Content area
Full Text
ABSTRACT
The influence of oceanic Ekman heat transport (Q^sub ek^) on air-sea variability associated with ENSO teleconnections is examined via a pair of atmospheric general circulation model (AGCM) experiments. In the mixed layer model (MLM) experiment, observed sea surface temperatures (SSTs) for the years 1950-99 are specified over the tropical Pacific, while a grid of mixed layer models is coupled to the AGCM elsewhere over the global oceans. The same experimental design was used in the Ekman transport/mixed layer model (EKM) experiment with the addition of Q^sub ek^ in the mixed layer ocean temperature equation. The ENSO signal was evaluated using differences between composites of El Niño and La Niña events averaged over the 16 ensemble members in each experiment.
In both experiments the Aleutian low deepened and the resulting surface heat fluxes cooled the central North Pacific and warmed the northeast Pacific during boreal winter in El Niño relative to La Niña events. Including Q^sub ek^ amplified the ENSO-related SSTs by ~ 1/3 in the central and northeast North Pacific, producing anomalies comparable to those in nature. Differences between the ENSO-induced atmospheric circulation anomalies in the EKM and MLM experiments were not significant over the North Pacific. The sea level pressure (SLP) and SST response to ENSO over the Atlantic strongly projects on the North Atlantic Oscillation (NAO) and the SST tripole pattern in observations and both model experiments. The La Niña anomalies, which are stronger than during El Niño, include high pressure and positive SSTs in the central North Atlantic. Including Ekman transport enhanced the Atlantic SST anomalies, which in contrast to the Pacific, appeared to strengthen the overlying atmospheric circulation.
(ProQuest: ... denotes formulae omitted.)
1. Introduction
Even though the wind-driven Ekman transport is confined to a thin surface layer in the ocean, it plays a critical role in the global heat balance. Ekman transport is responsible for a large fraction of the mean ocean heat transport within ~25° of the equator (Kraus and Levitus 1986; Levitus 1987). It is especially effective in the tropics because of the strong trade winds, the low value of the Coriolis parameter, and the large difference between the surface temperature and the temperature of the return flow at depth (when one considers the ocean column...