South Indian Ocean Rossby Waves. Issue 5 (20th October 2018)

• Record Type: Journal Article
• Authors: Jury, Mark R.
• Is Part Of: Atmosphere-ocean. Volume 56:Issue 5(2018)
• Page Start: 322
• Page End: 331
• Publication Date: 2018-10-20
• Subjects: South Indian Ocean -- Rossby waves; Ocean-atmosphere interaction -- Canada -- Periodicals; Ocean-atmosphere interaction -- Periodicals; Oceanography -- Canada -- Periodicals; Oceanography -- Periodicals; Meteorology -- Canada -- Periodicals; Meteorology -- Periodicals; 551.5246
• DOI: 10.1080/07055900.2018.1544882
• Languages: English
• ISSNs: 0705-5900

Abstract

ABSTRACT: South Indian Ocean Rossby waves (SIO-RW) are identified in the Global Ocean Data Assimilation System (GODAS) 1.5–7 yr filtered sea surface height (SSH) time series. There is a persistent three-year oscillation in the 5°–15°S latitude band from 55° to 85°E. Field correlations show little coupling at 90°E, but as the SIO-RW undulates westward at approximately 0.19 m s −1 across the mid-basin, a northwest–southeast axis of warm sea surface temperatures (SSTs) and deep convection forms. Many teleconnections in earlier work are confirmed: interannual pulses of zonal wind in the eastern basin trigger the SIO-RW via anticyclonic wind stress curl. New insights derive from an understanding of links with the upper troposphere. As the SIO-RWs move westward with the onset of an El Niño in the Pacific, increased convection over the north Indian Ocean corresponds to reduced evaporation and SST warming. Mid-tropospheric heating T′ > 2°C over the northwest Indian Ocean accelerates the southern sub-tropical jet to greater than 10 m s −1 over the southeast Indian Ocean, reinforcing the anticyclonic vorticity. The downstream acceleration of the jet generates upper-level divergence and moist convection over the western basin, anchoring an atmospheric Rossby wave in a northwest–southeast alignment underpinned by differential propagation of the SIO-RW. As the ocean Rossby wave reaches Africa, the coupling fades and transitions. What distinguishes Indian Ocean from Pacific Ocean Rossby waves are their southern latitude and higher frequency. The tropical mid-tropospheric heating that accelerates the southern sub-tropical jet shifts westward in tandem with the SIO-RW.