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Horizontal structure of winter time 250 mb jet stream variations on the fifteen day time scale
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The horizontal structure of the 250 mb jet stream on the fifteen-day time scale during Northern Hemisphere winter is presented. The winter season is divided into six fifteen-day periods for the 24-year NMC data set. The fifteen-day time-averaged wind speed is used as a basis for calculating the 24 year average and variance fields, and the eigenvectors of the temporal covariance matrix. From the observations of individual fifteen-day average wind speed charts it is apparent that there is clear distinction in variability between the Asian jet stream and the North Atlantic jet stream. The major purpose of this study is characterizing the different variability seen in the two jet streams. In the course of this study, it will be shown that the 250 mb wind data shows a strengthening of the circulation during the most recent 12 years: the number of grid points with wind speed exceeding 45 ms-I shows an increasing trend; and the angular momentum at 250 mb increased about 1% during the recent 12 years. A principal component analysis is conducted to find leading patterns and to seek any coordinated oscillation patterns between the two jet cores. Maximum and minimum centers of the leading eigenvector are located in the North Atlantic area, with secondary extrema in the Northeast Asia and the North Pacific area. A 'Jet Core Ellipse Analysis' is introduced to isolate seasonal transition patterns within winter and to characterize the different variability of the Asian jet core and the North Atlantic jet core. The steadiness of the Asian jet core is contrasted with the higher variability of the North Atlantic jet core during the winter season. The variance of the Asian jet core center position decreases in the middle of winter, while the center position of the North Atlantic jet core moves back and forth between the East coast of North America and the North Atlantic ocean. Greater variability in the horizontal orientation ('poleward tilt') of the core axis is seen for the North Atlantic jet core than the Asian jet core. A ten-day average jet core ellipse analysis is also done to find the sensitivity of averaging period. One noteworthy (:difference between fifteen-day and ten-day average fields is greater jet strength in the Aleutian and Northeast Atlantic regions.
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Includes bibliographical references.
Park, Sangwook (1993). Horizontal structure of winter time 250 mb jet stream variations on the fifteen day time scale. Master's thesis, Texas A&M University. Available electronically from
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