NEW: Capital city zoom-ins
These higher-resolution maps of sea surface temperature and currents are designed for being viewed as animations. For every overpass of a NOAA satellite, we generate a new image frame which is the previous one updated only where there are data in clear-sky regions. This makes an animation that is rich in detail of ocean currents in some places, at the cost of being unintelligible in others. View the animation several times and your eye will be able to see the movements of ocean features amongst the noise associated with uncorrected atmospheric and time-of-day (solar heating) influences.
To view the animations you will need software to play fli-format files, eg Quicktime or Aawin [help]. The animations are all updated twice a day, and show the last 7 days of imagery. The individual frames are also provided for users with only low-bandwidth connections, and for printing.
Overlain on the temperature imagery are the sea level (contours at 0.1m; see description below), the geostrophic current velocity derived from that, and the positions of Surface Velocity Programme drifters and deep-drifting, surface-profiling Argo floats (FFI: [data sources]). The arrows show how far the water at the base of the arrow would move in 24h (if it were going straight ahead). Note that the sea level information is a few days older than the latest temperature image, because it takes many days for the altimeters to sample the globe.
Some AVI format examples of recent clear-sky periods:
[Perth, 7 Nov 2004] [Perth, 14-15 Nov 2004]
Regional maps - left panel
The colour-coded field is a map of tidal-residual, isostatically-adjusted [?]sea level anomaly, valid for the analysis date T_a shown, which is normally five days ago. By 'tidal residual', we mean that the (relatively) rapid oscillations of sea level associated with tides are excluded. By 'anomaly', we mean the difference from the long-term average. The atmospheric pressure map (blue contours are lows, white contours are high) used for making the isostatic adjustment is shown because features of the circulation (eg near the coast, or under a tropical cyclone) can sometimes be explained by the winds.
How do we know that the ocean has areas where the water is raised or lowered by half a meter or so, for 100's of km?. If you look closely, you will see lines of little white, magenta or black dots. These lines show where satellites carrying radar altimeters have flown over, measuring the distance from the satellite down to the water. That distance is a little shorter where the sea level is raised a bit. The fact that that difference can be accurately measured is a great triumph of engineering, and is one of the key breakthroughs responsible for the present revolution in ocean observation. The colour of the dot indicates when the satellite flew over. White means more recently than T_a, magenta means the three days previous, black means longer ago.
The four satellites presently (December 2004) flying altimetry missions are called Topex/Poseidon, Jason-1, Geosat Follow-On and Envisat (FFI: [data sources]). The bar plot shows the history, from 7 days before, to 3 days after T_a, of the daily number of observations made by each of these, within the region shown. (More precisely, each sea level 'observation' is a 2km-wide average along 25km of the flight path). The satellites can't sample the whole world every day because they can only measure directly beneath them. To make a complete 'quasi-synoptic' map, we must therefore use data that is up to 10 days old. The ocean changes more slowly than the atmosphere, so that is OK. The older data points are down-weighted compared to the newer ones in making the map. Where there is only old data or no data at all, the estimated anomaly relaxes to zero and the map is obviously least useful.
The other (and much older) way of measuring sea level is by tide gauge. Australia has many of these in ports all around the country. (FFI: [data sources]). We include these data in our maps by averaging-out the tides and making the same atmospheric pressure correction as with the altimeter estimates, then interpolating the results at many points along the coastline between the gauges. Both the observed and interpolated coastal observations are shown on the map. Coastal sea level changes more rapidly than deep-ocean sealevel, so it is just as well that the coastal observations are made much more frequently than those by satellite over the deep sea.
if you didn't get it the sea surface temperature and ocean current maps generated be NOAA are the best for your question.