Summer in Europe means time for the beach. Testing the waters is a traditional holiday ritual: a swift hand or foot in the surf to check sea temperature. Or there is the modern approach – a flotilla of satellites identifying the warmest parts of all 2 965 500 square kilometres of the Mediterranean on a daily basis.
An updated map of the sea surface temperature (SST) of the world's largest inland sea is generated every day as part of ESA's Medspiration project, with an unprecedented spatial resolution of two square kilometres, high enough to detect detailed features like eddies, fronts and plumes within the surface temperature distribution.
The animation above shows the last six months in the life of the Mediterranean, right up to yesterday, as the waters warm up from the depths of winter to the start of summer.
"Every day at 1200, a two-kilometre resolution map of SST is produced over the whole of the Mediterranean sea, " explains Gilles Larnicol of Medspiration partner CLS (Collecte Localisation Satellites). " This is the first time such a fine resolution has been reached, and a large number of satellite sensors are involved in the analysis method based on optimal interpolation. Medspiration uses data from six different sensors – two European, two American and two Japanese.
"The animation shows the winter cooling of SST that propagates eastward. Superimposed on this large-scale seasonal signal, we can also clearly observe the signature of well-known medium-sized or 'mesoscale' structures.
"These include the Alboran gyre found east of Gibraltar and eddies in the Algerian and Levantine basins, in the west and east Mediterranean respectively. Lastly, the high resolution of the products allows us to detect small features such the discharge of the Po River into the Adriatic, which evolves as a steep coastal current along the Italian coastline."
Medspiration utilises data from the Advanced Along Track Scanning Radiometer (AATSR) on Envisat, the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) on Meteosat-8, two Advanced Very High Resolution Radiometer (AVHRR) sensors on US NOAA polar orbiters, and a pair of Japanese-built instruments, the Advanced Microwave Scanning Radiometer (AMSR) and TRMM TRMM Microwave Imager (TMI) instruments, aboard NASA's Aqua and the JAXA-NASA Tropical Rainfall Measuring Mission (TRMM) spacecraft respectively.
Working like thermometers in the sky, these satellites measure SST on an ongoing basis. For example, Envisat's AATSR uses infrared wavelengths to acquire SST for a square kilometre of ocean to an accuracy of 0.2°C. Other satellites may have decreased accuracy or resolution by comparison, but make up for it with cloud-piercing microwave abilities or much larger measuring 'footprints'.
Medspiration combines data from all these sensors to produce a reliable set of SST data, suitable for assimilation into ocean forecasting models of the waters around Europe and also the whole of the Atlantic Ocean (to a spatial resolution of ten square kilometres). SST is an important variable for weather forecasting and is increasingly seen as a key indicator of the extent of climate change.
Overall results from the Medspiration project feed into an even more ambitious scheme to combine all available SST data into a worldwide high-resolution product known as the Global Ocean Data Assimilation Experiment (GODAE) High-Resolution Sea Surface Temperature Pilot Project (GHRSST-PP).
Its aim is to deliver to the user community a new generation of highly accurate worldwide SST products with a spatial resolution of less than ten kilometres every six hours.
"Interpolated SST maps are of fundamental importance to improve marine weather forecasts," says Rosalira Santoleri of the Italian National Research Council (CNR), part of the Medspiration team. "They are operationally assimilated into numerical models and allow a better initialisation of the surface fields.
"Marine forecasts are essential for many aspects of risk management related to human activities in the ocean and along the seashore. This data promises to improve both oceanic and atmospheric forecasting, as well as our understanding of oceanic processes themselves."
ESA has initiated Medspiration as the European component of GHRSST-PP. It is also funding a GHRSST-PP International Project Office located at the Hadley Centre for Climate Prediction and Research, part of the UK Met Office in Exeter.
As well as ESA, CLS and CNR, the Medspiration team comprises the Southampton Oceanography Centre, the UK-based VEGA company, Meteo-France's Centre for Space Meteorology, the French Research Institute for Exploitation of the Sea (IFREMER), the France-based Actimar firm and the Norwegian Meteorological Institute.
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