Search for Trends and Periodicities in Inter-hemispheric Sea Surface Temperature Difference

• Published in: Pure and applied geophysics Vol. 175; no. 6; pp. 2381 - 2394
• Main Authors: Rajesh, R., Tiwari, R. K.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.06.2018; Springer Nature B.V
• Subjects: Amplitude modulation; Atmospheric models; Atmospheric processes; Carbon dioxide; Climate; Climate change; Climate models; Climate variability; Climatic analysis; Components; Data; Dynamics; Earth and Environmental Science; Earth Sciences; El Nino; Frequencies; Geophysics/Geodesy; Irradiance; Modelling; Ocean dynamics; Ocean models; Ocean temperature; Oceans; Oscillations; Periodicities; Sea surface; Sea surface temperature; Solar activity; Solar cycle; Solar irradiance; Solar periodicities; Solar variability; Spectral analysis; Statistical analysis; Statistical methods; Surface chemistry; Surface temperature; Temperature; Temperature differences; Thermal cycling; Trends; Variability; Variance; Variance analysis; ocean–atmospheric circulations; solar forcing; SST; trend; modulations
• ISSN: 0033-4553; 1420-9136
• DOI: 10.1007/s00024-018-1791-3

Understanding the role of coupled solar and internal ocean dynamics on hemispheric climate variability is critical to climate modelling. We have analysed here 165 year long annual northern hemispheric (NH) and southern hemispheric (SH) sea surface temperature (SST) data employing spectral and statistical techniques to identify the imprints of solar and ocean–atmospheric processes, if any. We reconstructed the eigen modes of NH-SST and SH-SST to reveal non-linear oscillations superimposed on the monotonic trend. Our analysis reveals that the first eigen mode of NH-SST and SH-SST representing long-term trend of SST variability accounts for ~ 15–23% variance. Interestingly, these components are matching with first eigen mode (99% variance) of the total solar irradiance (TSI) suggesting possible impact of solar activity on long-term SST variation. Furthermore, spectral analysis of SSA reconstructed signal revealed statistically significant periodicities of ~ 63 ± 5, 22 ± 2, 10 ± 1, 7.6, 6.3, 5.2, 4.7, and 4.2 years in both NH-SST and SH-SST data. The major harmonics centred at ~ 63 ± 5, 22 ± 2, and 10 ± 1 years are similar to solar periodicities and hence may represent solar forcing, while the components peaking at around 7.6, 6.3, 5.2, 4.7, and 4.2 years apparently falls in the frequency bands of El-Nino-Southern Oscillations linked to the oceanic internal processes. Our analyses also suggest evidence for the amplitude modulation of ~ 9–11 and ~ 21–22 year solar cycles, respectively, by 104 and 163 years in northern and southern hemispheric SST data. The absence of the above periodic oscillations in CO 2 fails to suggest its role on observed inter-hemispheric SST difference. The cross-plot analysis also revealed strong influence of solar activity on linear trend of NH- and SH-SST in addition to small contribution from CO 2 . Our study concludes that (1) the long-term trends in northern and southern hemispheric SST variability show considerable synchronicity with cyclic warming and cooling phases and (2) the difference in cyclic forcing and non-linear modulations stemming from solar variability as a possible source of hemispheric SST differences.