Decadal Influence of the Solar Cycle (DISC)

虽然由于温室气体水平的增加，预计全球气候在下一个世纪将变暖，但在今后十年左右的时间里，区域变化很可能受气候系统非受迫自然变率的支配。其中一些自然变异可能可以提前几个月甚至几年预测，因为它与相对缓慢的过程有关，特别是海洋中的过程（厄尔尼诺现象、温盐环流的波动和海洋热含量的大规模异常）。长期变化的另一个潜在来源是众所周知的太阳输出的11年变化，但信号如何到达表面的机制还没有得到很好的理解，正因为如此，它在用于十年预测的气候模型中没有得到很好的体现。在11年周期内太阳总辐照度的百分比变化非常小，但是紫外线的变化要大得多，这会影响平流层温度和臭氧的产生。已经提出了各种机制来解释这种平流层太阳信号如何将其影响扩展到地面，包括通过大气环流变化的放大机制。观测分析表明，地面对太阳变化的响应是区域性的。围绕欧洲上空观测到的信号一直存在争议，但最近对欧洲上空长期观测记录的分析证实了一个滞后3-4年的强统计显著信号。气候模式，包括Hadley中心的HadGEM模式，能够捕捉平流层上部对紫外线变化的反应，但不能再现平流层下部观测到的信号，也不能再现欧洲上空观测到的滞后信号，HadGEM模式在紫外线变化特别大的情况下进行的敏感性试验能够再现信号的滞后性质，因此显示出它有能力再现信号，但地面响应幅度仍然太弱，这表明还有很大的改进余地，这将导致十年期预报的改进。该提案的主要目的是改进HadGEM气候模型中太阳对地球表面影响机制的表示，以便改进使用气象局DePreSys业务十年预报模型的预报。该项目将使用HadGEM模型和一个更简单的模型来广泛测试各种机制，特别侧重于改进通过平流层加热异常将太阳信号传递到地面的机制的代表性，以及一个涉及北大西洋大气-海洋耦合的地面放大机制。将通过比较选定年份的重新预报（后报）结果，特别注意大西洋/欧洲部分的改进，来检验HadGEM模型由此产生的改进。该项目将由牛津大学的研究人员进行，他们将进行HadGEM调查，帝国理工学院将进行机械模型调查。英国气象局的项目合作伙伴将提供广泛的支持，他们将密切参与HadGEM实验的解释和DePreSys预报系统改进的实施/测试，基尔大学的项目合作伙伴将提供太阳光谱强迫方面的建议，并有助于在其他主要气候模型的背景下解释结果。

Although global climate is expected to warm over the next century in response to increasing levels of greenhouse gases, regional changes over the next decade or so are likely to be dominated by unforced natural variability of the climate system. Some of this natural variability is potentially predictable months or even years in advance because it is related to relatively slow processes, especially those in the ocean (El Niño, fluctuations in the thermohaline circulation, and large-scale anomalies of ocean heat content). Another potential source of long-term variability comes from the well-known 11-year solar variations in the Sun's output but the mechanisms for how the signal reaches the surface is not well understood and, because of this, it is not well represented in climate models used for decadal predictions.The percentage variation in total solar irradiance over an 11-yr cycle is very small, but the variation in the UV is much larger and this can impact stratospheric temperatures and ozone production. Various mechanisms have been proposed to explain how this stratospheric solar signal may extend its influence to the surface, including amplifying mechanisms through atmospheric circulation changes. Analysis of observations show that the surface response to solar variability is regional. There has been controversy surrounding the observed signal over Europe, but recent analysis of long-term observational records over Europe have confirmed a strong statistically significant signal at lags of 3-4 years. Climate models, including the Hadley Centre HadGEM model, are able to capture an upper stratospheric response to changing UV, but do not reproduce the observed signal in the lower stratosphere nor the observed lagged signal over Europe.Sensitivity tests with the HadGEM model with an exceptionally large UV change was able to reproduce the lagged nature of the signal, thus showing some promise for its ability to reproduce the signal, but the surface response amplitude is still much too weak, suggesting that there is room for significant improvements which should lead to improved decadal forecasts. This prime aim of the proposal is to improve the representation of mechanisms of solar influence on the Earth's surface in the HadGEM climate model so that forecasts using the Met Office DePreSys operational decadal forecast model can be improved. The project will employ both the HadGEM model and a simpler model for extensive testing of mechanisms, with a particular focus on improving the representation of those mechanisms that transfer the solar signal to the surface via stratospheric heating anomalies and a surface amplifying mechanism that involves atmosphere-ocean coupling in the North Atlantic. The resulting improvements to the HadGEM model will be tested by comparing results from re-forecasts (hindcasts) of selected years, with particular attention to improvements in the Atlantic / European sector. The project will be performed by researchers at Oxford University who will carry out the HadGEM investigations and Imperial College who will perform the mechanistic model investigations. Extensive support will be provided by Project Partners at the Met Office, who will be closely involved in the interpretation of the HadGEM experiments and implementation / testing of improvements in the DePreSys forecast system and a Project Partner at Kiel University who will advise on solar spectral forcing and contribute to interpretation of results in the context of other major climate models.