Understanding Causes of Climate Model Biases in the Southeastern Tropical Atlantic

最近的研究表明，在所有热带海洋中，大西洋在世纪经历了最明显的变暖趋势。许多极端气候事件都受到大西洋海洋状况的影响。因此，必须对大西洋气候进行准确的模拟，以便能够对周围大陆地区的未来气候做出可信的预测。不幸的是，当前的模型，包括政府间气候变化专门委员会（IPCC）使用的模型，在模拟热带大西洋气候时表现出严重的偏差。一个臭名昭著的例子是纳米比亚和安哥拉沿海持续温暖的海面温度偏差至少为6°C。 这项研究的目的是调查这种偏见的原因，这将最终导致重大改进的模拟和预测未来的气候变化在大西洋sector.Intellectual Merit：这个项目将探讨海洋和大气的偏见，以及放大的偏见从耦合的海洋-大气系统。 海洋偏差的来源将从海洋观测、海洋再分析产品、IPCC模式模拟和涡旋分辨区域海洋模拟中分析和识别。 同样，将利用大气再分析数据和对流分辨区域大气模型模拟来评估大气偏差。 将从高分辨率耦合区域气候模式（CRCM）模拟中研究海洋-大气相互作用在放大海洋或大气偏差方面的作用。 使用高分辨率（最高3公里）区域气候模型将能够模拟海洋中尺度涡旋、锋面和南部非洲西海岸外的上升流动态以及大气对流和陡峭地形效应等过程，从而将最大限度地减少因次网格尺度过程参数化的不确定性而造成的模型系统误差。这种建模方法将从其他海洋盆地中分离出偏差的来源，并将有助于查明大西洋盆地内偏差的原因。这项研究将利用最近在大西洋地区密集观测方案产生的一系列时间和空间分辨率很高的数据集。此外，该项目将与欧洲在研究区域启动的两个主要研究项目同时进行：由Brandt领导的德国项目“西南非洲沿海上升流系统和本格拉厄尔尼诺现象”（SACUS）和由Keenlyside领导的欧盟项目“加强对热带大西洋气候及其影响的预测”（PREFACE）。 这两个项目都将在沿着南部非洲海岸产生新的观测阵列。与欧洲同事的密切合作将使他们的新观测与美国的详细模拟相结合，这可能会导致解决热带大西洋偏差问题的新突破。更广泛的影响：这项研究将提高我们对预测全球气候变化对大西洋地区影响的不确定性的理解，这对该地区的国家具有巨大的社会经济影响。CRCM正在耦合器（CPL 7）软件的框架内开发，该软件是国家大气研究中心社区地球系统模型（CESM）的一部分。这一框架便于在CESM和CRCM之间转移参数，并在CESM和CRCM之间实现潜在的部分耦合。 我们设想CRCM将成为一个社区建模工具，并提供给更广泛的气候研究社区。这项关于减少气候模型偏差的研究结果将反馈给社区模型开发活动。该项目将支持一名研究生和一名博士后在得克萨斯州农工大学（TAMU），并提供宝贵的专业发展，为所有年轻的科学家参与，包括共同PI帕特里科拉。

Recent studies have revealed that among all the tropical oceans, the Atlantic has experienced the most pronounced warming trend over the 20th century. Many extreme climate events are influenced by oceanic conditions over the Atlantic. It is therefore imperative to have accurate simulations of the Atlantic Ocean climate to be able to make credible projections of future climate in the surrounding continental regions. Unfortunately, current-generation models, including those used by the Intergovernmental Panel on Climate Change (IPCC), exhibit severe biases in their simulations of tropical Atlantic climate. An infamous example is a persistent warm sea surface temperature bias of at least 6°C off the coast of Namibia and Angola. This research aims at investigating the causes of this bias which will ultimately lead to major improvements in the simulation and projection of future climate changes within the Atlantic sector.Intellectual Merit: This project will explore oceanic and atmospheric biases, as well as amplification of biases from the coupled ocean-atmosphere system. The sources of oceanic biases will be analyzed and identified from oceanic observations, ocean reanalysis products, IPCC model simulations, and eddy resolving regional ocean simulations. Similarly, atmospheric biases will be evaluated using atmospheric reanalysis data and convection-resolving regional atmospheric model simulations. The role of ocean-atmosphere interactions in amplifying the oceanic or atmospheric biases will be examined from high-resolution coupled regional climate model (CRCM) simulations. The use of high-resolution (up to 3 km) regional climate models will allow processes such as oceanic mesoscale eddies, fronts and upwelling dynamics off the west coast of southern Africa, as well as atmospheric convection and steep orography effects, and thus will minimize model systematic errors due to uncertainties associated with parameterizations of subgrid-scale processes. This modeling approach will isolate sources of the biases from other ocean basins and will help to pinpoint the causes of the biases within the Atlantic basin. The study will utilize an array of fine temporal and spatial resolution data sets produced by recent intense observational programs within the Atlantic sector. Furthermore, the project will coincide with the launch of two major European research projects in the study region: a German project "Southwest African Coastal Upwelling System and Benguela Niño" (SACUS) led by Brandt, and an EU project "Enhancing prediction of tropical Atlantic climate and its impacts" (PREFACE) led by Keenlyside. Both of these projects will generate new arrays of observations along the southern Africa coast. Close collaboration with the European colleagues will allow their new observations to be combined with US-based detailed modeling that will likely lead to new breakthroughs in solving tropical Atlantic bias problems.Broader Impacts: This research will enhance our understanding of the uncertainties in projecting impacts of global climate change in the Atlantic region, which has enormous socio-economic implications for countries in the region. The CRCM is being developed within the framework of the Coupler (CPL7) software that is part of the National Center for Atmospheric Research Community Earth System Model (CESM). This framework allows easy transfer of parameterizations between CESM and the CRCM, and potential partial coupling between the CESM and the CRCM. We envision that the CRCM will become a community-modeling tool and be made available to the broader climate research community. Findings from this study on reducing climate model biases will feedback to community model development activities. The project will support one graduate student and one postdoc at Texas A&M University (TAMU) and provide valuable professional development for all young scientists involved, including Co-PI Patricola.