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Global wave number-4 pattern in the southern subtropical sea surface temperature
Balaji Senapati1, Mihir K Dash2, Swadhin K Behera3
1Centre for Oceans, Rivers, Atmosphere and Land Sciences, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India.
Scientific Reports
|January 9, 2021
Summary
A stationary wavenumber-4 pattern in sea surface temperature anomalies (W4) influences Australian rainfall by altering atmospheric circulation. This W4 pattern is seasonally locked to austral summer and independent of other climate variabilities.
Area of Science:
- Oceanography
- Atmospheric Science
- Climate Dynamics
Background:
- A stationary zonal wavenumber-4 (W4) pattern in sea surface temperature (SST) anomalies has been identified in the southern subtropics (20°S-55°S).
- This W4 pattern is seasonally phase-locked to the austral summer and can persist until mid-autumn.
Purpose of the Study:
- To investigate the generation and termination mechanisms of the W4 pattern.
- To understand the influence of the W4 pattern on Australian rainfall through modulation of local atmospheric circulation.
Main Methods:
- Empirical Orthogonal Function (EOF) analysis was employed to identify the W4 pattern.
- Thermodynamic coupling between the atmosphere and upper ocean was examined as a generation mechanism.
- Correlation analysis was used to assess the independence of the W4 pattern from other climate variabilities like ENSO, SAM, and IOD.
Main Results:
- The W4 pattern is generated by atmosphere-ocean thermodynamic coupling and terminates due to feedback breaking.
- Positive W4 events correlate with cold SST anomalies around Australia, leading to anomalous divergence and increased rainfall in southeastern Australia.
- Negative W4 events show reversed effects, and an observed asymmetry in W4 peak occurrence may explain weaker SST signals south of Australia.
Conclusions:
- The W4 SST anomaly pattern significantly impacts Australian rainfall by influencing atmospheric circulation.
- The W4 pattern is largely independent of major climate variabilities, suggesting it represents a distinct mode of climate variability.
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