The Structure, Evolution, and Life Cycles of Intraseasonal Fluctuations of the North Pacific Jet Stream

这项工作旨在通过结合统计、天气气候学和个案研究分析，大幅增加我们对冬季太平洋急流可变性的了解。高空急流作为天气尺度天气系统与大尺度环流交界处的主要现象，对区域气候具有特别强的制约作用。尽管冬季太平洋急流对太平洋盆地内外的合理天气和大范围环流都有重大影响，但目前对其季节内变化的了解还远远不够。在之前的工作中，该团队已经确定了这种可变性的两种主要模式。在该项目中，该小组将确定太平洋急流变化的主要模式之间的首选过渡；这一结果将为建造与每一种首选过渡有关的全盆地结构、演变和天气特征的综合资料提供信息。利用相空间分析扩展急流收缩气候学，研究西伯利亚/欧亚地区对流层低层冷空气的面积范围与太平洋急流的纬向范围之间的关系。由于太平洋急流是极地急流和副热带急流的混合体，再分析数据也将被用来检验这两个成分在已确定的急流缩回案例中的行为，作为将缩回事件的种群分开的第一步，这些缩回事件分别是由温带和热带变率强迫的。最后，为了更好地了解它们背后的大尺度和天气尺度动力学，将使用NCAR天气研究和预报(WRF)模式对两个具有代表性的急流收缩案例进行详细的案例研究，这些案例利用选定案例的精细数值模拟结果进行。该项目将深入了解冬季太平洋喷流的可变性；这将对夏威夷和西海岸的预测有所改进。因此，这一项目的广泛影响是巨大的。

The work aims to substantially increase our knowledge of wintertime Pacific jet variability through a combination of statistical, synoptic-climatological and case study analyses. As the primary phenomenon at the interface between synoptic-scale weather systems and the large-scale circulation, upper tropospheric jets are particularly strong governors of regional climate. Despite the substantial influence that the wintertime Pacific jet has on both sensible weather and large-scale circulation within and beyond the Pacific basin, current understanding of its intraseasonal variability is far from complete. In prior work the team has identified two leading modes of this variability. In this project the team will identify preferred transitions between the leading modes of variability of the Pacific jet; the results of this will inform construction of composites of the basin-wide structure, evolution and weather features associated with each species of preferred transition. Using the phase space analysis to expand the jet retraction climatology, the relationship between the areal extent of lower tropospheric cold air over the Siberia/Eurasia sector and the zonal extent of the Pacific jet will be examined. Since the Pacific jet is a hybrid of the polar and subtropical jets, reanalysis data will also be used to examine the behavior of these two components in identified cases of jet retraction as a first step toward segregating the population of retraction events into those forced primarily by extratropical and tropical variability, respectively. Finally, in order to better understand their underlying large- and synoptic-scale dynamics, detailed case study analyses of two representative cases of jet retraction employing output from fine-scale numerical simulations of the selected cases will be undertaken using the NCAR Weather Research and Forecasting (WRF) model. This project will shed insights into wintertime Pacific jet variability; this has implications for improved prediction for the state of Hawaii as well as the west coast. Thus the broader impacts of this project are substantial.