ALBERT

Beschreibung: Space-time variability of SSS in the Atlantic Ocean (33°S-80°N) is analyzed using near surface salinity observations from the period 1980-2013 jointly with the output from an eddy-resolving numerical ocean simulation. Results show a good agreement between in situ and model results in terms of spatial and temporal mean SSS patterns, geographically-varying SSS variability, and spatial and temporal scales of SSS variability. A good agreement exists also for estimates of the amplitude and phase of the annual cycle of SSS with the model providing more spatial details of SSS variability, which cannot be resolved by observations, especially near ocean margins and in shelf areas. Dominant spatial and temporal scales of SSS variability are, respectively, between 100 and 250 km and between 30 and 70 days in most of the Atlantic when the annual cycle of the SSS is included. However, smaller-scale salinity features are also present, which show temporal decorrelation scales of only 3-5 days throughout the Atlantic. This fast variability must be considered when producing weekly averaged salinity products from satellite measurements. This article is protected by copyright. All rights reserved.

Beschreibung: Space-borne sea surface salinity (SSS) measurements provided by the European Space Agency's (ESA) “Soil Moisture and Ocean Salinity” (SMOS) and the National Aeronautical Space Agency's (NASA) “Aquarius/SAC-D” missions, covering the period from May 2012 to April 2013, are compared against in situ salinity measurements obtained in the northern North Atlantic between 20° N and 80° N. In cold water, SMOS SSS fields show a temperature-dependent negative SSS bias of up to -2 g/kg for temperatures 〈 5 °C. Removing this bias significantly reduces the differences to independent ship-based thermosalinograph data but potentially corrects simultaneously also other effects not related to temperature, such as land contamination or Radio Frequency Interference (RFI). The resulting time-mean bias, averaged over the study area, amounts to 0.1 g/kg. A respective correction applied previously by the Jet Propulsion Laboratory to the Aquarius data is shown here to have successfully removed an SST-related bias in our study area. For both missions, resulting spatial structures of SSS variability agree very well with those available from an eddy-resolving numerical simulation and from Argo data and, additionally they also show substantial salinity changes on monthly and seasonal time scales. Some fraction of the root-mean-square difference between in situ, and SMOS and Aquarius data (approximately 0.9 g/kg) can be attributed to short-time scale ocean processes, notably at the Greenland shelf, and could represent associated sampling errors there. This article is protected by copyright. All rights reserved.