Chapter Three

Typical distributions of water characteristics

Example 4B: Surface properties of world ocean waters

DPO textbook references for Surface properties of World Ocean waters:

DPO 4.2.1 Surface temperature
DPO 4.3.1 Surface salinity
DPO 4.4.1 Density at the sea surface and in the upper layer
DPO 4.5 Dissolved Oxygen (at surface)
DPO 4.6 Nutrients and other tracers (at surface)

The DPO maps of surface temperature, salinity, and surface density in winter, and surface nitrate (DPO Figures 4.1, 4.13, 4.16, and 4.22, respectively ) provide a view of the global distributions of key ocean surface property distributions. We will use JOA to make similar maps, using data from the World Ocean Atlas data compilation.

(In the example below, you may wish to occasionally refer to the Chapter 3 DPO JOA Examples for some of the basics regarding JOA map plots.)


Warning: data file may slow your computer!

The data file used for these “surface properties” examples is large relative to the relatively slow speed and relatively large memory usage of the Java environment.

Files that may be needed or created in this example:

  • WOA05_surface.jos

Exercise 4B-01: Data Files - Importing a Spreadsheet

  • Start JOA
  • File → Open…WOA05_surface.jos

    WOA05_surface.jos is a text data file. Due to a JOA software limitation they contain too many stations (grid points in this case) to be opened if they are in JOA binary format.

  • JOA will then present you with the JOA Spreadsheet Import Options dialog box:


    FIG 4b-01 Spreadsheet Import Options dialog box


    Because this .jos data file is in tab-delimited format with the default (-99) JOA missing value markers, all you need to do here is to click on OK. JOA will then open the .jos data file into a standard JOA Data Window.


    If JOA on your computer cannot open the file WOA09_surface.jos, or this file severely slows down your computer, you might try opening, instead, the file WOA09_surface_reduced.jos, which is somewhat smaller.

  • Click OK

    The resulting JOA Data Window will look something like this:


    FIG 4b-02 Java OceanAtlas Data Window

We wish to make maps of the World Ocean onto which we can plot these data. At this writing, JOA does not offer the Robinson map projection used to make DPO Figures 4.1, 4.9, 4.15, 4.19, and 4.23. The two global JOA map projections - Mercator and Miller Cylindrical - are highly distorted at high latitudes. But JOA can have as many map plots open simultaneously as computer resources permit, so here we provide instructions to make two map plots, which together cover most of the World Ocean.

Exercise 4B-02: Surface Properties - Making a Lambert Azimuthal Equal Area Map Plot

These are maps of salinity at the sea surface (0 meters or 0 decibars) from the multi-year average World Ocean Atlas (WOA) data set.

Exercise 4B-03: Surface Properties - Examining Lambert Azimuthal Equal Area Map Plots

Via the Configure Map Plot dialog box's Station Colors panel, you can select any other property and a corresponding color bar. We suggest these pairings to show off World Ocean characteristics:



Regarding use of the PRES-0-6000_srf.xml Surface on this panel: In order to plot/color data values at stations, JOA must interpolate data onto surfaces - even if data values are already present in the data file on the desired surface. (Also, in this example, there are data present on only one surface, i.e. 0 dbar).

Hence one must select a preconfigured Surface onto which JOA interpolates the data. (See the JOA User Guide in the <%= link_to "JOA application tab", "/joa" %> for instructions on making your own custom preconfigured Surface for interpolations. You can make Surfaces for any JOA parameter, including parameters in the data file, calculated parameters, and custom-calculated parameters.)

Remember, now that you have these map plots ready, you can explore the surface ocean with them in multiple ways.

  • You can click on data points to read and compare data values in the Data Window.
  • You can select sub-areas of plots (via the standard point-click-hold-move-release mouse sequence most computer applications use for selections) and JOA will make those into new plots, which can be reconfigured as you wish.
  • You can change or shift projections. (Hint: Try the two polar projections.)
  • You can even have multiple map plots of the same area, each configured to show a different parameter so that you can explore how the various oceanographic parameters co-relate.
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