Changing Atmospheric Drivers of Future Sea Level Variability

Along with global sea level rise contributions from thermal expansion and meltwater, changes in high-frequency sea level anomalies compound increasing risks to coastal communities. The high-frequency events are closely linked to weather-scale phenomena and atmospheric forcing. Here we consider the variability of dynamic sea level (DSL) and the inferred inverse barometer height (IBH) contributions from atmospheric pressure variability and assess how this variability might change in a warmer climate. Using a hierarchy of global climate models (GFDL-CM4X; Griffies et al. in prep.) with varying atmospheric (100km, 50km) and ocean (0.25-degree, 0.125-degree) horizontal grid spacing, we explore both the trends and changes in variability under a high emissions climate warming scenario (SSP5-8.5). We find that future IBH trends are an order of magnitude less than the DSL trends, yet the IBH trends are negative across much of the low and middle latitudes and offset positive trends in DSL. The detrended, de-seasoned daily variance in combined (IBH+DSL) sea level is projected to increase throughout most of the global ocean, especially in the deep mixed layer regions of the Southern Ocean, western boundary currents, and shallow shelf regions of the Arctic Ocean. The combined sea level variance is projected to decrease, however, in the North Atlantic basin and there is a weakening and southward shift in the Gulf Stream that is more pronounced in the higher-resolution ocean model. Projected changes in the IBH variance are generally smaller compared with DSL, but there is an atmospheric resolution dependence leading to more IBH variability over the Southern Ocean. At US tide gauge locations, the fractional contribution of the IBH to the combined variance is projected to decrease along the US West Coast and increase along the US East Coast. Along the West Coast, increasing ocean resolution and a poleward shift in the midlatitude storm track may be contributing to decreased IBH contributions to variability while along the US East Coast, reduced Gulf Stream variability could be linked to the reduced contributions from dynamic sea level. This work demonstrates how differing model grid spacing on the atmosphere and ocean may contribute to projections of future sea level variability and will help interpret predictions and projections of sea level extremes.