Global Climatology and Trends of the Dominant Wave Breaking Probability

Abstract

Wave breaking is the dominant physical process responsible for energy dissipation of ocean surface waves and is critical for exchanges of momentum, energy and mass across the air-sea interface. Over the past two decades, extensive research efforts have been devoted to investigating the climatology and trends of wind speed and wave height in global oceans, revealing their upward trends over the past several decades. Nonetheless, research on global-scale wave breaking statistics remains relatively limited. It is not immediately clear whether wave steepness and wave breaking have intensified because the trends of wavelength are unknown. In this paper, we first present a simplified theoretical analysis based on the empirical wind-sea fetch laws and Toba’s 3/2 power law. A climatological relation between wind-sea wave steepness and wind speed is obtained, which suggests that as a consequence of accelerating winds on a climatological timescale, wave height grows faster than wavelength does and thus results in amplified steepness and intensified wave breaking. We then conduct a thorough analysis of global climatology and trends of the dominant wave breaking probability b T , an important proxy of wave breaking estimated empirically from a recently produced global wave hindcast over the period from 1992 to 2019. It is confirmed that in the Southern Ocean (global oceans), b T has increased by approximately 4% (2%) over the past 28 years, and these relative trends of b T are comparable to those for wind speed and wave height.