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

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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.