Assessing Spatial Patterns and Trends in the Sea Level Annual Cycle

Changes in the sea level annual cycle, a dominant contributor to sea level variability across timescales, can impact coastal flood risks. Previous investigation into the patterns, drivers, and long-term changing nature of the sea level annual cycle has been largely observation based and has been thus limited in spatio-temporal resolution. Here, we use NOAA GFDL’s CM4 Global Climate Model, a coupled ocean-atmosphere model, to investigate patterns and changes in the sea level annual cycle throughout the 20th and 21st centuries. We use harmonic analyses to calculate time mean and time varying annual amplitude and phase to enable comparison to equivalent observational estimates and to investigate variability over time. Results largely agree with previous observational studies, such as in the Gulf Stream which shows large changes in amplitudes over the period. Continued research will relate patterns of change to internal modes of climate variability as well as the effects of anthropogenically driven ocean heat uptake, and will determine the drivers of sea level annual amplitude and phase changes. Continued work will help us better understand climate variability manifesting in the sea level seasonal cycle and lead to improved predictions of sea level change, particularly at the coast.