Improved BEC SMOS Arctic Sea Surface Salinity product v3.1

Abstract

Abstract. Measuring salinity from space is challenging since the sensitivity of the brightness temperature (TB) to sea surface salinity (SSS) is low (about 0.5 K psu−1), while the SSS range in the open ocean is narrow (about 5 psu, if river discharge areas are not considered). This translates into a high accuracy requirement of the radiometer (about 2–3 K). Moreover, the sensitivity of the TB to SSS at cold waters is even lower (0.3 K psu−1), making the retrieval of the SSS in the cold waters even more challenging. Due to this limitation, the ESA launched a specific initiative in 2019, the Arctic+Salinity project (AO/1-9158/18/I-BG), to produce an enhanced Arctic SSS product with better quality and resolution than the available products. This paper presents the methodologies used to produce the new enhanced Arctic SMOS SSS product (Martínez et al., 2019) . The product consists of 9 d averaged maps in an EASE 2.0 grid of 25 km. The product is freely distributed from the Barcelona Expert Center (BEC, http://bec.icm.csic.es/, last access: 25 January 2022) with the DOI number https://doi.org/10.20350/digitalCSIC/12620 (Martínez et al., 2019). The major change in this new product is its improvement of the effective spatial resolution that permits better monitoring of the mesoscale structures (larger than 50 km), which benefits the river discharge monitoring.

Can the Surface Quasi‐Geostrophic (SQG) Theory Explain Upper Ocean Dynamics in the South Atlantic?

“…Salinity observations from remote sensing strongly rely on in situ data for calibration and quality control, and although great improvement was attained since the implementation of SSS observation networks, such as the Voluntary Observing Ships from the French SSS Observation Service (Alory et al., 2015), global coverage is far from being achieved. Therefore the community urges for better salinity observations, especially in high latitudes (Martínez et al., 2021; Vinogradova et al., 2019).…”

Assimilation of sea surface salinities from SMOS in an Arctic coupled ocean and sea ice reanalysis

“…Exp0 assimilated all available altimeter data, SST, sea ice concentration, sea ice drift, T/S profiles, sea ice thickness, except any SMOS SSS products. ExpV2 and ExpV3 additionally assimilated V2.0 and V3.1 of SSS products from BEC, which were tested and retrieved by a series of algorithms considering the low temperature and sea ice cover in the Arctic (Olmedo et al, 2017;Martínez et al, 2022).…”

“…Using the quantitative SSS misfits (Table 2), the impact indexes at each subregion (S1 to S6) further indicates whether the misfits are significantly decreased or not. Outside of the central Arctic, the v2.0 SSS product loses the impacts in this system, but the V3.1 SSS brings more wider significant impacts around the Arctic, which clearly benefits from the related retrieval algorithms for the refined effective resolution (Martínez et al, 2022). However, in the region S6, the SSS in ExpV3 has no significant constraint on the misfits and only brings a reduction in the bias.…”

“…Two strong positive SSS increment centers appear around the Kara Sea and the north of LS, which is clearly different from the increment pattern in ExpV2. The difference is likely due to the processing of the two versions of the SSS products using different climatologies (Martínez et al, 2022). The two nearby regions (BS coast and HB) with negative SSS increment regions in ExpV2 are found to form a dipole of negative and positive increment regions in ExpV3.…”

“…Recently, under the framework of the ESA project Arctic+Salinity and further developing the non-Bayesian scheme, the effective resolutions were enhanced both in space and time. The new version of SSS product (V3.1) shows advantages for monitoring the mesoscale structures and the river discharges (e.g., Martínez et al, 2022), and was released through the BEC portal (also at doi: 10.20350/digitalCSIC/12620; last accessed May 2022). It also provides daily maps of 9-days averages in the Arctic on the regular 25 km grid and covers a longer time-period 2011-2019.…”