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

北大西洋海面温度(SST)在年际和年代际时间尺度上波动，具有不同的空间结构特征。造成这些可变性模式的机制仍然知之甚少。不同的理论归因于海洋环流和颠覆环流的作用，最重要的是，它们是否涉及SST对大气环流的反馈。这些问题将使用一种新的方法来解决；交互式系综耦合全球气候模式(GCM)，其中一组大气模式耦合到海洋模式的单一实现。给出一个足够大的大气模式集合，基本上所有固有的大气噪声都通过平均消除，然后海洋由大气强迫驱动，其中只包括大气对SST的确定性响应。将实施NCAR社区气候系统模式3(CCSM3)的集合耦合版本，并将进行一组六个假设检验实验。“天气噪声”将使用观测值和模型输出进行评估。后一种情况是所谓的“完美模型”研究，它将用于评估观测误差和模型误差在使用观测得出的天气噪声方面的作用。类似地，可以通过在第二个GCM的集合耦合版本中使用来自一个GCM的天气噪声来评估来自观测的模型差异的重要性。只有模式研究对于研究涉及经向翻转环流的变率模式将是有价值的，因为这种模式发生在现有观测记录很难捕捉到的长时间尺度上。更广泛的影响是使集合耦合的CCSM3可供社区应用于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型应用方面的培训。

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.