[OANNES Foro] Influence of Arctic sea-ice variability on Pacific trade winds

[Mario Cabrejos]

PNAS 

January 27, 2020 

 <https://doi.org/10.1073/pnas.1717707117>
https://doi.org/10.1073/pnas.1717707117 

Influence of Arctic sea-ice variability on Pacific trade winds

Charles F. Kennel and Elena Yulaeva

Significance

By 20th-century standards, the Central Pacific trade winds that drive the El
Nino-Southern Oscillation feedback system to instability have been unusually
strong in the 21st century. The annual summer melts of Arctic sea ice are up
to twice as large in area as in the 20th century. Arctic sea ice, upper
atmospheric circulation, surface wind, and sea-surface temperature data
provide evidence that upper troposphere transport processes connect the
increased summer losses of Arctic sea ice to the trade-wind and Central
Pacific El Nino events characteristic of the present climate state. These
results add to the evidence that loss of Arctic sea ice is having a major
impact on climatic variability around the world.

Abstract

A conceptual model connecting seasonal loss of Arctic sea ice to midlatitude
extreme weather events is applied to the 21st-century intensification of
Central Pacific trade winds, emergence of Central Pacific El Nino events,
and weakening of the North Pacific Aleutian Low Circulation. According to
the model, Arctic Ocean warming following the summer sea-ice melt drives
vertical convection that perturbs the upper troposphere. Static stability
calculations show that upward convection occurs in annual 40- to 45-d
episodes over the seasonally ice-free areas of the Beaufort-to-Kara Sea arc.
The episodes generate planetary waves and higher-frequency wave trains that
transport momentum and heat southward in the upper troposphere. Regression
of upper tropospheric circulation data on September sea-ice area indicates
that convection episodes produce wave-mediated teleconnections between the
maximum ice-loss region north of the Siberian Arctic coast and the
Intertropical Convergence Zone (ITCZ). These teleconnections generate
oppositely directed trade-wind anomalies in the Central and Eastern Pacific
during boreal winter. The interaction of upper troposphere waves with the
ITCZ air-sea column may also trigger Central Pacific El Nino events.
Finally, waves reflected northward from the ITCZ air column and/or generated
by triggered El Nino events may be responsible for the late winter weakening
of the Aleutian Low Circulation in recent years.

 

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