Aviso Altimetry Information about ocean features seen by altimetry satellites. Aviso logo ffffffff 1 http://www.aviso.oceanobs.com/fileadmin/images/applications/ge/logo_aviso.jpg Mean Dynamic Topography scale ffffffff 1 http://www.aviso.oceanobs.com/fileadmin/images/applications/ge/topdyn_glob_scale.png -65 26 11400000 Mean Dynamic Topography Background map http://www.aviso.oceanobs.com/fileadmin/images/applications/ge/topdyn_globmed.png 0 -90 360 90 Mean Dynamic Topography Gulf Stream Gulf Stream 1 Gulf Stream

The Gulf Stream is one of the major currents on Earth. It comes from The Gulf of Mexico and circulates around a gyre ( materialized by altimetric dynamic topography as a huge "hill" on the ocean surface, top) at its edges. It is highly turbulent, and series of meanders and eddies are seen around the main flow, seen on altimetry sea level anomalies maps (middle and bottom).

Absolute Dynamic topography (merging data from different satellites), 2008/08/02

Sea Level Anomalies (merging data from different satellites), 2008/08/02

Absolute Dynamic topography, 2008/07/01, view updated maps on Sea Views.

Aviso Web site, Large-scale circulation

]]> -65 38 3100000 #test -65,38 Kuroshio Kuroshio 1 Kuroshio

The Kuroshio (or Kuro-Shivo, the 'black river' in Japanese) is one of the major currents on Earth; It circulates around a gyre (materialized by altimetric dynamic topography as a huge "hill" on the ocean surface, top), at its edges. It is highly turbulent, and series of meanders and eddies are seen around the main flow, seen on altimetry sea level anomalies maps (middle and bottom).

Absolute Dynamic topography (merging data from different satellites), 2008/08/02

Sea Level Anomalies (merging data from different satellites), 2008/08/02

Absolute Dynamic topography, 2008/07/01, view updated maps on Sea Views.

Aviso Web site, Large-scale circulation

]]> 147 33 3100000 #test 147,33 Bathymetry and currents Bathymetry and currents 1 Bathymetry and currents in the Zapiola area

Currents do not circulate randomly; they obey the laws of physics, which compel them. The bottom topography is one of these constraints that have the currents deviating, separating or speeding up.
The Argentine Basin in the South Atlantic Ocean is one of the most energetic regions in the ocean with complex dynamics. This region plays an important role in the global climate. Two features can be observed. On the continental plateau, in shallow waters, the confluence between the Brazil Current (poleward current) and the Malvinas Current (ascending current) around 55�W, 40�S form a strong frontal structure with high energy. In deep waters, an intense anticyclonic gyre around the Zapiola Rise in the center of the basin (45�W, 45�S).

Bathymetry from ETOPO2 and red arrows for currents. BMC = Brazil-Malvinas Confluence, ZD = Zapiola Drift.

Mean Dynamic Topography and mean geostropic velocities in the Zapiola area.

Eddy Kinetic Energy calculated from the altimetry, January 23, 2008

Aviso Web site

]]> -50 -42 3100000 #test -50,-42 Geoid Geoid 1 Geoid

On the oceans, the geoid coincides with the mean sea surface, i.e. with a calm ocean surface, with no tides, winds nor even Earth roation (The geoid is defined as an equipotential surface of the Earth's gravity field). Thus, a bump on the geoid corresponds to an excess of mass, for example a relief on the bottom ocean, while an ocean trench, associated to a mass deficit, creates a depression. Since they are measuring very precisely the ocean undulations, the altimetry satellites make it possible to map the geoid.
The highest geoid heights and those most visible on a map, reflect deeply-buried density variations. Heights range from a low of -110 meters (magenta) in the Indian Ocean to a high of 85 meters (red) in Eastern Pacific. Even at 5' resolution, some beautiful features of the geoid are obvious: the major trench and ridge systems, islands, seamounts...

Geoid height (EGM08) with respect to reference ellipsoid.

Aviso Web site, Geodesy and geophysics applications

]]> 78 0 3100000 #test 78,0 Tehuantepec eddies Tehuantepec eddies 1 Tehuantepec eddies

In winter, winds blow by pulses through a mountain pass across the Tehuantepec Isthmus (Mexico) to fan out over the Mexican Pacific in the center of the Gulf of Tehuantepec, generating large mesoscale eddies. Their sea-level signature can be tracked as far as 140�W (equivalent to 220�, on the western site of the map above) before it disappears during the summer (the eddy season begins in late October and lasts approximately 250 days until early July), coinciding with the strengthening of the North Equatorial Countercurrent. Continuous series of altimetry data show that five to six eddies are generated on average off the Gulfs of Tehuantepec, Mexico and Papagayo (Nicaragua) each year. Such ocean features have a large-scale impact on the Eastern Pacific.

Sea Level Anomalies (merging data from different satellites), March 07, 2007. Four, then five, warm, anticyclonic eddies can be seen propagating westward. Click here to see an animation over the first four months of 2007.

Aviso Web site, Mesoscale circulation

]]> -98 12 3100000 #test -98,12 Agulhas rings Agulhas rings 1 Agulhas rings

The Agulhas eddies are formed by the Retroflection of the Agulhas current, which runs along the southeastern coast of the African continent. The Agulhas system has an intense mesoscale activity. It is a key region to understand how the ocean affects global climate on two counts: first, because it moves warm waters from the Indian Ocean towards the Atlantic, thus maintaining the global thermohaline circulation; and second, because it plays an active role in the carbon cycle by absorbing carbon dioxide.

Sea Level Anomalies (merging data from different satellites), January 23, 2008.

Eddy Kinetic Energy calculated from altimetry, January 23, 2008. This ocean area is very turbulent and shows strong eddy kinetic activity.

Aviso Web site, Mesoscale circulation

]]> 20 -38 3100000 #test 20,-38 Southern ocean Southern Ocean 1 Southern Ocean

The Antarctic Circumpolar Current is unique since it is the only current not bounded by a continent, thus allowing water to flow between oceans. It connects the Atlantic, Pacific and Indian Ocean basins. The Antarctic Circumpolar Current's eastward flow is driven by strong westerly wind, around a low of the Dynamic Topography. It transports more water than any other current, even if it is slower than some other currents (Gulf Stream, Kuroshio), and extends from the sea surface to depths of 2000-4000 m and can be as wide as 2000 km. Since it is cold, it keeps warm ocean waters away from Antarctica, helping that continent to maintain its huge ice sheet.

Sea Level Anomalies in the Southern Ocean (merging data from different satellites), 2008/11/30. Click here to see an animation over 2008.

Mean Dynamic Topography and mean geostrophic velocities in the Southern Ocean

Aviso Web site, Southern Ocean

]]> 0 -55 3100000 #test 0,-55 Mean Sea Level Mean Sea Level 1 Mean Sea Level over the Mediterranean Sea

Multi-mission sea level trend in mm/year in the Mediterranean Sea for October 1992 to February 2009 (Credits CLS/Legos).

Global mean Sea Level rise is one of the consequences of global warming. Altimetry satellites are a crucial help for observing variations in mean sea level. With more and more data, we can confirm trends, and attempt to mitigate their effects. Altimeter measurements show that between 1992 and 2009, the global mean sea level rise amounted about 3 mm/yr whereas this increase did not exceed 1.8 mm/yr over the XXth century. These measurements are a global average, but in fact the rising sea level is far from uniform and regional trends are observed. At the scale of the Mediterranean Sea, the sea level in the Eastern Mediterranean basin has risen significantly in recent years, due to warmer water temperatures (observed by in-situ measurements). But if we look at the Ionian Sea off the tip of Italy, data acquired by satellite altimetry show that sea level in fact fell.

Aviso Web site, Mean Sea Level

]]> 15 37 3100000 #test 15,37 El Ni�o El Ni�o 1 El Ni�o

Merged Sea Level Anomalies in Tropical Pacific on November 12, 1997

El Ni�o and La Ni�a are the names of climate events occurring in the tropical Pacific Ocean, which are now globally infamous. They characterise a close relationship between the ocean and the atmosphere, in which the main protagonists can have devastating consequences worldwide. Satellite altimetry, which measures sea surface height (which rises with higher temperatures during El Ni�o or falls with colder temperatures during La Ni�a), is vital for the early detection, analysis and close monitoring of these phenomena.

View an animation on Google Earth of the major El Ni�o / La Ni�a events in 1997-1998. Choose your time resolution by clicking on one of the El Ni�o sub-directories in the left menu: an animation in low resolution (4 Mo, one image per month) or an animation in high resolution (26 Mo, three images per month). Then, launch the animation using the time slider, and if necessary, delete the background display by clicking on Mean Dynamic Topography in the left menu. The download time may be long depending on your connection and not be enough while the first frames are playing. Take time to download all images on an entire first play and then restart.

Aviso Web site, El Ni�o bulletin.

]]> -160 0 3100000 #test -160,0 High resolution 0 1 http://www.aviso.oceanobs.com/fileadmin/documents/applications/anim_ENSO_hr.kml onInterval -160 0 7310000 Low resolution 0 1 http://www.aviso.oceanobs.com/fileadmin/documents/applications/anim_ENSO_lr.kml onUpdate -160 0 7310000 Ocean seasons Ocean seasons 1 Ocean seasons

Climatological monthly MSLA for January (top) and July (bottom) on Indian Ocean (calculated by averaging the weekly maps of delayed-time sea level anomalies over a same month from December 1992 to January 2009. Credits CLS).

The alternation of the seasons is the main cause of changes in sea level during a year. It's a simple phenomenon : surface temperature increases as a result of solar radiation, the heat propagates in-depth and while it warms up, there's a water's dilatation. Conversely, if the surface temperature drops, there's water's contraction. This is called the steric effect. But, oceans and continents do not warm up or cool at the same time, we observe a temperature difference between both which is the cause of atmospheric convective systems with a seasonal shift. The monsoon current in the Indian Ocean is a good example. The wet Indian monsoon lasts from May to September as a result of the temperature contrast between the continent (very hot in summer) and the Indian Ocean (colder). This contrast leads South-Westerlies winds in the Sea of Oman and South-Easterlies in the Sea of Bengal, bringing a warm and wet air, which converge on the Himalayas and condense as welcome rains. By making long series of climatic sea level (here, over 16 years of altimetric measurements), we can highlight recurring phenomena and therefore see this seasonal cycle, all the more reliable since the series of measurements is long. The monthly average for July (bottom) over 16 years of measurements of sea level shows that the Indian Ocean is more dilated (colors red and orange in the basins of Oman and Bengal)) than during the months of January (top).

Aviso Web site, Data, Monthly mean and Climatology Maps of Sea Level Anomalies.

]]> 67 10 3100000 #test 67,10