Evidence of organized intraseasonal convection linked to ocean dynamics in the Seychelles–Chagos thermocline ridge
The Madden–Julian oscillation (MJO) is the dominant driver of intraseasonal variability across the equatorial domain of the global ocean with alternating wet and dry bands that propagate eastward primarily between 5°N and 5°S. Past research has shown that MJOs impact the surface and subsurface variability of the Seychelles–Chagos thermocline ridge (SCTR) (55°E–65°E, 5°S–12°S) located in the southwest tropical Indian Ocean (SWTIO), but investigations of how SWTIO internal dynamics may play an important role in producing MJO events remain limited. This study uses Argo, in conjunction with several remote sensing and reanalysis products, to demonstrate that SWTIO oceanic dynamics, particularly barrier layer formation and near surface heat buildup, may be associated with MJO genesis between August and December of most years between 2005 and 2013. A total of eight SWTIO specific MJO events are observed, all occurring between August and December. Four of the eight events are correlated with positive SWTIO total heat content (THC) and barrier layer thickness (BLT) interannual anomalies. Two others formed over the SWTIO during times when only one of the variables was at or above their seasonal average, while two additional events occurred when both variables experienced negative interannual anomalies. Lacking complete 1:1 correlation between the hypothesized oceanic state and the identified SWTIO MJO events, we conclude that additional work is required to better understand when variability in key oceanic variables plays a primary role in regional MJO genesis or when other factors, such as atmospheric variability, are the dominate drivers.
KeywordsSeychelles–Chagos thermocline ridge MJO SWTIO BLT
This work is supported by the Office of Naval Research (ONR) Award #N00014-15-1-2591 awarded to BS. JMD is supported by the Naval Research Laboratory Cooperative Agreement BAA-N00173-03-73-13-01 awarded to The University of Southern Mississippi. NOAA interpolated outgoing longwave radiation (OLR) data were obtained from http://www.esrl.noaa.gov/psd/data/gridded/data.interp_OLR.html. Argo temperature and salinity data were obtained from the Asia Pacific Data-Research Center (APDRC) (http://apdrc.soest.hawaii.edu/projects/argo/). Merged TRMM data were obtained from NASA Goddard Space Flight Center (http://trmm.gsfc.nasa.gov/data_dir/data.html). ECMWF ERA-Interim data used in this study/project have been provided by ECMWF/have been obtained from the ECMWF data server http://apps.ecmwf.int/datasets/data/interim-full-daily/. The authors would like to thank the anonymous reviewers and the editor whose comments significantly contributed to the improvement of this paper.
- Chowdary JS, Gnanaseelan C (2007) Basin-wide warming of the Indian Ocean during ElGoogle Scholar
- Dijkstra HA (2008) Dynamical oceanography. Springer, Berlin, p 276Google Scholar
- Liebmann B, Smith CA (1996) Description of a complete (interpolated) outgoing longwave radiation dataset. Bull Am Meteorol Soc 77:1275–1277Google Scholar
- Niño and Indian Ocean dipole years. Int J Climatol 27:1421–1438. https://doi.org/10.1002/joc.1482
- Takayabu YN, Iguchi T, Kachi M et al (1999) Abrupt termination of the 1997–1998 El Niño in response to a Madden–Julian Oscillation. Nature 402: 279–282. https://doi.org/10.1038/46254