A13A-0301
The Dynamical Influence of Separate Teleconnections from the Pacific and Indian Oceans on the Northern Annular Mode

Monday, 14 December 2015
Poster Hall (Moscone South)
Christopher G Fletcher, University of Waterloo, Waterloo, ON, Canada and Christophe Cassou, CERFACS European Centre for Research and Advanced Training in Scientific Computation, Toulouse Cedex 01, France
Abstract:
This study uses simulations with a coupled ocean-atmosphere GCM to examine the influence of quasi-stationary wave teleconnections from the tropical oceans on the sign and amplitude of wintertime variability of the Northern Annular Mode (NAM). Composites constructed from a 1000-yr pre-industrial control simulation show that increased precipitation in the central/eastern Pacific drives a negative NAM response. In contrast, when isolated from ENSO variability, increased precipitation over the western-central Indian Ocean drives a strong and persistent positive NAM response. The sign and amplitude of the NAM responses are largely explained by opposite linear interference of the wave teleconnections propagating from the tropics. This mechanism is confirmed using a new set of experiments where the tropical ocean is nudged separately over the Pacific and Indian Oceans toward the large amplitude 1997/98 -- 1998/99 ENSO cycle. The phase of the quasi-stationary wave and NAM responses in these two cases are of opposite sign, providing strong evidence that precipitation changes over the Indian Ocean, driven by internal variability and/or in response to climate change, can induce teleconnections that affect the northern extratropics independent of--and with opposite-sign to--those associated with ENSO.