What the maps show
Depending on the zone, the colour scale for each parameter plotted may vary in minimum and maximum (for example, water temperatures at the equator will be higher than when at the Pole, and the use of the same values for minimum and maximum would hide information). The various palettes of colours have been selected according to what they represent (this choice is not an absolute rule as other projects choose different colours for the same parameters); they are however identical from one beacon to another and from one year to another.
The maps correspond to the date at the end of the Argos beacon's weekly trajectory. The previous week's map may possibly correspond more to the beacon's trajectory if the interesting movements were at the beginning of the week.
Ocean colour
Phytoplankton is the "plant" part of plankton (live micro-organisms in the ocean) that makes up the first link in the marine food-chain. Measuring the amount of phytoplankton is essential for understanding marine ecosystems. The presence of phytoplankton modifies the colour of sea water because it contains chlorophyll, the pigment which makes the Earth's vegetation green. These instruments are sensitive to weather conditions: when the sky is overcast, maps have white zones which indicate where measurements are blocked by clouds. More information on ocean colour and chlorophyll measurements | ) |
Surface currents
Surface currents are calculated using either the geostrophic currents and ocean surface winds, or oceanic forecast models such as Mercator.
More information on currents
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Surface winds
Winds not only make the buoys move, they also influence the surface currents. They can be measured using instruments called "scatterometers" carried by satellites, or calculated using meteorological forecast models such as those at Météo France.
More information on surface wind
Ocean topography
This refers to the relief of the oceans' surface due to currents and their variations. For example, we can observe ocean eddies shown as "hollows" (cold eddies) or "bumps" (hot eddies) of this relief. More on topography (or height) of the ocean | ) |
Sea surface temperature
Surface temperature can be measured by buoys at sea, by satellites or calculated using oceanic forecast models such as Mercator.
More information on sea surface temperature
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Wave heights
Waves are among the phenomena the most feared by sailors. They can be measured using instruments carried by satellites, or calculated using meteorological forecast models such as those at Météo France.
More information on wave heights
Concentration of ice, thickness of ice, ice drift
Sea ice (or ice floe) can be characterised using different data. The Mercator model calculates in particular
- concentration of ice: from 0 to 1 (in reality, from 0 to 100%) of the surface covered by ice.
These amounts can also be measured by satellite (the concentration and drift through different techniques, or thickness using the Cryosat (ESA) altimetry satellite), or calculated from measurements.
More information on sea ice
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Bathymetry
Bathymetry is the depth of water (the negative distances to the sea floor relief). Depths are measured in certain spots by oceanographic ships, or calculated using satellite altimetry measurements and ship measurements.
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Ocean topography variations
This refers to the variations of the relief of the oceans' surface. For example, we can observe ocean eddies shown as "hollows" (cold eddies) or "bumps" (hot eddies). More on topography (or height) of the ocean | ) |
Salinity
) | The concentration of salts (in the plural, since we are dealing not only with "table" salt, alias sodium chloride but also various dissolved minerals; even though the former accounts for most of the salt content) in sea water is an important piece of information: the more salt there is, the denser the water will be and this plays an important role in its circulation. Salinity can be measured by buoys at sea, derived from other measurements or calculated using oceanic forecast models such as Mercator. Today, the SMOS (ESA) satellite can measure it directly. More information on salinity |