Climatology of tropopause folds over a European Arctic station (Esrange)

Abstract

Eleven years (September 1996 to August 2007) of continuous measurements of three-dimensional wind and backscattered signal strength observed with Esrange Radar (ESRAD) have been utilized to study the annual and interannual variation of tropopause folds over an Arctic station. Two typical tropopause fold events (one is associated with a streamer type of system and the other with a cutoff low) are selected and are characterized with the help of synoptic charts and potential vorticity (PV) analysis. Typical characteristics of radar parameters during the passage of folds are identified, such as the sudden rise in the tropopause altitude, high-reflectivity layer sloping downward from the tropopause beneath the jet stream, and intensification of the jet stream. These characteristics are utilized to discern the tropopause fold in the radar data. The climatology of tropopause folds exhibits a pronounced annual cycle with a large number of folds in winter and fewer in summer. The annual cycle of folds is more or less similar in all the years; however, significant interannual variation is observed with winter periods exhibiting maximum interannual variability. The climatology of folds and its annual cycle are compared and contrasted with similar climatological studies available in the literature. The differences in the climatologies are discussed in light of differences in the algorithms and the spatial variability of fold frequency.