Multi-temporal variation of the Ross Sea Polynya in response to climate forcings

ABSTRACT

The multi-temporal scales of two physical characteristics (areas and occurrence time) of the Ross Sea Polynya (RSP) in Antarctica were analysed using a sea-ice concentration data set (1979–2014) derived from the Scanning Multichannel Microwave Radiometer, the Special Sensor Microwave Imager and Sensor Microwave Imager Sounder. Then, the Ensemble Empirical Mode Decomposition (EEMD) was applied to the data sets to decompose signals into finite numbers of intrinsic mode functions and a residual mode: long time trend. This approach allowed us to understand the long-term variability of the RSP area and occurrence in response to atmospheric forcing through teleconnections between low and high latitudes by comparing the Nino3.4 and Southern Annular Mode (SAM) indices. The nonlinear trend of the RSP areas derived from the EEMD residual had an upward trending shift in the early 1990s and was fairly consistent with the nonlinear trend of Nino3.4. However, the trend of RSP occurrence time progressively increased and had a significant effect on the long time scale. The trend of the RSP area is significantly correlated (+0.98) with the ratio of the trend of the meridional to zonal wind components related with the nonlinearity of Nino3.4, suggesting that meridional wind stress dominated the changes of the polynya area in the Ross Sea. In addition, the nonlinear trends between the SAM and RSP occurrence time show a strong positive correlation, contributing to the earlier onset of polynya expansion and delayed connection with the open ocean owing to enhanced southerly winds.

KEYWORDS:

• Ensemble Empirical Mode Decomposition (EEMD)
• nonlinear trend
• Southern Ocean
• sea ice
• Antarctica

ABBREVIATIONS:

• EEMD: Ensemble Empirical Mode Decomposition
• ENSO: El Niño–Southern Oscillation
• IMF: intrinsic mode function
• NASA: National Aeronautics and Space Administration
• NCAR: National Center for Atmospheric Research
• NCEP: National Centers for Environmental Prediction
• NSIDC: US National Snow and Ice Data Center
• RMSE: root mean square error
• RSP: Ross Sea Polynya
• SAM: Southern Annular Mode
• SMMR: Scanning Multichannel Microwave Radiometer
• SSM/I: Special Sensor Microwave Imager
• SSMIS: Sensor Microwave Imager Sounder

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This study was carried out with the support of the Satellite Remote Sensing on West Antarctic Ocean Research (STAR) project (no. PE14040) and was a part of the project entitled Ecosystem Structure and Function of Marine Protected Area (MPA) in Antarctica (PM17060) funded by the Ministry of Oceans and Fisheries, Korea.