Surface Wave Climatology

Overview

In 2017, I began working with Dr. Sarah T. Gille on a project investigating the intra-annual variability of significant wave height (SWH) in regards to SWH relationship with local wind speed (WSP). The sinusoidal annual cycle of SWH, generated by large-scale seasonal patterns in storms, is the dominant signal for the majority of the world’s oceans. However, we observed important deviations from the annual cycle due to local wind events. Off the coast of California, a particular deviation, identified as having an increase in SWH during early summer, occurs due to expansion fan wind events. WSP reaches a maximum during early summer giving SWH and WSP a characteristic annual cycle phase difference of nearly 90 degrees. In other hypothesized expansion fan wind regions known as summer wind anomaly regions (SWARs), deviations from the SWH annual cycle are largely unexplored and the impact of these wind events on the wave field’s sea state is unclear. Using regional climatologies of SWH and WSP, the magnitude of the deviation from the SWH annual cycle in SWARs is shown to be determined by the local conditions and characteristics of the wave field (e.g. extent SWARs are sheltered from regions with storms that produce remotely forced waves). These deviations imply that the wave field is dominated by locally forced waves during the anomalous wind events while for the remainder of the time, the wave field is primarily dominated by remotely forced waves. Modulation of the wave field by strong wind events may lead to enhanced wave breaking which could have implications for air-sea fluxes.

Figure 1: SWH (solid blue curve) and WSP (solid red curve) climatologies in 4 degree by 4 degree region within SWAR located off the California Coast. Shading represents the standard error of the mean and dotted blue and red lines are the annual plus semi-annual cycle least-squares fitted to monthly climatology for SWH and WSP respectively.