Friday, 23 September 2011

Geography Picture of the Week - Highest resolution global map of ocean surface salinity

First up, the most observant of you will notice that I have changed my 'Geography Picture of the Day' to 'Geography Picture of the Week' as, in reflection, it was always high unlikely that I would post a picture everyday! Instead, hopefully, I will be more likely to post one weekly and although I am guessing that most will be linked to physical geography, I will try and find some relevant to our current human module........

So, what is my Geography Picture of the Week this week???

I apologise to any of you who are getting fed up with oceanography-related posts (my EPQ will be over very soon so hopefully I won't be so tempted to write about oceanography stuff all the time when I should really be writing about Development and Globalisation!) but I really couldn't resist posting this one!!!

The above image was released by NASA and represents the one of the first and high resolution global map of ocean surface salinity made, using data acquired by the Aquarius/SAC-D satellite, launched in June this year with the map itself only incorporating the first 2 and 1/2 weeks of data since Aquarius became operational on the 25th August. Scientists have been able to measure ocean salinity for decades by lowering instruments from ships or by deploying robotic floats, but the technology to gather data from orbit is a recent innovation.

The generation of this map has been long anticpated by oceanographers and meterologists so I am guessing there are a few very happy scientists around the world at the moment! If you have followed any of my highly unorganised posts on oceanography you might be able to appreciate why........

Well, our ability to map and thus determine salinity (basically the 'saltiness') will improve our understanding of ocean circulation, the risks of future alterations to it and also an understanding of a few key climatic processes (note that the oceans and atmospheres are incredibly closely coupled with, in simple terms, the oceans provided the memory for the climatic signals generated in the atmosphere).

So, what excatly does this map show? Well, the red and yellow colours represent areas of high salinity with blues and purples denoting those with low salinity and black showing areas with no data(note no data retrival on land). The maps clearly shows well-established, large scale features, significantly the major salinity differences between the Atlantic, Pacific and Indian oceans. With the Pacific ocean by far the 'freshest', supporting the absence of deep-water formation sites, and the Atlantic by far the most saline. The salinity of ocean water is intrinsic to ocean circulation, although most precisely thermohalince circulation, which is soley driven by density differences (salty water is denser than less saline waters and so is forced to sink, thereby helping to drive the circulation). Also apparent is the corespondance between areas of lower salinity and rain belts and the areas of high evaporation found in the subtropics (regions of evaporative enrichment). Smaller-scale features are also possible to identify like the freshwater outflow from the Amazon River which acts to dilute immediate Atlantic surface waters.
The goal of the Aquarius mission is to retrieve salinity with a resolution of 0.2 parts per thousand (a concentration change equivalent to about one millilitre of salt in six litres of water). Aquarius carries three high-precision radio receivers that will record the natural microwave emissions coming up off the water's surface; emssions varying with the electrical conductivity of the water - a property directly related to how much dissolved salt it is carrying.
Smos global salinity map
The Nasa-Conae spacecraft is not the first ocean salinity mission in orbit as Europe already have a satellite in operation (Smos) which was launched in 2009, producing the first ever global salinity maps generated from space. The intention is to inter-calibrate and combine the Aquarius and Smos measurements as, together,these spacecraft are now acquiring volumes of salinity data that dwarf all the information ever gathered in this field of study.

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