Sea surface salinity under rain cells: SMOS satellite and in situ drifters observations

Abstract

We study the signature of rainfall on S 1cm , the sea surface salinity retrieved from the Soil Moisture and Ocean Salinity (SMOS) satellite mission first by comparing SMOS S 1cm with ARGO sea surface salinity measured at about 5 m depth in the Intertropical Convergence Zone (ITCZ) and in the Southern Pacific Convergence Zone; second by investigating spatial variability of SMOS S 1cm related to rainfall. The resulting estimated S 1cm decrease associated with rainfall occurring within less than 1 h from the salinity measurement is close to 20.2 pss (mm h 21 ) 21. We estimate that rain induced roughness and atmospheric effects are responsible for no more than 20% of this value. We also study the signature of rainfall on sea surface salinity measured by surface drifters at 45 cm depth and find a decrease associated with rainfall of 20.21 (60.14) pss (mm h 21 ) 21, consistent with SMOS observations. When averaged over one month, this rain associated salinity decrease is at most 20.2 in monthly 100 3 100 km 2 pixels, and at most 40% of the difference between SMOS S 1cm and interpolated in situ bulk salinity in pixels near the ITCZ. This suggests that more than half of this difference is related to the in situ products obtained from optimal interpolation and therefore influenced by smoothing and relaxation to climatology. Finally, further studies on the satellite-derived salinities should pay attention to that as well as to other sources of uncertainties in satellite measurements and not interpret fully the observed differences between in situ and satellite mapped products, as rain induced SSS variability.

Evaluation of Drifter Salinities in the Subtropical North Atlantic

“…Recently, salinity measurements from drifters have been shown to capture well the effect of precipitation on the ocean (e.g., Reverdin et al 2012;Boutin et al 2014). To verify if large drops in the observed salinitiesparticularly when not confirmed by Argo/Aquarius data or nearby drifters-may be related to rain events, we attempted to compare such freshwater spikes with TRMM 3B42 precipitation rates mapped onto the individual SVP-S tracks using a method similar to the Aquarius SSS retrievals.…”

Multi-dimensional interpolation of SMOS sea surface salinity with surface temperature and in situ salinity data

“…These data, however, are quite noisy due to both intrinsic instrumental issues and complex retrieval algorithms, and thus present large scale errors (evidenced by ascending/descending pass differences) and small scale errors/contamination by atmospheric effects (e.g. Martin-Neira et al, 2013;Yin et al, 2013;Boutin et al, 2014). Moreover, the low sensitivity of L-band brightness temperature to salinity at low temperatures and the impact of wind speed on the retrieval represent a further limitation at the high latitudes.…”

“…In fact, SMOS data are known to be affected by both large scale errors and small scale noise or signals related to processes other than 'bulk' surface salinity variations (e.g. Martin-Neira et al, 2013;Yin et al, 2013;Boutin et al, 2014). Some of these errors are immediately identified even through a simple visual inspection of single L3 images (see example in the upper panel of Fig.…”

“…Moreover, several specific accuracy issues affecting satellite products still need specific investigations (e.g. high latitude ascending/descending orbits large scale differences, high latitude large scale bias with respect to in situ L4 data, or local response to intense rain cells, see also Boutin et al, 2014;Yin et al, 2013;Font et al, 2013).…”

The Spatial and Temporal Variability of Air-Sea CO2 Fluxes and the Effect of Net Coral Reef Calcification in the Indonesian Seas: A Numerical Sensitivity Study

“…For SSS comparison, SMOS (soil moisture and ocean salinity sensor) derived data represent-with an accuracy of 0.4 psuthe upper ≈ 1 cm of the ocean surface (Boutin et al, 2014). time series are presented in panels 1-7 of Figure 4.…”