EXTRATROPICALWAVE PACKETS CHARACTERIZATION IN THE SOUTHERN HEMISPHERE SUMMER
Roxana Sagarra y Marcelo Barreiro
Departamento de Ciencias de la Atmósfera, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay.
Instituto Uruguayo de Meteorología.
Manuscript received on May 7th, 2019, on final form on October 24th, 2019.
In this work, a climatological study of the extratropical wave packets during the summer season in the southern hemisphere was conducted. To characterize the wave packets we use the amplitude of the envelope calculated from the meridional velocity field at 300 hPa obtained from NCEP-DOE Reanalysis 2. Using a tracking algorithm, the trajectories of the wave packets were determined and climatological properties such as temporal duration, spatial extension, average velocity of propagation and areas of formation and dissipation were studied. In addition, interannual variability was analysed to determine possible relationships between the activity of the wave packets and the main modes of variability affecting the circulation in the southern hemisphere (Southern Annular Mode and El Niño Southern Oscillation). We found that the duration of the traced packets is concentrated in the range 3-8 days, the spatial extension of the trajectories is concentrated in the range 70o-120o of longitude and the average speed is around 21 m/s. No significant formation regions were observed and a main dissipation region located in the western Pacific with two secondary regions in the western Indian Ocean and western Atlantic were found. The climatological study was complemented with the analysis of a particular case in which significant rainfall accumulations were observed in the southeast of South America under the presence of a localized and coherent wave packet in upper levels that was possible to track for 14 days since its beginning in the western Pacific.