Coastal sea level trends over 2002-2018 from reprocessed Jason-1, 2, 3 satellite altimetry

Abstract:

We present a 16-year-long (June 2002 to May 2018), high-resolution (~300 m), along-track sea level dataset at monthly interval, together with associated sea level trends, at 429 coastal sites in six regions (Northeast Atlantic, Mediterranean Sea, West Africa, North Indian Ocean, Southeast Asia and Australia). This new coastal sea level product is based on complete reprocessing of raw radar altimetry waveforms from the Jason-1, Jason-2 and Jason-3 missions. Unlike classical altimetry, it provides valid sea level data very close to the coast, at distances <3-4 km from the coastline in general, sometimes even closer, within 1-2 km from the coast. The coastal sea level trends, computed over 2002-2018, show no significant difference (within +/-1 mm/yr) with open ocean trends for 80% of the studied sites. Although it had been expected that coastal processes may cause discrepancy in coastal sea level trends compared to the open ocean, these new results seem to contradict this hypothesis. An important consequence of this observation is that it would be possible to extrapolate regional sea level trends computed by classical altimetry missions, up to the coast. However, this is not true everywhere. Indeed, at a few sites, we observe a larger sea level trend close to the coast than offshore, while in some other cases, we note a decrease in trend as the distance to the coast decreases. Small-scale coastal processes able to explain such different trend behaviors close to the coast are investigated.