Intraseasonal Variability of Surface Salinity in the Eastern Tropical Pacific Associated With Mesoscale Eddies

Abstract

Strong variability in sea surface salinity (SSS) in the Eastern Tropical Pacific (ETPac) on intraseasonal to interannual timescales was studied using data from the Soil Moisture and Ocean Salinity, Soil Moisture Active Passive, and Aquarius satellite missions. A zonal wave number‐frequency spectral analysis of SSS reveals a dominant timescale of 50–180 days and spatial scale of 8°–20° of longitude with a distinct seasonal cycle and interannual variability. This intraseasonal SSS signal is detailed in the study of 19 individual ETPac eddies over 2010–2016 identified by their sea level anomalies, propagating westward at a speed of about 17 cm/s. ETPac eddies trap and advect water in their core westward up to 40° of longitude away from the coast. The SSS signatures of these eddies, with an average anomaly of 0.5‐pss magnitude difference from ambient values, enable the study of their dynamics and the mixing of their core waters with the surroundings. Three categories of eddies were identified according to the location where they were first tracked: (1) in the Gulf of Tehuantepec, (2) in the Gulf of Papagayo, and (3) in the open ocean near 100°W–12°N. They all traveled westward near 10°N latitude. Category 3 is of particular interest, as eddies seeded in the Gulf of Tehuantepec grew substantially in the vicinity of the Clipperton Fracture Zone rise and in a region where the mean zonal currents have anticyclonic shear. The evolution of the SSS signature associated with the eddies indicates the importance of mixing to their dissipation.

On the Factors Driving Upper-Ocean Salinity Variability at the Western Edge of the Eastern Pacific Fresh Pool

“…The theoretical meridional Ekman current is a reasonably good match to the observed layer-averaged meridional current during the trade wind season of January–May ( Figure 6 , lower panel). During the January–June period, the fluctuations of the observed meridional velocity around the theoretical Ekman current at periods of one to two months are likely associated with the intraseasonal eddies that are prevalent in this region ( Farrar and Weller, 2006 ; Hasson et al, in press ). The agreement of the theoretical northward Ekman current and the observed meridional velocity is notably worse during September–November 2016 and from September 2017 to the end of the record—it is not clear why this happens, but the explanation could involve intraseasonal eddies or some other dynamics associated with the NEC/NECC current system.…”

“…The westward-flowing North Equatorial Current (NEC) and eastward-flowing North Equatorial Counter Current (NECC) are also potentially major influences. The 10°N site is in between the climatological average locations of the NECC (5°–8°N) and NEC (10°–15°N), but the two currents move north and south and vary in intensity seasonally with the ITCZ and trade winds (e.g., Farrar and Weller, 2006 ; Hasson et al, in press ).…”

Modulation of Shelf Circulations Under Multiple River Discharges in the East China Sea

“…The increased spatial coverage provides opportunities for applying SMAP data for high resolution studies. SMAP now is widely used in ocean (Hasson et al, 2019;Vazquez-Cuervo et al, 2019) and river plume (Brokaw et al, 2019;Kida et al, 2019;Mathur et al, 2019) studies, although there are uncertainties in coastal regions. Standard deviation errors near the coasts are 10 times larger than those on oceans (Martin et al, 2019).…”

Satellite‐Based Sea Surface Salinity Designed for Ocean and Climate Studies

“…As this study started, individual satellite SSS is capable of resolving the upper register of the mesoscale spectrum (spatial scale of 50–500 km and temporal scale of 10–100 days) (e.g., Hasson et al., 2019; Huang et al., 2021; Kolodziejczyk et al., 2021; Lin et al., 2019; Melnichenko et al., 2021; Olivier et al., 2020). These scales play an important role in the mixing and exchanges of water masses close to fronts, as a result of ocean circulation and atmospheric fluxes.…”