On the role of extratropical air‐sea interaction in the persistence of the Southern Annular Mode

• Published in: Geophysical research letters 2016-08, Vol.43 (16), p.8806-8814
• Main Authors: Xiao, Bei, Zhang, Yang, Yang, Xiu‐Qun, Nie, Yu
• Format: Article
• Language: English
• Subjects: Annular; Anomalies; Eddies; eddy‐mean flow interaction; extratropical air‐sea interaction; Geophysics; Latitude; Marine; Meteorology; Ocean-atmosphere interaction; Oceans; Sea surface temperature; Southern Annular Mode; Spectral analysis; Time
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL070255

Using the daily atmosphere and ocean reanalysis data, this study highlights the role of extratropical air‐sea interaction in the variability of the Southern Annular Mode (SAM). Our analysis shows that the SAM‐induced meridional dipolar sea surface temperature (SST) anomalies, through surface heat fluxes, can maintain persistent lower tropospheric temperature anomalies, which further results in anomalous eddy momentum forcing enhancing the persistence of the SAM. With the Finite Amplitude Wave Activity diagnosis, we illustrate that response of the eddy momentum forcing to SST anomalies can be attributed to changes in both baroclinic processes as baroclinic eddy generation and barotropic processes as wave breaking thus resultant diffusive eddy mixing, with the former confined at high latitudes and the latter strongest at midlatitudes. Spectral analysis further suggests that the above air‐sea interactions are important for bimonthly and longer time scale SAM variations. The dipolar SST pattern may be an indicator for predicting subseasonal and interseasonal variabilities of the SAM. Key Points Daily reanalysis data show evidence that air‐sea interactions enhance the persistence of SAM Ocean feeds back to SAM via both barotropic mechanism at midlatitude and baroclinic mechanism at high latitude Air‐sea interactions are suggested to be important for the bimonthly and longer time scale variabilities of the SAM