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

该项目考虑厄尔尼诺/南方涛动事件和欧亚积雪波动造成的北非和地中海气候异常。两个因果机制进行检查，一个涉及对流层遥相关产生的Rossby波的产生和传播（“水平”机制），和其他涉及平流层对流层的相互作用（“垂直”机制）。 水平机制被假设为包括1）一个典型的东北向传播波列，从赤道东太平洋，和2）一个超低频Rossby波，在太平洋上激发，被困在北非-亚洲（NAA）急流和上游传播到地中海地区。垂直机制开始于欧亚积雪的扩大，这导致更冷的地面条件和对流层中层位势高度的降低。这反过来又放大了波-1定常波模式，它传播到平流层，降低了极地涡旋的强度，导致北极或北大西洋涛动的负异常，使急流和风暴轨迹向南移动。急流和风暴路径的南移使较冷的温度侵入中纬度地区，包括地中海地区。 这些影响将通过统计分析结合一系列模型来检查，包括Rossby波射线追踪计算、线性正压模型、最先进的全球大气模型（CAM）和具有良好分辨率的大气模型平流层（WACCM）。 此外，还将利用欧亚积雪和厄尔尼诺/南方涛动现象作为地中海季节性降水和地表温度的预测因子，制定和检验经验预测方案，由于地中海区域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业务中心。 此外，还将开发一个网站，提供关于大气遥相关在产生气候异常方面的作用的公共信息。 该项目还将支持和培训一名研究生，从而为这一研究领域的未来科学工作者提供支持。

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.