Home > 9. Operational/Synoptic > 9.9 HYCOM Download
9.9 Visualizing Ocean Model Scalars & Vectors in IDV: HYCOM Download
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| 1. Open the HYCOM main website and take a few minutes to read about the whole program and its achievements. |  |
| 2. Just below this welcome, on the same page, you can read an overview of the 3 major data product lines available. We're most interested in the first of these. |
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3. Click on the DATA SERVER link at the top of the page. But don't click on any of the 3 sub-links that appear.
This is actually the same link as the HYCOM Data Servers link in the prefatory materials above; it's just a bit awkward to find, so we wanted to show you the single place where it is actually found in the website. |
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4. A long page with many sections appears. Near the bottom you'll find these 6 access method links. We're going to use the highlighted one, NCSS; the link is actually clickable here also.
Click on the NCSS link. This begins a sequence of 4 necessary menu pages that all lead to the data you want. |
Access Method
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5. Not shown on this page or the next ones, there is a useful gloss on a different HYCOM explaining the filename codes A and U for the datasets to follow:
We would prefer to work with the U files, for the sake of simplicity, but in the links below only the A files are actually served up by the NCSS. The U files are globally aggregated, and defeat the purpose of this exercise. |
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| 6. Click on the NCSS URL. |  |
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7. Click on GLBA0.08/EXPT 9.1 (LATEST 10 DAYS) WITH FORECASTS in the first group of experiments.
NOTE: Of course you may chose the second item, if you want a longer time period. These instructions are just suggestions. |
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8. Click on ALL LATEST DATA AT 00Z.
What do these acronyms (e.g. MLT) mean? See below. |
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| 9. Click on the NETCDF SUBSET link. |  |
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10. This is the actual NCSS form. It is quite large, so we'll work with the separate sections, beginning with the choice of parameters which you see here:
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11. In the SPATIAL SUBSET area, we enter the familiar coordinates for Liberia (or whatever you want.
NOTE: The graphic interface seems perfectly happy with several different range schema for the longitudes, including 0-360. |
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12. Enter an integer value for HORIZONTAL STRIDE if you want to obtain a subset, e.g. 3 = every third point. Check the box if you want to disable a previous non-zero value.
Leave it untouched to get all points. |
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13. For TIME SUBSET, set the range you desire. You can also use striding (as above) for obtaining a temporal subset.
Leave it untouched to get all times. |
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14. For VERTICAL LEVEL, insert whatever values you want from the complete list seen in the panel above.
Leave it untouched to get all levels. But watch out for a huge number of separate level objects in Saga, if that's your intended display platform. |
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| 15. The resulting file will be fine for IDV and ncBrowse plotting, without additional LAT and LON variables. But you may need these for some purposes, and if so you should check the ADD LAT/LON control. |  |
| 16. Finally, unless you have expertise with NetCDF4, it would be advisable to select FORMAT = NETCDF. |  |
| 17. Then click SUBMIT at the bottom of the form to proceed. When the NCSS tool is working, then you should get a dialogue box to locate and name the resulting NC file. Good luck, because this tool is known to hang up or give error messages at this point. Just keep trying. | |
18. When and if you get a result, then save it in the folder DATA > OCEAN > HYCOM with the filename
Now you can proceed to work with the data in IDV. |
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| 19. Run IDV. |  |
| 20. In the DATA CHOOSER, use these settings, then locate the TUV file you just downloaded. Then click ADD SOURCE. |  |
| 21. Make these selections, then click CREATE DISPLAY. |  |
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22. Before you even look a the new map, use the DISPLAYS settings to set COLOR TABLE to the familiar RADAR > DBZ palette.
Then select COLOR > DBZ > CHANGE RANGE to use the FROM ALL DATA option. |
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23. Now you can see the surface temperature in the Liberia area with a really good palette.
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24. You can use the VIEW > CAPTURE > MOVIE controls to animate the data sequence, as you see here.
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| 25. Now we'll make vector arrows for the data grids. We know we can do this because we ordered U and V vector component grids, above. | |
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26. In IDV, open the DERIVED option (left unopened above) and select the FIELDS > FLOW VECTORS option.
On the right side, select DISPLAYS > FLOW DISPLAYS > VECTOR PLAN VIEW. Then click CREATE DISPLAY. |
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27. UNCHECK the PLAN VIEWS > TEMPERATURE map on the right-hand list of objects so you can see the vectors. This is our first view of the vectors, which usually requires additional work to look good. There are too may arrows and they are too small.
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28. Click on the FLOW DISPLAYS > FLOW VECTORS object in the right-hand list, to see its properties.
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| 29. This is the final vectors display. |  |
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30. And here you can combine the displays by CHECKING the PLAN VIEWS > TEMPERATURE again, and changing the vector COLOR to BLACK. It is easy also to make an animation like this.
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| 31. Of course you should save the IDV data analyses as XIDV files in the folder PRODUCTS > IDV > XIDV and perhaps your animations there or in a special other folder. | |
