An assessment of three automatic depression tracking schemes
The performance of three automatic depression tracking schemes developed by Terry & Atlas (1996), Murray & Simmonds (1991a) and Konig et al. (1993) when applied over one month are assessed. The schemes respectively identify depressions by (a) locating the innermost closed contour in a PMSL field, (b) finding maxima in the curvature in a bi-cubic spline fitted to the PMSL data and (c) performing a grid point search to identify a minimum in a PMSL field. The largest number of depressions was found by the Murray and Simmonds 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 two having comparable numbers of tracks. Two possible explanations for the differences in the number of tracks are considered. Firstly, the case where one or more centres identified by one scheme as corresponding to a single track are not found by the other schemes. Secondly, the case where a single track found by one scheme is split into two or more tracks by the other schemes. All three techniques had a similar latitude of cyclogenesis, although the Atlas and Terry and Konig et al. schemes found more lows at high latitudes as a result of using data on a latitude/longitude grid. The longest mean 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 trouble producing reliable analyses around the Antarctic because of the lack of data.