Collaborative Research: Understanding Observed Low Frequency Variability of Sea-Surface Temperature (SST) in the North Atlantic

北大西洋海温在年际和年代际时间尺度上波动，具有不同的特征空间结构。造成这些变化模式的机制仍然知之甚少。各种理论对海洋环流和翻转环流的作用有不同的看法，最重要的是，它们是否涉及海温对大气环流的反馈。这些问题将使用一种新颖的方法来解决；交互式集合耦合全球气候模式（GCM），其中大气模式的集合与海洋模式的单个实现耦合。给定一个足够大的大气模式集合，基本上所有固有的大气噪声通过平均去除，然后海洋由大气强迫驱动，其中只包括大气对海温的确定性响应。表征为“天气噪声”的固有大气变率可以以一种可控的方式重新引入耦合模拟。NCAR社区气候系统模型3 （CCSM3）的集成耦合版本将被实施，并将进行一组6个假设检验实验。“天气噪声”将使用观测和模式输出来评估。后一种情况是所谓的“完美模式”研究，它将用于评估观测和模式误差在利用观测得出的天气噪声中的作用。同样，可以通过在第二个GCM的集合耦合版本中使用来自一个GCM的天气噪声来评估模式与观测差异的重要性。仅模式研究在研究涉及经向翻转环流的变率模式方面是有价值的；因为这些模态发生在很长的时间尺度上，现有的观测记录很难捕捉到。更广泛的影响是使集成耦合的CCSM3可用于社区气候预测以及验证和改进耦合模式。两名研究生将接受耦合气候模式应用方面的培训。

Sea-surface temperatures (SST) in the North Atlantic fluctuate on interannual and on decadal timescales, with different characteristic spatial structures. The mechanisms responsible for these modes of variability remain poorly understood. Theories differ in the roles they ascribe to gyre and overturning circulations in the ocean, and, most importantly, in whether or not they involve feedbacks from the SST onto the circulation of the atmosphere.These issues will be addressed using a novel method; the interactive ensemble coupled global climate model (GCM), in which an ensemble of atmospheric models is coupled to a single realization of the oceanic model. Given a sufficiently large ensemble of atmospheric models, essentially all intrinsic atmospheric noise is removed by averaging, and the ocean is then driven by atmospheric forcing that includes only the deterministic response of the atmosphere to the SST. Intrinsic atmospheric variability denoted "weather noise" can then be reintroduced to the coupled simulations in a controlled way.An ensemble coupled version of the NCAR Community Climate System Model 3 (CCSM3) will be implemented, and a set of six hypothesis-testing experiments will be carried out. "Weather noise" will be evaluated using both observations and model output. The latter case is a so-called "perfect model" study, which will serve to evaluate the role of observational and model errors in using observationally derived weather noise. Similarly, the importance of model differences from observations can be evaluated by using weather noise derived from one GCM in the ensemble coupled version of a second GCM. Model-only studies will be valuable in studying modes of variability involving the meridional overturning circulation; as such modes occur on long timescales not readily captured by the extant observational record.Broader impacts are in making the ensemble coupled CCSM3 available to the community for application to climate prediction and to verifying and improving coupled models. Two graduate students will be trained in the application of coupled climate models.