AN OBJECTIVE CLIMATOLOGY OF MOBILE TROUGHS IN THE NORTHERN-HEMISPHERE
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This paper introduces a technique to identify and track midtropospheric mobile troughs. Mobile troughs are objectively identified as maxima in the transport of geostrophic curvature vorticity. A 20year climatology of mobile trough genesis and termination regions is constructed by applying the method to National Meteorological Center 500mb geopotential height data. The objective tracking results are compared to Sanders' (1988) climatology of mobile troughs on the 552 dam contour. The objective method was shown to be more consistent and accurate than Sanders' subjective method, and therefore, determined to be superior in tracking midtropospheric mobile troughs. The mean lifespan of troughs over the 20year dataset was 5.3days and the maximum lifespan was 44days. The geographical shape of the trough genesis and termination regions are associated with the orography. The three preferred genesis regions are northcentral North America, the Mediterranean Sea, and southeast Asia. The three preferred termination regions are the extreme eastern Pacific Ocean, the Mediterranean Sea, and southwest Asia. Trough genesis regions tend to be well upstream of major areas of wintertime surface cyclogenesis. Copyright 1995, Wiley Blackwell. All rights reserved
