26.10.2020: Online Ocean Circulation and Climate Dynamics Colloquium

online 11 am
Webex meeting room: https://geomar.webex.com/geomar/j.php?MTID=m91e1409f7e74f4fdd11c5a3432ffa767

Meeting number (access code): 137 681 5166
Meeting password: BvVzYku4J35

Authors: Mathias Zeller, Shayne McGregor, Antonietta Capotondi, Erik van Sebille, Paul Spence

Understanding mechanisms of tropical Pacific decadal variability (TPDV) is of high importance for differentiating between natural climate variability and human induced climate change as this region sustains strong global teleconnections. Here, we use an ocean general circulation model along with a Lagrangian tracer simulator to investigate the advection of density compensated temperature anomalies ("spiciness mechanism") as a potential contributor to TPDV during the 1980-2016 period. We show two prominent cases where remotely generated spiciness anomalies are advected to the equatorial Pacific, impacting subsurface temperature. The relative contribution of Northern versus Southern Hemisphere prominence and/or interior versus western boundary pathways depends on the specific event. The anomalously warm case largely results from advection via the Southern hemisphere interior (65%), while the anomalously cold case largely results from advection via the Northern hemisphere western boundary (48%). The relatively slow travel times from the subtropics to the equator (>4 years) suggests that these spiciness anomalies underpin a potentially predictable contribution to TPDV. Once at the equator spiciness anomalies upwell and interact with the atmosphere. However, a quantitative assessment of the impact of spiciness anomalies on the equatorial heat budget is still lacking. Using the same ocean general circulation model, we examine the impact of spiciness anomalies on the vertical heat advection into the equatorial near-surface layer. We therefore perform an equatorial Pacific mixed layer heat budget analysis with a focus on the contribution of both locally and remotely generated spiciness anomalies. Our results indicate that spiciness anomalies account for 30-60% of the vertical heat advection. The major impact originates from locally generated spiciness anomalies. However, remotely generated spiciness anomalies also have an impact on the equatorial heat budget making up 14-23% of the variance, with the impact decreasing towards the western equatorial Pacific. Our results further suggest that the impact of remotely generated spiciness anomalies is considerably larger during La Niña phases as opposed to El Niño phases.

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