Feedback attribution of the El Nio-Southern Oscillation-related atmospheric and surface temperature anomalies

Abstract

A feedback attribution analysis is conducted for the ENSO-related atmospheric and surface temperature anomalies in boreal winter. Local temperature anomalies are decomposed into partial temperature changes due to changes in oceanic dynamics/heat storage, water vapor, clouds, atmospheric dynamics, ozone, and surface albedo. It is shown that atmospheric dynamics plays distinctly different roles in establishing the tropical and extratropical temperature response to El Nio. The atmospheric dynamics serves as a primary negative feedback to the tropical (tropospheric) warming by transporting out of the tropics excessive energy production associated with oceanic dynamical forcing. In the northern extratropics, it is the main forcing of atmospheric temperature changes and also modulates surface temperatures via longwave radiative heating and cooling. This provides an alternative view of the "atmospheric bridge" mechanism from the perspective of local energetics and temperature feedback attribution. Substantial tropospheric cooling over the eastern North Pacific is found to be collectively contributed by water vapor, cloud, and atmospheric dynamical feedbacks, driven at least partly by the equatorward shift of the Pacific storm track during El Nio. Polar stratospheric warming (cooling), largely due to atmospheric dynamics, is seen over the Eurasian-Pacific (Atlantic) sector, with ozone feedback contributing significantly to the midstratospheric cooling over the Atlantic sector. Water vapor (atmospheric dynamical) feedback has an overall warming (cooling) effect throughout the tropical troposphere, and cloud feedback cools (warms) the tropical lower to middle (upper) troposphere. Atmospheric dynamics induces stratospheric warming over the entire northern extratropics and drives over northern midlatitudes (high latitudes) a tropospheric cooling (warming) that generally intensifies with altitude. © 2012. American Geophysical Union. All Rights Reserved.