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20世纪经历了最明显的变暖趋势。许多极端气候事件受到大西洋海洋条件的影响。因此，必须对大西洋气候进行精确的模拟，以便能够对周围大陆地区的未来气候作出可靠的预测。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显示出严重的偏差。一个臭名昭著的例子是纳米比亚和安哥拉海岸附近持续温暖的海面温度偏差至少6°C。这项研究的目的是调查这种偏差的原因，这将最终导致大西洋地区未来气候变化的模拟和预测的重大改进。智力优势：该项目将探索海洋和大气偏差，以及海洋-大气耦合系统的偏差放大。将从海洋观测、海洋再分析产品、IPCC模式模拟和涡旋解析区域海洋模拟中分析和确定海洋偏倚的来源。同样，将利用大气再分析数据和对流解析区域大气模式模拟来评估大气偏差。海洋-大气相互作用在放大海洋或大气偏倚中的作用将通过高分辨率耦合区域气候模式（CRCM）模拟来检验。高分辨率（高达3公里）区域气候模式的使用将允许诸如海洋中尺度涡旋、锋面和南部非洲西海岸外的上升流动力学等过程，以及大气对流和陡地形效应，从而将由于与亚网格尺度过程参数化相关的不确定性而导致的模式系统误差最小化。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。这项研究将利用一系列精细的时间和空间分辨率数据集，这些数据集是由最近在大西洋地区的密集观测项目产生的。此外，该项目将与在该研究区域启动的两个主要欧洲研究项目同时启动：由勃兰特领导的德国项目“西南非洲沿海上升流系统和本格拉Niño”（SACUS），以及由基恩利赛德领导的欧盟项目“加强热带大西洋气候及其影响的预测”（前言）。这两个项目都将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建模相结合，这可能会在解决热带大西洋偏倚问题方面取得新的突破。更广泛的影响：这项研究将增强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是在耦合器（CPL7）软件框架内开发的，该软件是国家大气研究社区地球系统模型中心（CESM）的一部分。这个框架允许在CESM和CRCM之间轻松地传递参数化，以及CESM和CRCM之间潜在的部分耦合。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界。减少气候模式偏差的研究结果将反馈给社区模式开发活动。该项目将资助德克萨斯农工大学（TAMU）的一名研究生和一名博士后，并为所有参与其中的年轻科学家提供宝贵的专业发展机会，包括副pi Patricola。

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.