Collaborative Research: Combined Influence of Snow Cover and El Nino/Southern Oscillation (ENSO) on North African/Mediterranean Temperature and Precipitation

该项目考虑了厄尔尼诺/南方涛动(ENSO)事件和欧亚积雪波动造成的北非和地中海气候异常。研究了两种成因机制，一种涉及Rossby波产生和传播产生的对流层遥相关(“水平”机制)，另一种涉及平流层-对流层相互作用(“垂直”机制)。水平机制假定包括1)从赤道东太平洋向东北传播的正则波列，2)在太平洋上空激发的困在北非-亚洲急流中的超低频Rossby波，并向上传播到地中海地区。垂直机制始于欧亚雪盖的扩大，这导致地表条件变冷，对流层中位势高度降低。这反过来又放大了波1驻波模式，该模式传播到平流层并降低极地涡旋的强度，导致北极或北大西洋涛动的负异常，从而使急流和风暴路径向南移动。急流和风暴路径的南移允许更低的温度入侵中纬度地区，包括地中海地区。这些影响将通过统计分析结合一套模式来检验，这些模式包括Rossby波射线跟踪计算、线性化正压模式、最新的全球大气模式(CAM)和具有良好分辨率的平流层的大气模式(WACCM)。此外，将利用欧亚积雪和ENSO作为地中海季节性降水和地表温度的预报因子，开发并测试一个经验预报方案。由于地中海地区气候变化的农业和其他后果，这项工作具有更广泛的社会影响。更具体地说，经验预测方案将提供给包括哥伦比亚大学国际研究所在内的运营中心。此外，还将开发一个网站，提供有关大气遥相关在产生气候异常方面的作用的公开信息。该项目还将支持和培训一名研究生，从而为这一研究领域未来的科学队伍提供支持。

This project considers the generation of North African and Mediterranean climate anomalies by El Nino/Southern Oscillation (ENSO) events and Eurasian snow cover fluctuations. Two causal mechanisms are examined, one involving tropospheric teleconnections produced by Rossby wave generation and propagation (a "horizontal" mechanism), and the other involving stratosphere-troposphere interactions (a "vertical" mechanism). The horizontal mechanism is hypothesized to consist of 1) a canonical northeastward propagating wave train that emanates from the eastern equatorial Pacific, and 2) an ultra-low frequency Rossby wave that is excited over the Pacific, trapped within the North African-Asian (NAA) jet and propagates upstream to the Mediterranean region. The vertical mechanism begins with an expansion of Eurasian snow cover, which leads to colder surface conditions and lowering of mid-tropospheric geopotential height. This in turn amplifies the wave-1 stationary wave pattern, which propagates into the stratosphere and reduces the strength of the polar vortex, resulting in a negative anomaly of the Arctic or North Atlantic Oscillation, which shifts the jet stream and storm track southward. The southward shift of the jet and storm track allows colder temperatures to invade the middle latitudes, including the Mediterranean region. These influences will be examined through statistical analysis combined with a suite of models including a Rossby wave ray tracing calculation, a linearized barotropic model, a state-of-the-art global atmospheric model (CAM), and an atmospheric model with a well-resolved stratosphere (WACCM). In addition, an empirical prediction scheme will be developed and tested using Eurasian snow cover and ENSO as predictors for seasonal Mediterranean precipitation and surface temperature.The work has societal broader impacts due to the agricultural and other consequences of climate variability in the Mediterranean region. More specifically, the empirical prediction scheme will be provided to operational centers including the International Research Institute at Columbia University. In addition, a website will be developed to provide public information regarding the role of atmospheric teleconnections in producing climate anomalies. The project will also support and train a graduate student, thereby providing for the future scientific workforce in this research area.