Upper-level extratropical disturbances over the low-latitude North Atlantic: Generation mechanisms and predictability

穿透到低纬度的高层对流层外扰动是北大西洋上空天气尺度环流的一个常见特征，并可能参与强降水或撒哈拉沙尘暴等重大天气事件。线性Rossby波理论成功地解释了许多气候特征，但控制个别扰动演变的因素仍然没有得到很好的理解。以前关于这一问题的工作是基于对观测数据的统计分析或采用数值模型的案例研究。拟议的项目是第一个系统地探讨长期业务集合预报数据的巨大动力学信息内容。由于每个集合成员是一个可能的天气演变的物理现实的实现，这种方法可以直接评估不同因素的相对重要性，如斜压能量转换或潜热释放。其他目标是概率预报验证、从集合扩散中估计可预报性和评估对高影响天气预报的影响。这一项目的结果将促进人们更好地从物理上了解北大西洋上空热带地区受到的外来影响，并揭示最先进的业务系统成功预测低纬度扰动及其影响的能力。

Upper-level extratropical disturbances penetrating to low latitudes are a frequent feature of the synoptic-scale circulation over the North Atlantic and can be involved in significant weather events such as heavy precipitation or Saharan dust outbreaks. Linear Rossby-wave theory successfully explains many climatological characteristics, but the factors controlling the evolution of individual disturbances are still not well understood. Prior work on this matter is based on statistical analyses of observational data or case studies with numerical models. The proposed project is the first that systematically explores the huge dynamical information content of long-term operational ensemble prediction data. Since every ensemble member is a physically realistic realisation of a possible synoptic evolution, this approach allows a direct assessment of the relative importance of different factors such as baroclinic energy conversion or latent heat release. Other objectives are a probabilistic forecast validation, the estimation of predictability from the ensemble spread and the assessment of implications for high-impact weather forecasts. The results of this project will foster a better physical understanding of extratropical influences on the Tropics over the North Atlantic and unveil the ability of state-of-the-art operational systems to successfully predict low-latitude disturbances and their impacts.