First we need to obtain the data from the TOMS Website. From this site, select "Ozone data-ASCII" format, and a date and press "request". You will need to save the resulting file on your local disk. If you are interested in April, 1998, as we were, you could instead jump directly to the 1998 ASCII data directory on the FTP server. If you have an FTP tool, you might want to use it to download a large number of daily files. We've chosen the 30 files for April.
Next, you need to concatenate these daily files into one large file, which we call ga9804.ept. This file can be put wherever you like, but see the discussion of paths and for more information. On Unix machines, you can use the "cat" command. Any text editor can also be used to place these files one after the other. You will notice that they are structured so that data vary fastest in longitude (for a single latitude starting at -89.5). The data vary next with latitude and since we have concatenated these files together, the resultant file varies slowest in time. There are 288 longitude points (-179.375 to 179.375), 180 latitude points (-89.5 to 89.5) and 30 time points (days). Also, in each of the original daily files, data values appear after 3 header lines and each data line has a blank space at the beginning followed by 25- 3 digit numbers with no spaces in between. There are 11 such lines followed by a similar line but with only 13-3 digit numbers. Then the whole process repeats. To read this file, the following text must be added to the appropriate (e.g. in the "TOMS MONTHLY" folder in the "Earth" folder) folder in the datamanager.txt file:
DataSource "April, 1998 TOMS" file "ga9804.ept" format "Ascii" schema "start:" "3/" "180(11(x,25I3/),x,13I3/)" "goto start" endschema inputorder "1-23,123" converter "Linear" meta "Time" "days" axis 3 entries 30 range 1.0 30.0 meta "Longitude" "degrees" axis 1 entries 288 range -179.375 179.375 meta "latitude" "degrees" axis 2 entries 180 range 89.5 -89.5 meta "ozone" "du" axis 0 entries 256 range 0.0 595.0 colorhint "cutten"
With the above keywords in your datamanager.txt file, you are ready
to start WebWinds.
From the "File" menu, select "Open". From the resulting Data
Directory window, double click "Earth", then "TOMS MONTHLY". Under
"Data Source Descriptions",
double click "April, 1998 TOMS". Next click the "Load" button in
the object window that appears and watch the progress bar at the top turn
green. You should then have the following Data
Next, select "Image" from the "Tools" menu on the Desktop. You can also select a "Slider" from the same "Tools" menu. Once the "Status" of the TOMS object is "Loaded", drag it into the image, then drag it into the slider. Next, link the slider into the image and click the "Magnify" button on the image to get an image similar to the one below. Next, move the (time) slider back and forth. You may (depending on your computer) have to turn tracking off (click the "track" button). You will notice 2 items of interest: the column ozone varies from day-to-day in a way that mimics the weather patterns, especially at high latitudes. This is a well known effect. What is less well known is the source of the features that remain stationary as you move the slider. If these features look vaguely familiar, try selecting "coast 180" from the "Overlays" menu on the image. The resulting image looks like:
Notice that one feature correlates perfectly with the mountains along the west coast of South America.
There are a number of other tools that can be used with this data object. Select "Profile" from the "Tools" menu on the Desktop. Next, drag the image into the profile. Select "Draw profile line" from the image "Menu" button and move the cursor to the image window. While holding the mouse button down, move the mouse across the image. A line will appear on the image which shows the area where the TOMS ozone are depicted in the profile:
Notice that all windows update if the slider is moved.
A number of other tools can be used here including Value
View and Track Pixel. When you
exit from this WebWinds session, remember to save your work.