Accounting for the Nodal Tide to Improve Estimates of Sea Level Acceleration

The 18.6-year nodal tide is a component of all tide gauge records. It can affect estimates of sea level acceleration, in particular for tide gauge records with lengths of less than 60 years. We provide an analytic solution that shows the effect of the nodal tide on estimates of sea level trend and acceleration. By adding a term to the least squares formulation used to estimate sea level trend and acceleration, we can account for the nodal tide and eliminate its effect on the estimate. Using representative world-wide tide gauge records, we demonstrate that accounting for the nodal tide can improve estimates, particularly of acceleration.