CAREER: Understanding the Role of Oceans in the Planetry Energy Budget

这是一个CAREER提案，其研究目标是了解海洋热传输（OHT）和海洋热吸收（OHU）在行星能量收支中的作用。这里OHU指的是热量从海洋表面向深处的转移，在那里热量不再影响上覆大气，从而有效地从表层气候中去除热量，持续数年至数十年或更长时间。OHT指的是热量从一个地区的表面被带走，由地下海洋输送，并在另一个地区重新出现的热传输。OHU在气候变化中的作用已经成为一些人感兴趣的话题，因为OHU的增加可以解释20世纪末之后全球变暖的中断。该项目的进一步动机来自于建模研究，该研究表明，即使在总热吸收相同的情况下，不同的OHU空间模式可以引起不同的全球变暖抑制量。在某种程度上，这些差异可以用区域气候反馈来解释。例如，海冰反照率反馈可以在放大温室气体（GHG）增加引起的全球变暖方面发挥重要作用，但海冰只发生在靠近两极的寒冷地区。通过OHU或OHT去除高纬度地区的地表热量可以减少这些地区温室气体引起的变暖，从而减少海冰反照率反馈的放大效应。但是PI和其他人之前的工作表明，OHU和OHT的影响不能完全用区域气候反馈来解释，区域气候反馈或多或少取决于海洋如何转移热量。此外，如果不考虑大气能量输运的作用，就不能理解OHU和OHT的影响。先前的一项研究发现，如果OHU将热量从热带海洋中带走（或者OHT将热量从热带地区转移出去），那么大气中湿静态能的传输将非常有效地将影响扩散到热带地区以外，并均匀地冷却全球。但是，在高纬度地区，等量的热量去除反而会产生集中的高纬度冷却，这种差异可以用温暖的热带地区和寒冷的两极之间强烈的背景水分对比来解释。这项工作主要关注海洋在当前和未来气候变化中的作用，但它也将考虑OHT在产生低纬度和高纬度之间温度对比减弱的过去气候中的作用，例如显生宙和始新世早期发生的气候。研究还将考虑水文循环对OHU和OHT的响应，重点是亚热带地区。过去的研究表明，虽然全球变暖模拟经常发现亚热带干燥，但OHT引起的亚热带变暖可能产生相反的效果。因此，在热带海洋吸收的热量被输送到亚热带的程度上，OHT可以抵消温室气体引起的干燥，这是一个潜在的相关效应，因为最近的研究结果将赤道太平洋的变暖中断与OHU联系起来。该项目的研究议程有两个关键组成部分。首先，大部分工作将使用简化的气候模型进行，其中海洋成分模型将被“平板海洋”取代，后者可以吸收热量并与大气发生热相互作用，但不能输送热量。在这种情况下，热量OHT和OHU以热源和汇的形式从外部施加到OHT汇聚和发散的区域，以及热量被隔离在深海中的区域。这种外强迫是常用的，一般称为q通量强迫。这些实验允许孤立地检查反馈和大气传输，而没有相互作用的海洋带来的复杂性。其次，这些实验的结果往往依赖于模型，因此需要一个模型集合来确定对施加的OHT和OHU强迫的响应的哪些方面是稳健的。为了解决这个问题，PI将组织一个模型相互比较项目（MIP），在这个项目中，将使用几个不同的模型进行一组共同的实验。一些实验将由PI进行，但他也将征求其他研究人员对MIP的贡献。进一步的研究将包括对耦合模式比对项目第5版（CMIP5）中最先进的气候模式的全球变暖模拟进行检查，以及用单一板块海洋气候模式进行扰动物理敏感性实验。这个CAREER项目的教育部分集中在用Python语言开发一个灵活的气候建模和分析包。这项教育活动旨在解决大气科学系本科生和研究生普遍缺乏计算机技能的问题。具体的任务是：1)用Python语言开发一门实用科学计算的简短入门课程；2)开发基于python的模块化气候建模和分析工具包；3)开发一系列互动教育模块，说明气候和大气科学的基本原理。有几个因素促使选择Python作为首选语言，包括其固有的模块化，它作为编译Fortran和C代码的“包装器”的能力，从而促进了已建立代码的无缝使用，以及该语言可用的众多可视化和软件开发工具。要开发的软件将是开源的，免费在线提供，并有良好的文档。它将由若干简化的动力核心和过程模型（辐射传输、边界层湍流通量等）组成，这些模型可以单独集成，也可以以各种方式组合成一个简单的气候模型。除了校内教学活动，基于python的模块将被开发用于当地高中生的夏令营。

This is a CAREER proposal in which the research goal is to understand the roles of ocean heat transport (OHT) and ocean heat uptake (OHU) in the planetary energy budget. Here OHU refers to the transfer of heat from the ocean surface to depths at which the heat no longer longer affects the overlying atmosphere, thus effectively removing heat from the surface climate for a period of years to decades or longer. OHT refers to heat transport in which heat is removed from the surface in one region, transported by the subsurface ocean, and resurfaces in another. The role of OHU in climate change has become a topic of some interest, as increased OHU could explain the hiatus in global warming following the end of the 20th century. Further motivation for the project comes from modeling studies showing that different spatial patterns of OHU can cause different amounts of global warming suppression, even when the total heat uptake is the same. To some extent these differences can be explained in terms of regional climate feedbacks. For example the sea ice albedo feedback can play a significant role in amplifying the global warming caused by greenhouse gas (GHG) increases, but sea ice only occurs in cold regions near the poles. Removal of surface heat from high latitudes by OHU or OHT could reduce GHG-induced warming in these regions and thus reduce the amplifying effect of the sea ice albedo feedback. But previous work by the PI and others suggests that the effects of OHU and OHT cannot be entirely explained in terms of regional climate feedbacks activated to a greater or lesser extent depending on how the oceans redirect heat. In addition, the effects of OHU and OHT cannot be understood without considering the role of atmospheric energy transport. A previous study found that if OHU removes heat from the tropical oceans (or if OHT transfers heat out of the tropics), atmospheric transport of moist static energy will be quite efficient in spreading the effect beyond the tropics and evenly cooling the globe. But an equivalent heat removal in high latitudes instead produces concentrated high latitude cooling, a difference which can be explained in terms of the strong background moisture contrast between the warm tropics and the cold poles. The work is primarily concerned with the ocean's role in current and future climate change, but it will also consider the role of OHT in producing past climates in which the temperature contrast between low and high latitudes was reduced, such as occurred in the Phanerozoic and early Eocene. The research will also consider the response of the hydrological cycle to OHU and OHT, with a focus on the subtropics. Past work suggests that while global warming simulations often find subtropical drying, subtropical warming due to OHT can produce the opposite effect. Thus OHT could counteract GHG-induced drying to the extent that heat absorbed by the tropical oceans is transported to the subtropics, a potentially relevant effect given recent results relating the warming hiatus to OHU in the equatorial Pacific.The research agenda for the project has two key components. First, much of the work will be conducted using simplified climate models in which the ocean component model is replaced by a "slab ocean", which can absorb heat and interact thermally with the atmosphere, but which cannot transport heat. In this context heat OHT and OHU are externally imposed in the form of heat sources and sinks applied to regions where OHT converges and diverges, and where heat is sequestered in the deep ocean. Such external forcing is commonly used and is generally referred to as Q-flux forcing. The experiments allow the feedbacks and atmospheric transports to be examined in isolation, without the complications introduced by an interactive ocean. Second, the results of such experiments are often model dependent, and thus an ensemble of models is required to determine which aspects of the response to imposed OHT and OHU forcing are robust. To address this issue, the PI will organize a model intercomparison project (MIP), in which a common set of experiments will be performed using several different models. Some experiments will be performed by the PI, but he will also solicit contributions to the MIP by other researchers. Further research will include an examination of global warming simulations from state-of-the-art climate models in the Coupled Model Intercomparison Project version 5 (CMIP5), as well as perturbed physics sensitivity experiments with a single slab ocean climate model.The educational component of this CAREER project is centered on the development of a flexible climate modeling and analysis package in the Python language. The educational activity is intended to address the lack of computing skills commonly found among undergraduate and graduate students enrolled in atmospheric science departments. Specific tasks are 1) to develop a short introductory course in practical scientific computing in the Python language; 2) to develop a modular Python-based climate modeling and analysis toolkit; and 3) to develop a series of interactive educational modules illustrating fundamental principles of climate and atmospheric science. Several factors motivate the choice of Python as the language of choice, including its inherent modularity, its ability to serve as a "wrapper" for compiled Fortran and C codes, thereby promoting seamless use of established codes, and the numerous visualization and software development tools available for the language. The software to be developed will be open source, freely available online, and well documented. It will consist of a number of simplified dynamical core and process models (for radiative transfer, boundary layer turbulent fluxes, etc.), which can be integrated alone or combined in various ways to form simple a simple climate model. In addition to the on-campus teaching activities, Python-based modules will be developed for use in a summer camp for local high school students.