其中一种模型是赫尔德-苏亚雷斯模型（HS，以其创造者的名字命名），它不包括云或潮湿过程，而是利用热松弛来产生赤道和两极之间的温度对比。尽管该模型简单，但它再现了大气环流的许多特征，包括急流、对中纬度天气系统的合理近似，以及被称为哈德利环流的热带翻转环流。HS模型的一个用途是检验一个假设，即大气环流的关键方面，包括动能产生的活力和从较暖纬度向较冷纬度输送的热量，可以用最大熵产（MEP）来理解。MEP可以用来推导HS模型中动能生成的上限，但上限太大，除非施加约束，使其依赖于行星自转速率和其他基本参数，否则无法使用。这里进行的研究试图确定HS模式中的适当限制，并评估它们与更复杂的模式和观测到的大气的相关性。其他需要解决的问题包括对流层低层波动量通量在风暴路径动力学中的作用，将西风动量从中纬度输送到热带的波不稳定性，以及外部罗斯比波的产生机制。HS模型通过纳入水文循环的简化表示来解决其他问题，其中水蒸气被视为无辐射效应的被动示踪剂。表面蒸发根据标准体积公式进行，水蒸气在更高和更冷的高度饱和时凝结。但凝结不会产生云或潜热，水循环对大气环流没有影响。尽管有这些遗漏，但该模型产生的水汽流带、锋面降水模式和大气河流与现实世界的对应物相似。该模型用于研究水文循环平均强度的运动学约束及其对大陆变暖条件的响应。对于后一种应用，使用土壤湿度的简化“桶”表示来指定大陆。进一步的研究是用一个复杂程度稍高的模型进行的，该模型使用简化的大气辐射传输（灰体近似）而不是热松弛来产生两极到赤道的温度对比。该模式允许水循环通过冷凝加热影响环流，但水蒸气对辐射传输没有影响，也没有云。这个版本的模式用于研究热带辐合带（ITCZ）的行为，热带辐合带是通常在赤道附近发现的云和降水的窄带。一种策略是修改模式，使其只代表大气的一个有限的纬向扇区，从而消除比扇区宽度更大的现象对ITCZ造成的干扰。通过一个门户网站与研究界共享模型代码和文档，这项工作具有更广泛的科学影响。这些模型的不同版本已经作为研究工具得到了广泛的接受，但它们主要是通过与pi的研究小组的个人联系传播的。除了在分离和检验特定气候系统过程方面的价值外，这些模式已被证明可用于检验综合气候模式中使用的数值方法。此外，这些模式在向公众和其他科学领域的研究人员传播气候科学方面可以发挥重要作用。简单的模式对这一目的是有价值的，因为它们可以用来证明有效交流所需的简化正确地代表了气候系统的运作，尽管是以近似的形式。该项目还为研究生提供支持和培训，从而为该研究领域的劳动力发展提供支持。

This project seeks to advance understanding in theoretical climate dynamics through the development and use of idealized models of varying levels of complexity. The models are designed to be only as complex as necessary to capture the phenomena of interest, which are assumed to be manifestations of fundamental climate system processes. One such model is the Held-Suarez model (HS, named for its creators), which does not include clouds or moist processes and uses thermal relaxation to generate the temperature contrast between the equator and the poles. Despite its simplicity the model reproduces many features of the atmospheric circulation including jet streams, reasonable approximations of middle-latitude weather systems, and the tropical overturning circulations known as Hadley cells.One use of the HS model is to test the hypothesis that key aspects of the atmospheric circulation, including the vigor of kinetic energy generation and the amount of heat transported from warmer to colder latitudes, can be understood in terms of Maximum Entropy Production (MEP). MEP can be used to derive an upper bound on kinetic energy generation in the HS model, but the upper bound is too large to be useful unless constraints are imposed which make it dependent on planetary rotation rate and other fundamental parameters. Research conducted here attempts to identify the appropriate constraints in the HS model and assess their relevance for more sophisticated models and the observed atmosphere. Other problems to be addressed include the role of lower tropospheric wave momentum fluxes in stormtrack dynamics, wave instabilities that transport westerly momentum from the middle latitudes into the tropics, and generation mechanisms for external Rossby waves.Additional problems are addressed with the HS model by incorporating a simplified representation of the hydrological cycle in which water vapor is treated as a passive tracer without radiative effects. Surface evaporation proceeds according to a standard bulk formula and water vapor condenses when it saturates at higher and colder altitudes. But the condensation does not result in clouds or latent heating and water cycling has no effect on atmospheric circulation. Despite these omissions the model produces water vapor streamers, frontal precipitation patterns, and atmospheric rivers which resemble their real-world counterparts. The model is used here to study kinematic constraints on the mean strength of the hydrological cycle and its response over continents to warmer conditions. For the latter application continents are specified using a simplified "bucket" representation of soil moisture.Further research is conducted with a model at a somewhat higher level of complexity, which uses simplified atmospheric radiative transfer (the grey-body approximation) rather than thermal relaxation to produce the pole-to-equator temperature contrast. The model allows the hydrological cycle to affect circulation through condensational heating, but water vapor has no effect on radiative transfer and clouds are not represented. This version of the model is used to study the behavior of the intertropical convergence zone (ITCZ), the narrow band of clouds and precipitation usually found near the equator. One strategy is to modify the model so that it represents only a limited zonal sector of the atmosphere, so that disturbances of the ITCZ caused by phenomena larger than the width of the sector are eliminated.The work has scientific broader impacts through the sharing of model codes and documentation with the research community through a web portal. Versions of the models have already gained broad acceptance as research tools, but they have been disseminated largely through personal connections with the PIs' research group. Beyond their value for isolating and examining specific climate system processes, the models have proven useful for testing numerical methods used in comprehensive climate models. In addition, the models can play an important role in communicating climate science to the public and researchers in other scientific fields. Simple models are valuable for this purpose as they can be used to demonstrate that the simplifications required for effective communication correctly represent, albeit in approximate form, the workings of the climate system. The project also provides support and training for a graduate student, thereby providing for workforce development in this research area.