Aquarius is a combined passive/active L-band microwave instrument that is being developed to map the salinity field at the surface of the ocean from space. The data will support studies of the coupling between ocean circulation, global water cycle, and climate. Aquarius is part of the Aquarius/Satelite de Aplicaciones Cientiflcas-D mission, which is a partnership between the U.S. (National Aeronautics and Space Administration) and Argentina (Comision Nacional de Actividades Espaciales). The primary science objective of this mission is to monitor the seasonal and interannual variation of the large-scale features of the surface salinity field in the open ocean with a spatial resolution of 150 km and a retrieval accuracy of 0.2 psu globally on a monthly basis.
This study delineates the salinity fronts (SF) across the tropical Pacific, and describes their variability and regional dynamical significance using Aquarius satellite observations. From the monthly maps of the SF, we find that the SF in the tropical Pacific are (1) usually observed around the boundaries of the fresh pool under the intertropical convergence zone (ITCZ), (2) stronger in boreal autumn than in other seasons, and (3) usually stronger in the eastern Pacific than in the western Pacific. The relationship between the SF and the precipitation and the surface velocity are also discussed. We further present detailed analysis of the SF in three key tropical Pacific regions. Extending zonally around the ITCZ, where the temperature is nearly homogeneous, we find the strong SF of 1.2 psu from 7° to 11°N to be the main contributor of the horizontal density difference of 0.8 kg/m3. In the eastern Pacific, we observe a southward extension of the SF in the boreal spring that could be driven by both precipitation and horizontal advection. In the western Pacific, the importance of these newly resolved SF associated with the western Pacific warm/fresh pool and El Niño southern oscillations are also discussed in the context of prior literature. The main conclusions of this study are that (a) Aquarius satellite salinity measurements reveal the heretofore unknown proliferation, structure, and variability of surface salinity fronts, and that (b) the fine-scale structures of the SF in the tropical Pacific yield important new information on the regional air-sea interaction and the upper ocean dynamics.
The European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission aims at obtaining global maps of soil moisture and sea surface salinity from space for large-scale and climatic studies. It uses an L-band (1400-1427 MHz) Microwave Interferometric Radiometer by Aperture Synthesis to measure brightness temperature of the earth's surface at horizontal and vertical polarizations (T/sub h/ and T/sub v/). These two parameters will be used together to retrieve the geophysical parameters. The retrieval of salinity is a complex process that requires the knowledge of other environmental information and an accurate processing of the radiometer measurements. Here, we present recent results obtained from several studies and field experiments that were part of the SMOS mission, and highlight the issues still to be solved.
Sea Surface Salinity (SSS) is a key parameter in the global water cycle but it is not yet monitored from space. Conventional in situ SSS sampling is too sparse to give the global view of salinity variability that a remote sensing satellite can provide. The Aquarius/SAC-D Mission will make pioneering space-based measurements of global SSS with the precision, resolution, and coverage needed to characterize salinity variations (spatial and temporal), investigate the linkage between ocean circulation, the Earth's water cycle, and climate variability. It is being jointly developed by NASA and the Space Agency of Argentina, the Comision Nacional de Actividades Espaciales (CONAE). The Project is currently in implementation phase with the flight Aquarius Instrument undergoing environmental testing at NASA-JPL/Caltech in California, USA and the SAC-D instruments and spacecraft development undergoing at CONAE/INVAP facilities in Argentina. Aquarius/SAC-D launch is scheduled for May 2010.
In-situ observing system has provided the capability to monitor multi-decadal changes of salinity in the open ocean and on large scales. However, in-situ platforms are inadequate to monitor salinity changes in marginal seas and coastal oceans as well as salinity variations on mesoscales. Monitoring longer-term changes of salinity in these regions and scales are important to the studies of terrestrial-ocean water cycle linkage, cross-shelf exchanges, coastal-open ocean connection, energy transfer, and biogeochemistry. Satellite measurements of sea surface salinity (SSS) have demonstrated their values to enhance salinity observing capability in these regions and scales. This presentation highlights the accomplishments of satellite SSS, especially in studying salinity variations for regions and scales not well resolved by in-situ platforms. Examples will be provided to emphasize the synergy of satellite and in-situ salinity observing systems to investigate the linkage of open-ocean and marginal sea salinity in relation to longer-term changes in the climate and water cycle. Recognizing this need, the Global Climate Observing System (GCOS) Implementation Needs (Belward et al.2016) suggested Action 032: Ensure the continuity of space-based SSS measurements. Sustaining satellite SSS observing capability, enhancing spatial resolution, and improving accuracy (especially in high-latitude oceans) are important to studying the linkages of the ocean with the water cycle and climate variability.
