What Causes the Tropical Atlantic SST Bias in CCSM3?

目前的大气-海洋耦合气候模式不能再现热带大西洋海表温度的年循环，因此不具备模拟或预测热带大西洋气候变率的能力。本项目旨在分析美国国家大气研究中心（NCAR）社区气候系统模式第3版（CCSM3）和第3.5版的混合层热收支，以确定导致这种海温偏差的过程和/或参数化。研究人员将在三个关键区域（东南大西洋、东赤道大西洋和中赤道大西洋以及热带北大西洋）检查当地海洋动力学可能起的作用，并确定和量化外部影响，目的是了解当地大气-海洋反馈过程是否以及如何放大远程信号。具体来说，研究人员将进行一些CCSM3（3.5）实验，包括：(a)固定海温运行的动态大气；(b)具有固定表面通量的动态海洋；(c)完全耦合的大气-海洋运行；(d)大气-海洋耦合运行与区域通量调整。将这些模式运行与观测数据进行比较，将提供一些有用的见解，了解CCSM的海洋和大气分量的固有偏差，以及这些偏差是否以及如何通过耦合过程传递到偏远地区和/或局部放大。通过CCSM3（3.5）测试假设，本研究将增加和完善我们对影响赤道大西洋海温的过程及其对热带大西洋气候变率的更广泛参与的理解。这项工作的结果将被合并到气候模型中，有可能提高对热带大西洋变化的理解，并提高季节到十年的气候预测技能，这将使热带大西洋周围的社会受益。

Current atmosphere-ocean coupled climate models cannot reproduce the annual cycle of tropical Atlantic sea surface temperatures (SSTs) and thus do not have a skill to simulate or to forecast the tropical Atlantic climate variability. This project seeks to analyze the mixed layer heat budget of the National Center for Atmospheric Resesarch (NCAR) community climate system model version 3 (CCSM3) and version 3.5 to identify processes and/or parameterizations that contribute to this SST bias. The investigators will examine the possible role of local ocean dynamics in three key regions (southeastern Atlantic Ocean, eastern and central equatorial Atlantic Ocean, and tropical North Atlantic Ocean), and determine and quantify the external influences, with the goal of understanding if and how local atmosphere-ocean feedback processes amplify the remote signals.Specifically the investigators will perform some CCSM3(3.5) experiments by including (a) dynamic atmosphere with fixed SST run; (b) dynamic ocean with fixed surface flux run; (c) fully coupled atmosphere-ocean run; (d) coupled atmosphere-ocean runs with the regional flux-adjustment. Comparison of these model runs along with the observational data will provide some useful insights on the inherent biases in the ocean and atmospheric components of CCSM, and if and how such biases are transmitted to remote regions and/or locally amplified through the coupling processes. Through testing hypotheses with CCSM3(3.5), this study will increase and refine our understanding of the processes that affect the equatorial Atlantic SST and their broader involvement in tropical Atlantic climate variability. The outcome of the work will be merged into climate models, potentially improving understanding of tropical Atlantic variability and enhancing seasonal-to-decadal climate prediction skill, which will benefit society surrounding the tropical Atlantic.