Persistence of Cold Wedges in the Somali Current System. Issue 4 (22nd February 2023)

• Record Type: Journal Article
• Authors: Hormann, Verena; Centurioni, Luca R.; Paluszkiewicz, Theresa
• Is Part Of: Geophysical research letters. Volume 50:Issue 4(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-22
• Subjects: descriptive and regional oceanography -- upwelling and convergences -- air/sea interactions -- western boundary currents -- Indian ocean; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL101876
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The Somali Current system in the western Arabian Sea reverses seasonally with the South Asian Monsoon and is associated with localized upwelling cells or cold wedges during the summer southwest monsoon. Drifter trajectories in boreal summer and fall 2014 provide rare observational evidence that the northward Somali Current and associated cold wedges can persist into the boreal fall intermonsoon period. The near‐surface circulation and sea surface temperatures further suggest that the wedge‐like surface signatures may intermittently be capped and then reappear at a later time. Our observations show that the northward Somali Current system rapidly decayed within 1 week after the onset of the winter northeast monsoon and the arrival of a cyclonic eddy at the coast in early November 2014. This eddy may not only have affected regional ocean‐atmosphere interactions but also biogeochemical processes and the marine ecosystem through the transport of water properties and locally induced upwelling. Plain Language Summary: The Indian Ocean rim countries are home to about one third of the global population and depend on rain‐fed agriculture as well as fisheries supported by coastal upwelling systems, which are linked to monsoon variability. A better understanding of regional air‐sea phenomena is therefore needed, and we report here on recent drifter observations in the western Arabian Sea that provide new insights into the persistence of upwelling cells or cold wedges and associated circulation patterns in the southern part of the Somali Current system, which reverses seasonally with the monsoon. Our observations during the 2014 drought year reveal that the northward Somali Current and associated cold wedges can persist into the intermonsoon period following the summer southwest monsoon. The wedge‐like surface signatures in the surface circulation and sea surface temperature may intermittently be capped and then reappear at a later time. During our observational period, the northward Somali Current system of the summer southwest monsoon rapidly decayed within 1 week after the onset of the winter northeast monsoon and the arrival of a mesoscale feature at the coast in early November. The latter may not only have affected regional ocean‐atmosphere interactions but also biogeochemical processes and the marine ecosystem. Key Points: First observational evidence that the northward Somali Current and associated cold wedges may persist into the boreal fall intermonsoon Rapid breakdown of the Somali Current system after the onset of the winter northeast monsoon and the arrival of a cyclonic eddy Persistence of cold wedges and associated circulations may affect air‐sea interactions and biogeochemical processes within the ecosystem