Influence of Natural Climate Variability on the Extreme Ocean Surface Wave Heights Over the Indian Ocean

Abstract

Extreme ocean waves are part of the climate system but responsible for significant impacts on coastal and offshore environments, structures, and populations. In the Indian Ocean (IO), the wind and wave climate can be significantly influenced by natural climate variability, such as the El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Southern Annular Mode (SAM), yet our understanding on their regional influence is limited, particularly for seasonal extremes. Here, seasonal extreme significant wave heights (SWHs) and winds in the IO are examined over the period 1957–2010 utilizing ERA‐20C reanalysis data and the nonstationary generalized extreme value distribution to understand climatic extremes, by considering climate indices as covariates. ENSO influence on extreme SWHs include increases in the Bay of Bengal, southwest tropical IO (TIO), southern IO (SIO; a broad extension south of Australia), and South China and Philippine (SCP) Seas, and decreases in the Arabian Sea in boreal summer during El Niño. Extreme SWH responses to the IOD include increases in the eastern TIO, southwest TIO, and SIO in boreal autumn during its positive phase. Lastly, Southern Annular Mode not only significantly affects the SIO year round but has a weak influence in the northern and tropical IO. Composite analysis of ENSO and IOD events further highlight in phase combinations display less significant influence than out of phase combinations during summer, but not autumn. Mean and extreme wind responses are consistent with SWH responses to natural climate variability, and climate mode teleconnection patterns help explain the seasonal variations.

Climate Variability Impacts on Global Extreme Wave Heights: Seasonal Assessment Using Satellite Data and ERA5 Reanalysis

“…In this respect, when examining SAM influence on wave height extremes after removing ENSO based on a linear regression, there is no prominent differences in Hmax responses (figure not shown), which is also reported by Kumar et al. (2019) for Indian Ocean. A. G. Marshall et al.…”

“…Using the same method and ERA‐20C reanalysis, Kumar et al. (2019) examined seasonally distinct responses of extreme SWHs over the Indian Ocean to ENSO, SAM, and the Indian Ocean Dipole (IOD), finding the same physical mechanism at work.…”

“…They focused on Northern Hemisphere variability in extreme SWH, and further examined its connection with variability in wind speed and sea-level pressure (SLP) gradient amplitude to highlight that atmospheric teleconnection pattern induces the extreme SWH changes. Using the same method and ERA-20C reanalysis, Kumar et al (2019) examined seasonally distinct responses of extreme SWHs over the Indian Ocean to ENSO, SAM, and the Indian Ocean Dipole (IOD), finding the same physical mechanism at work. The current study aims at investigating the impacts of the major modes of interannual climate variability on seasonal extreme SWH, using merged satellite altimeter datasets and ERA5 reanalysis for an extended period spanning 1992-2016.…”

Influence of Natural Climate Variability on Extreme Wave Power over Indo-Pacific Ocean Assessed using ERA5

“…0.312, p-value<0.05) and SON (0.620, p-value<0.01). The significant correlation between ENSO and IOD in JJA and SON suggests that IOD can be largely determined by ENSO and seasonally modulated responses, yet some IOD events can occur independently of ENSO events (Cai et al 2011;Kumar et al 2019;Stucker et al 2017). When analyzing the independent impact of each climate variability mode, the dependency of one climate variability index on the other is removed using linear regression analysis.…”

“…In MAM, ENSO reduces the PDO signals over the PO. In addition, seasonal SLP teleconnection patterns regressed against ENSO|IOD, IOD|ENSO, ENSO|IOD, and PDO|ENSO, exhibit a high and low pressure anomaly that in turn generates strong winds(Kumar et al 2016(Kumar et al , 2019Patra et al 2020;Remya et al, 2020;Yang and Oh 2018) and consequently enhances the wave parameters (i.e. Hs and Tp) in the respective localized regions.…”