Interactions between anomalous wave activity and a strong El Nino
Sam Lillo & David Parsons
University of Oklahoma
10 Nov, 1:10 pm in 2155
Abstract:
The winter of 2015-16 featured a strong El Nino with enhanced tropical
convection in the central Pacific, forcing classic anomalous Hadley
cell and Walker circulations. In addition, poleward Rossby wave
dispersion. Meanwhile, the North Pacific was characterized by
significant synoptic-scale Rossby wave activity emerging from Asia,
including multiple wave packets tracking around the globe during
February and March. The interaction of one of these packets with the
ENSO-driven subtropical anticyclone resulted in a large wavebreak over
the East Pacific, leading to the deepening of a trough over Mexico of
unprecedented amplitude on 10 March 2016. This trough had significant
ramifications at the surface, including an intense cold wave across
central Mexico and snow as far south as Guadalajara.
Overall, short-wave Rossby wave activity was more prevalent this past
winter across the extratropical Pacific than during past strong El Nino
winters. The background flow in the mid-latitudes diverged from
canonical strong Nino conditions, with a well-defined waveguide north
of the typical zone of refraction in the subtropical jet. The waveguide
acted to trap poleward-propagating wave activity from the tropics and
maintain the coherence of Rossby wave packets in the mid-latitude jet.
Motivated by these observations, we explore implications in high impact
weather, as well as its predictability during this past winter.