Statistical Relationships Between the Subtropical Jet Stream and Extra-tropical Cyclones

Friday, December 16, 2016 - 08:00
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Extra-tropical cyclones(ETCs) and associated fronts bring much of the precipitation in California during winter. It was previously suggested that inter-model spread of the California precipitation in future projection under global warming could be largely explained by the inter-model spread of ETC activities, with a correlation of 0.85. ETCs are believed to be steered by the jet stream, but a definitive relationship between the frontal precipitation in California and the subtropical jet through cyclone activities is yet to be established . Using output from CCSM4 historical and future runs, we investigate how California precipitation changes are tied to changes in ETC characteristics, and how the jet stream in turn influence the ETCs. The strength, the latitudinal position, the width of the jet stream are studied against the spatial distribution and the life span of the ETCs. We utilize the parallel toolkit for extreme climate analysis (TECA) to track both the jet stream and the ETCs and to analyze statistics relating the two. We rigorously define ETCs by its pressure, vorticity, and preferable direction of travel, and also track the jet stream in the 3-D space by its wind speed and westerly component. This study brings new insights into the dynamic relationship between midlatitude storm tracks and the jet stream.

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