An objective climatology of mobile troughs in the northern hemisphere

Abstract

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 20-year climatology of mobile trough genesis and termination regions is constructed by applying the method to National Meteorological Center 500 mb 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 mid-tropospheric mobile troughs. The mean lifespan of troughs over the 20-year dataset was 5.3 days and the maximum lifespan was 44 days. The geographical shape of the trough genesis and termination regions are associated with the orography. The three preferred genesis regions are north-central 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.