Visualizing Modeled Wave Analysis Grids in IDV: WW3
Abstract: This new
version of the exercise does not require the confusing navigation
through the WW3 website and its various data access methods.
Fortunately access through THREDDS is now possible, and the user --
after initial orientation hrough the WW3 website, of course -- can move
directly to easy digital product access. The products are provided
from the source site in the notorious GRIB format -- not well known to most marine scientists -- but easy to
subset, download and plot with IDV. THIS LESSON IS PROVIDED FOR
EDUCATIONAL PURPOSES ONLY. NO ONE SHOULD ATTEMPT TO RELY ON THESE
ANALYSIS PRODUCTS FOR NAVIGATION OR FOR ANY OPERATIONAL PURPOSES AT SEA.
Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
|1. WW3 is a very
widely used and respected model, used by the military and global shipping
interests. Go through this lesson now, but please come back to the
site for more detailed study. Open
NOAA Wave Watch III (WW3),
and take some time to read about the model.
|2. This is the map key to the
products, at that website. Links to descriptions of the individual
products are provided below it: GLOBAL, HURRICANE, GREAT LAKES, GLOBAL
Click the WW3 Model Data Access link (top
|3. And this is the Model Data
Access page. Notice that most of the available products are in FTP
|4. The remaining
panels of this exercise use instead direct access to the files via THREDDS
(not even mentioned above). Direct THREDDS access is provided by the
US National Center for Environmental Prediction (NCEP) alongside the above
products. We can use these data through the CATALOG feature in IDV.
|5. Run the latest, properly
set up version of IDV, and select a global map with PROJECTIONS > PREDEFINED
|6. On the dashboard page,
make these settings to get to the NCEP THREDDS data products. If this
is your first use of the catalog approach, take the time to do a little
Then click on the PLUS SIGN (+) beside WWW3-GLOBAL.
As far as this author knows, there is no generalized search function for the
data types in the catalogs, only words/phrases in the HELP File. So
unfortunately you must rely on tips from friends and MDL to identify data
accessible to IDV.
|8. You can open the various
folders at WW3 to see what's there. Unfortunately the data items
(blocked here in blue) are not particularly well-described by the online
documentation. Just below begins a sequence of products identified by
dates, which is what we usually expect.
NOTE: Please see that the earliest file
in the date sequence was created in October 27,
2014. Today's date (for the author) is November 10, 2014, so the files
are kept in place for about 2 weeks. Here's the simulations they
- Today and the next 4 days: Every 3 hours
- Following 3 days: Every 6 hours
Below, we'll see what they show.
|9. Go to the latest simulation grid
(today's date, in the case of the author). Burrow down into the folder until
you find an item that causes the ADD SOURCE control to activate (gray to
black) and select it.
Click on ADD
|10. Find the wave grid you
just selected in the DATA SOURCES panel. Right-click on it and select
|11. Select the SPATIAL SUBSET
tab along the top. This is the main method to subset a global source
to a specific area.
|12. Use the cursor to draw a
box anywhere on the map. This is not your actual choice; it just
activates the control.
Then enter the actual coordinates of the Liberia
area (or whatever you want) in the 4 available spaces.
NOTE: There are other controls (tabs along the top) you can use
here or later. But the spatial subsetting must be done here.
Now click OK.
13. Now you can open up the FIELDS and DISPLAYS PANELS to access the
data. Make these choices, but come back later to explore all of them
to see if you like something else better.
In the list of
available parameters (2D GRIDS), select the one you want. The
author chose combined wind and swell wave height. [Get adventurous
and examine the MOMENTUM group to see what's there.]
In the upper
right panel, select the display view you like. Later, try more
than one to see how it works.
In the lower
right panel you can select the TIMES by changing USE DEFAULT to USE
SELECTED. Don't use the REGION tab here, because it doesn't allow
exact coordinates. The DATA SAMPLING tab lets you step through the
data, i.e. every nth cell, to reduce processing time.
single date. Then click CREATE DISPLAY.
Then click on CREATE
|14. This data map should
appear. If it's not quite right, then UNCHECK the box to hide it, then
go back and make a new one. Keep trying until you understand what's
happening, and you get it right.
|15. When you get the figure
just right, then here's how you "fix" the colors. Click on the map
name (right-hand column of maps) to open the control for it. Select
COLOR TABLE > RADAR > DBZ(NWS) to get the most common rainbow spectrum of
Notice that the wave heights range from 0.6 m to 1.7 m (look at
the top row beside the palette).
|16. This gives a better
distribution of colors so you can see the structure at all speeds.
|17. Click on the same
control, but use CHANGE RANGE to pick rounded values, if you want. For
example the author selected 0 and 2
|18. This is not as colorful
as the above figures, but it is scientifically better, because it uses
values that could be used to accommodate other, related datasets, for
purposes of comparison.
Select the range you like, no matter what the
|19. Now if IDV had a
histogram function (it doesn't) then this is what it would show for these
same data. You can use the method at
5.17 Creating a Histogram in Excel for IDV Grids.
Always examine display grid values
as histograms, if you want to really understand what you have.
|20. If you noticed above, we
selected only one TIME when we used the CREATE DISPLAY control. Here
we've gone back and used all of the times for the same geographic subset.
You can see this by the long string of green time icons along the top-left
side of the map.
You could click on the movie controls just under the
small green boxes, to see an animation.
|21. But we want to save the
animation, for training and display purposes. So select VIEW > CAPTURE
> MOVIE and follow the defaults to capture a TIME ANIMATION.
|22. And here is
the author's animation of these data:
|23. Finally, how can you take
the global or area data and extract a forecast for a particular point?
Select DISPLAYS > DATA PROBE/TIME SERIES for all the data.
|24. Then a small dark cell
will appear on your COLOR-SHADED PLAN VIEW map. You can move it
manually, or by specific coordinates to a desired location. As you
move it, this graph will change to show the wave forecast for that location
within the grid.
THIS CAPABILITY IS
ONLY FOR SCIENTIFIC TRAINING AND DEMONSTRATION, NOT FOR ACTUAL OPERATIONAL
FORECASTING. DO NOT GET YOURSELF IN TROUBLE BY ATTEMPTING TO BECOME A
WEATHER PERSON OVERNIGHT.
|25. Now that you
have the full series of grids and the probe time-series, you can save the
complete collection with FILE > SAVE AS in the folder PRODUCS > IDV > XIDV
with the filename