A new JEDI-based global sea level product at ¼ degree resolution

Sea level is a high impact essential variable for a wide range of applications ranging from coastal engineering and storm surge to tidal prediction, fisheries, climate variability and change. Yet, despite its wide range of applications there are very few data-driven global sea level products that are available at a quasi-operational timescale. Here we report on development of a new daily ¼-deg global sea level product, JEDI/RADS sea level, being developed as an improved product for NOAA Coastwatch.

The first part of the talk reviews construction of JEDI/RADS sea level. The primary data sets are along-track {1 sec} sea level observations from 13 altimeter satellites that were archived in the Radar Altimeter Database System (RADS) along with the necessary corrections for atmospheric path delay, ocean tides, and other geophysical effects. Long wavelength systematic differences among the individual satellite records are minimized by a preconditioning long wavelength adjustment to a set of reference missions. Objective mapping is then carried out using the JEDI 3DVar modified to account for the well-documented zonal propagation of eddies, as well as for the presence of long-wavelength coastal waves (which reduce alongshore pressure gradients). Mean dynamic topography is provided by the new 1993-2012 Mean Dynamic Topography MDT-CNES-CLS2022. The potential for further improvement made possible with a 4DVar filter will be discussed.

The second half of the talk examines systematic and random error based on comparison to the widely used Copernicus Marine Environment Monitoring Service Ssalto/Duacs multimission daily global altimeter sea level product and to a reference set of coastal and island tide gauges. Geostrophic surface current estimates are compared to the new Coastwatch Blended Ocean Surface Currents (BOSC) as well as to Global Drifter Program drifter trajectories. The talk then examines the time evolution of sea level during 2000-2022 beginning with global sea level. As shown in Fig. 1 global sea level contains 1) thermal expansion-related seasonal changes, 2) a nearly constant decadal rate of sea level rise, and 3) ENSO-related year to year anomalies (e.g. 2011 and 2016).