26 Jul 2023
 | 26 Jul 2023

Intensified Aleutian Low induces weak Pacific Decadal Variability

William James Dow, Christine M. McKenna, Manoj M. Joshi, Adam T. Blaker, Richard Rigby, and Amanda C. Maycock

Abstract. The Aleutian Low drives decadal variability in North Pacific sea surface temperatures (SST), but its role in basin-wide Pacific SST variability is less clear owing to the difficulty of disentangling coupled atmosphere-ocean processes. We apply local atmospheric nudging to isolate the effects of an intense winter Aleutian Low using an intermediate complexity climate model. An intensified Aleutian Low produces a basin-wide SST response with a similar pattern to internally-generated Pacific Decadal Oscillation (PDO). The amplitude of the SST response in the North Pacific is comparable to PDO, but in the tropics and southern subtropics the anomalies induced by the intense Aleutian Low are a factor of 3 weaker. The tropical Pacific warming peaks in boreal spring, though anomalies persist year-round. A heat budget analysis shows the northern subtropical Pacific SST response is predominantly driven by anomalous surface heat fluxes in boreal winter, while in the equatorial Pacific the response is mainly due to meridional heat advection in boreal spring. The propagation of anomalies from the extratropics to the tropics can be explained by the seasonal footprinting mechanism, involving the wind-evaporation-SST feedback. The results show that low frequency variability and trends in the Aleutian Low could contribute to basin-wide anomalous Pacific SST, but the magnitude of the effect cannot explain the full amplitude of the PDO. This finding suggests that external forcing of the Aleutian Low is unlikely to explain observed shifts in the phase of PDO in the late 20th and early-21st centuries.

William James Dow et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1595', Anonymous Referee #1, 22 Aug 2023
  • RC2: 'Comment on egusphere-2023-1595', Anonymous Referee #2, 04 Sep 2023
  • EC1: 'Comment on egusphere-2023-1595', David Battisti, 11 Sep 2023

William James Dow et al.

William James Dow et al.


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Short summary
Changes to sea-surface temperatures in the extra-tropical North Pacific are driven partly by patterns of local atmospheric circulation, such as the Aleutian Low. We show that slowly evolving changes to the Aleutian Low could contribute to changes in temperatures across the equatorial Pacific via the initiation of two mechanisms. The effect, although significant, is unlikely to explain fully the recently observed multi-year shift of a pattern of climate variability across the wider Pacific.