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Exercise Title:
Visualizing Modeled Meteorological Products in Integrated Data Viewer (IDV): Global
Forecast System (GFS)
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Abstract: The
Global Forecast System (GFS) products are arguably the most widely used
meteorological simulations, due to their ease of access (through full OPeNDAP compatibility) and the fact that no fees,
licenses or registrations are required. The results are currently
available only in GRIB, but IDV and Panoply can easily manage to display
these results. Below, you'll work with a typical scalar quantity
(surface temperature) and a typical vector quantity (surface wind
vectors). THIS LESSON IS PROVIDED FOR
EDUCATIONAL PURPOSES ONLY. DO NOT RELY ON THESE
PRODUCTS FOR NAVIGATION, FORECASTING OR FOR ANY OPERATIONAL PURPOSES AT SEA.
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Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
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Required Software:
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Other Resources:
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Author: Murray
Brown with big help from Rich Signell
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Version: 1-22-2015
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1. Some users may
encounter problems loading these products at the ADD SOURCE stage (see
below). Be aware that a few very
large data catalogs (e.g. HYCOM) take a long time to load, especially if you
have not selected data subsets by geography (REGION), time, depths or
heights (LEVELS) or data density (STRIDE). |
2. Open the main GFS website
to read more about this major modeling system. It is possibly the most
widely used metocean model in the world. |
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3. The best place to get all
the data, including a new 0.25-degree version, at the NOMADS site.
Open that link and read more about all the many datasets you can find there. |
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4. If you scroll down the
page, you'll find these major sections (collapsed here for clarity). |
Data
Set |
freq |
grib filter |
http |
gds-alt |
Global Models |
Regional Models |
Ocean Models |
External Models |
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5. Now let's look at the
GLOBAL MODELS, as you see here. For most of the models, there are 4
links to see more information. Pick any model and look at the 4 available
sub-pages, to see what's there. |
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6. Find the 0.25-DEGREE
products for GFS, and click on the OPENDAP-ALT link. Somewhere in here
are the links you need to hook up these data with IDV. The folder seems to
have a "rolling" set of folders from 10 days previously to today (for the
author writing this exercise). |
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7. Click on the DIR link by the last
day. This directory of data products opens. There are products
of 2 kinds stored here:
- Single time products, with ANALYSIS AT in the file title
- 10-day products, with STARTING FROM in the file title
Looking closely at the descriptions, we can see the products are produced
at times 00H, 06H, 12H and (presumably) 18H every day. But actually,
as you'll see below, the complete product set includes 3-hourly files. |
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8. For the 5th listed product, a 10-day aggregate, click on the
INFO link to see this typical listing of metadata. [The 165 variables
that follow this segment have been omitted for clarity.]
The URL you need for working in IDV is the first item below
the horizontal line: DATA URL. Copy and save it, because we'll
need it soon
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9. If you open the 6th link above, for the single-time product,
this is what you'll see. You can save this URL also
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10. And here are our two
saved URLs, ready to use in IDV:
- Ten days, Jan 20-Jan 30, 2015:
http://nomads.ncep.noaa.gov:9090/dods/gfs_0p25/gfs20150120/gfs_0p25_12z
- One day, Jan 20, 2015
http://nomads.ncep.noaa.gov:9090/dods/gfs_0p25/gfs20150120/gfs_0p25_12z_anl
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11. Run IDV. Make sure it's the
latest version, properly set up with
Exercise 9.1 |
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12.
On the dashboard panel, select FILE > DATA CHOOSERS > GENERAL > URL.
Then enter the 10-day URL you just found above. Then click ADD SOURCE.
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13. Very quickly, you'll see these 2
categories of FIELDS added.
- 3D GRID - parameters that vary with height and are provided
layer-wise within multidimensional grids
- 2D GRID - parameters given for a single specific height, provided in
separate grids
The 3D group is quite modest |
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14. The 2D group is huge, including
many near-surface variables that are critical for weather and climate
modeling. |
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15. Before we do anything
else, we need to reduce the total possible dataset by subsetting it in space
and time. Otherwise our IDV installation will get bogged down with
huge file downloads, etc. etc. So don't select any variable now. |
16. Right-click on the 0p5 object, and
select PROPERTIES. NOTE: 0p5
is the new, best way to specify "0.5" in a filename. |
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17. This subsetting window opens, with
5 different tabs, as you see here.
- TIMES - Look closely and you'll see that they are actually 3
hours apart. We usually do not select times here, so leave these
alone.
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18. Now we need to do something about
the location. Select this tab:
- SPATIAL SUBSET: We need to select the Liberia area of
interest.
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19. Draw a small rectangle anywhere
on your map. This activates the BOUNDING BOX widget. |
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20. Now enter the correct coordinates
for Liberia in the BOX. You can click APPLY now. |
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21. Now you can select the DISPLAY for
the data (i.e. the type of map), and other possibilities:
- Select DISPLAYS > PLAN VIEWS > COLOR-SHADED PLAN VIEW
- Pick TIMES > USE SELECTED and then select the very latest grid
- REGION is always selected in the upper-left PROPERTIES box, never in
the lower-right box, so ignore it here
- STRIDE can be ignored here; we'll use it later in this exercise
Then click CREATE DISPLAY. |
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22.
This map of surface air temperature appears. You can see the date and
time just above it, as either a series or a single point. The color palette information in the right margin.
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23. The default palette usually isn't a
good choice, so you can click on the palette in the right margin to get
these controls for it. The RADAR > DBZ choice is usually good, because it
is the standard rainbow. |
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24. Here's the result of that choice.
The figure is much more interesting and informative. The
Current Atlases may give you
some inspiration to try to explain it, because SST is sometimes closely
related to circulation systems. |
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25. Now we'll make some wind vectors and add these to the same map.
In the upper left corner find DATA SOURCES > FORMULAS and click it to open a
long list of things you can calculate from the data already loaded.
Find and select MAKE FLOW VECTORS FROM U AND V DATA.
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26. This new windows opens,
asking you to identify specifically which grids are the U (left side) and V
(right side) components to use in the formula. |
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27. Open the U menu of
choices, and find the U component in the 3D group of grids. Just below it,
you can see you now have TIMES choices. Leave them at USE DEFAULT
(i.e. use all times) |
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28. Select the LEVEL tab and
then choose 1000 millibar. Essentially that means 1 bar, or very near
the surface. |
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29. Select the REGION tab to
confirm visually that you are still focusing only on Liberia. |
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30. Select the STRIDE tab to
select a method to thin the data. Select EVERY THIRD POINT, which
gives you only 1/9 of the data, i.e. 1/3 times 1/3. |
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31. On the V side, make all
the same choices, exactly. |
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32. Then click OK at the
bottom of the UV selections window. |
33. After a few moments of calculating, something
similar to this nice wind map appears (depending on the STRIDE you used).
Notice the control for the times appears to be a solid green bar, because it
has so many individual times available. Click at several points to see
the map change over time.
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34. Now, you
should go back to the stage where you specified the wind vectors, and
experiment with the various controls so you get the best figure for your
purposes. You can change the size the arrows, their spacing (with
STRIDE), color, etc. Anything you don't like can be changed. |
35. If you want to make an
animation, then select VIEW > CAPTURE > MOVIE and experiment with the
possibilities. HINT: Select GIF for the output to get the smallest
product file. |
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36. Here is the author's
attempt at a movie of the data above. When you view it at full scale,
the arrows are not pixilated, so don't worry about that. |
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37. Make sure to
save your work. The full IDV map with all settings, can be saved with
FILE > SAVE AS in the folder PRODUCTS > IDV > PROJECTS with the extension
XIDV. the movie can be saved there or in the folder PRODUCTS > IDV >
ANIMATIONS. |