Pivotal Role of Oceanic Mixed-Layer Depth in Tropical Atlantic Multidecadal Variability  

Speaker:  Jon Robson 

Chair(S): SCOTT OSPREY

wednesday december 04 2024, 13:00

ABSTRACT

Observations have shown that sea surface temperatures in the North Atlantic have swung between periods where they were warming faster or slower than the global average, a phenomenon that has become known as Atlantic Multidecadal Variability (AMV). This variability, especially the changes in the tropical North Atlantic, have been linked to global climate impacts, including changes in Hurricane numbers, the North Atlantic Jet in winter, and rainfall patterns over Europe, North American, and Monsoon regions. However, the mechanisms generating AMV remain unclear. Using experiments where sea surface temperature anomalies are applied in the extratropical North Atlantic in multiple coupled models, we find that tropical AMV is largely a result of changes in oceanic mixed-layer depth. During summer, positive sea surface temperature anomalies in the extratropics weaken the trade winds, resulting in a shallower mixed-layer with reduced heat capacity. Subsequent absorption of climatological shortwave radiation into this shallower mixed-layer then causes tropical sea surface temperatures to warm. Importantly, anomalous surface heat-fluxes make modest contributions to tropical AMV in these experiments.

Using experiments where sea surface temperature anomalies are applied in the extratropical North Atlantic in multiple coupled models, we find that tropical AMV is largely a result of changes in oceanic mixed-layer depth. During summer, positive sea surface temperature anomalies in the extratropics weaken the trade winds, resulting in a shallower mixed-layer with reduced heat capacity. Subsequent absorption of climatological shortwave radiation into this shallower mixed-layer then causes tropical sea surface temperatures to warm. Importantly, anomalous surface heat-fluxes make modest contributions to tropical AMV in these experiments.

The seminar will be broadcast live via Zoom, please follow the link below.

https://ncas.zoom.us/my/ncas.seminar.series  

Password: 619447  

Please note these seminars are intended to be internal to NCAS.  Please do not share details of the link without prior permission.

Please follow these simple guidelines to help make our seminar successful.

1. Please put yourself on mute.

2. If you have a question add it to the chat.  At the end of the talk the Chair will give you the opportunity to ask your question.