Planetary and synoptic scale interactions in southeast Pacific blocking using Potential Vorticity diagnostics: More evidence for the paucity of wave-wave interactions in Southern Hemisphere blocking

Previous synoptic-dynamic studies of blocking anticyclone life-cycles and the important mechanisms which contribute to the growth and decay these events have shown that large-scale interactions with synoptic-scale transients are important in maintaining blocking events. Early studies suggested that synoptic scale-transients were important to contributing to block formation. Other studies showed that repeated interaction with subsequent cyclones was responsible for the fluctuation in blocking intensities throughout their lifetimes. Few studies have examined the nature of the wave-wave interactions between the synoptic and large-scale events during blocking events. Using Potential Vorticity diagnostics, a blocking event which occurred during July 2001 in the Southeast Pacific Ocean region is examined in order to determine the nature of these interactions. Studies of Northern Hemisphere blocking events have suggested that the interactions between upstream synoptic-scale transients and blocking events are synergistic and mutually beneficial to maintaining the blocking event. Burkhardt and Lupo (2005) suggest that in the Southern Hemisphere, these wave-wave interactions are not mutually beneficial and that blocking structures are the result of the superposition of amplifying transients and a stationary planetary-scale wave. The results of this study will provide further evidence in support of their dynamic model of Southern Hemisphere blocking. This key difference between the dynamics of Northern and Southern Hemisphere blocking events may explain why blocking events are comparatively rare in the Southern Hemisphere.