An assessment of three automatic depression tracking schemes

The performance of three automatic depression tracking schemes developed by Terry & Atlas (1996), Murray C Simmonds (1991a) and Konig et al. (1993) wh en applied! over one month are assessed. The schemes respectively identify depressions by (a) locating the innermost closed contour in a PMSL field (b ) finding maximal in the curvature in a bi-cubic Spline fitted to the PMSL data and (c) performing a gridpoint search to identify a minimum in a PMSL field The largest number of depressions was found by the Murray and Simmond s scheme, with the Atlas and Terry scheme finding the least. The Murray and Simmonds scheme also found the largest number of tracks, with the other tw o having comparable numbers of tracks. Two possible explanations for the di fferences in the number of tracks are considered. Firstly, the cdse where o ne or more centres identified by one scheme as corresponding to a single tr ack are not found by the other schemes. Secondly, the cdse where a Single t rack found by one scheme is split into two or more tracks by the other sche mes. All three techniques had a similar latitude of cyclogenesis, although the Atlas and Terry and Konig et al. schemes found more lows dt high latitu des as a result of using data On a latitude/longitude grid. The longest mea n track length was found with the Konig et al. scheme. A comparison of the PMSL fields with satellite imagery shows that the major NWP centres have tr ouble producing reliable analyses around the Antarctic because of the lack of data.