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Abstract This study investigates the variability of the Southern Hemisphere super gyre (SHSG), using remotely sensed altimeter measurements, in situ Argo observations, and results from an ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean. Analyses of altimeter data show large trends of sea surface height, and their positive‐negative contrast suggests a strengthening of subtropical gyres in all the three Southern Hemisphere oceans since 1993. Analyses of Argo data and the Estimating the Circulation and Climate of the Ocean estimate indicate that these dynamic signals of southern subtropical gyres extend to at least 2,000 m. The three southern subtropical gyres are interconnected through the Tasman and Agulhas leakages and vary consistently during the period 1993–2016. The Tasman and Agulhas leakages also show an increasing trend of inter‐ocean water exchange with a typical increase of ~2 Sv (1 Sv = 106 m3/s) per decade, indicative of a two‐decade‐long spin‐up of the SHSG. The strengthening and poleward shift of westerly winds are associated with an increasing southern annular mode, which affect the midlatitude and high‐latitude Southern Hemisphere oceans and contribute to the spin‐up of the SHSG.
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Rapid Sea-Level Rise in the Southern-Hemisphere Subtropical Oceans
Abstract The subtropical oceans between 35°-20°S in the Southern Hemisphere (SH) have exhibited prevailingly rapid sea-level rise (SLR) rates since the mid-20thcentury, amplifying damages of coastal hazards and exerting increasing threats to South America, Africa, and Australia. Yet, mechanisms of the observed SLR have not been firmly established, and its representation in climate models has not been examined. By analyzing observational sea-level estimates, ocean reanalysis products, and ocean model hindcasts, we show that the steric SLR of the SH subtropical oceans between 35°-20°S is faster than the global mean rate by 18.2%±9.9% during 1958-2014. However, present climate models—the fundamental bases for future climate projections—generally fail to reproduce this feature. Further analysis suggests that the rapid SLR in the SH subtropical oceans is primarily attributable to the persistent upward trend of the Southern Annular Mode (SAM). Physically, this trend in SAM leads to the strengthening of the SH subtropical highs, with the strongest signatures observed in the southern Indian Ocean. These changes in atmospheric circulation promote regional SLR in the SH subtropics by driving upper-ocean convergence. Climate models show systematic biases in the simulated structure and trend magnitude of SAM and significantly underestimate the enhancement of subtropical highs. These biases lead to the inability of models to correctly simulate the observed subtropical SLR. This work highlights the paramount necessity of reducing model biases to provide reliable regional sea-level projections.
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- Award ID(s):
- 1935279
- PAR ID:
- 10580671
- Publisher / Repository:
- Duan_etal_jclim2021.pdf
- Date Published:
- Journal Name:
- Journal of Climate
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 1 to 55
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/JCLI-D-21-0248.1
