Regional Features of the 20-30 Day Periodic Behavior in the Southern
Hemisphere Summer Circulation
Abstract
The Southern Hemispheric (SH) storm tracks exhibit a robust
intraseasonal periodicity of 20-30 days as the leading mode of
zonal-mean eddy kinetic energy. To what extent this hemispheric-scale
mode of variability translates to smaller scales remains debated. This
work studies the regional features of SH storm tracks through the
filtered variance of local finite-amplitude wave activity. While the
synoptic variance is zonally elongated over the storm track, we find a
strong enhancement of intraseasonal variability within the South Pacific
with a minimum strength of the storm track. This enhanced region is
marked with 20-30 day periodic behavior of local wave activity and
precipitation and is driven by enhanced variability of low-level eddy
heat flux on the same timescale. The local nature of 20-30 day
periodicity offers a potential source of intraseasonal predictability
for weather analysts and forecasters.