Exercise 1. Energy Balance of the San Marcos Basin

CE 394K.2 Surface Water Hydrology
of Texas at Austin
Spring 2005

3 February 2005

Prepared by David R. Maidment and Jon Goodall

Table of Contents

Goals of the exercise

Computer and data requirements

1. Linking to the North American Regional Reanalysis

2. Select a data source
3.  Prepare a display

4.  Add another data source

5. Map display of the San Marcos basin

6. Data Probe of the San Marcos basin

Goals of the Exercise

The goals of this exercise are for you to become familiar with the Integrated Data Viewer as a way of viewing and querying atmospheric science datasets for the energy balance of the earth, and to construct an energy balance for a typical day in July 2003 for North America, and for a location 29.9ºN and 97.9ºW in the San Marcos basin.


Computer and Data Requirements

Integrated Data Viewer

The Integrated Data Viewer (IDV) is developed by Unidata, http://www.unidata.ucar.edu/ , a program of the Universities Corporation for Atmospheric Research located in Boulder, Colorado.   With the sponsorship of the National Science Foundation, Unidata supplies real-time feeds of atmospheric science information for use in US academic institutions.   IDV is a Java program that can be installed in computers with a variety of operating systems.   For use on machines with the Windows XP operating system, the version InstallAnywhere Windows installer for IDV (Direct3D) V1.1 (idv_1_1_windows_d3d_i586_installer.exe)  is best.   This can be downloaded from http://my.unidata.ucar.edu/content/software/idv/index.html once you have established a user name and password.   To avoid having to do that, you can obtain this version here: IDVinstaller   This is a .exe file.  Click on it to automatically install the program.   This installs the program caller from your Start Menu, as shown below.  IDV is a public domain software program that is available free of charge.  It requires that Java already be installed on the computer on which it will run.

For this exercise, we are going to use historical weather model data from the North American Regional Reanalysis (NARR), http://wwwt.emc.ncep.noaa.gov/mmb/rreanl/index.html which is an archive for 1979 to 2003 developed by running the Eta numerical weather prediction model of the National Centers for Environmental Prediction on an historical database of weather observations.  

To be turned in:  Make a brief summary of the North American Regional Reanalysis – how was it produced, what data summaries does it contain, what is its spatial extent and coverage in time?

Data Files

The data files for this exercise are available at ex1.zip They consist of NARR.xml, an xml file that locates  the North American Regional Reanalysis files, and a shape file of the San Marcos basin in geographic coordinates.


1.  Making the link to the NARR  

The IDV uses an XML file NARR.xml to locate the NARR data.  You will actually be viewing the data while they remain resident in their remote location, not downloading them to a local file.   Copy this NARR.xml file to your local directory.  Open the IDV (use IDV not Globe IDV)


You’ll see a display like the one below with a map of the world.

Select Data/New Data Source,  Make sure you are in the Catalogs section of the Data Selector window, not the Files section.


Hit Select File and then navigate to the location of the NARR.xml file and select it.   Hit Update on the bottom of the Data Selector page to update the list of files available at that location.   You’ll get a display that looks like this:

The NCEP HIRES GFSAVN and MESOETA are current numerical weather prediction models whose data we are not going to use for the moment.   NARR-A describes the physical condition of the atmosphere, while NARR-B stores the energy balance components.  

2.  Select a Data Source

We will use the NARR-B_Monthly_3hr data.  Click on the radio button for this data set to expand it:

and scroll down to the January 2003 dataset, and further expand it:

Click on the “North American Regional Reanlysis B ….” to Add Source or add it to the display as a new data source.  Expand the 2DGrid button see the fields available.

3.  Prepare a Display

Select 3 hr fcst surface downward shortwave radiation flux [w/m^2]   and select from the Display options Color-Shaded Plan View.  

and hit the  button.  You’ll get a display like this:

Click in the Color-Shaded Plan View window on the color ramp

and from the options offered select Bright38

and hit OK to apply it.  Close the Color Shaded Plan View Window and you’ll see a display like this:

which shows that at 00:00:00Z (midnight for Greenwich Mean Time) there is darkness over North America with the last sunlight of the day in the far west in Hawaii.  You have 8 displays available, spaced each three hours:

Select each one and view the progress of the sun across North America during an average day in January 2003.   What you are seeing is the esimated downwave solar radiation for the given hour averaged across all the days of January 2003.

Its good at this point to save the display you’ve created.  To do this, using File/Save As from the main IDV Window and  save the file as SanMarcosNARR.xidv.   The extension .xidv is a signal that this is an IDV map file.

4.  Add Another Data Source

Click on Data/New Data Source and select NARR-B 3hr for July 2003:

Make a new display for this data source and color it similarly to the January one (with Bright38).  You’ll see that you can animate the two images superimposed on top of one another using the animation toolbar .  If you end up with repeated displays of the same dataset, you can get rid of the unwanted ones with the little garbage can on the right hand side of the legend display. 

To be turned in:  Make a display of the downward solar radiation for each of the 3 hr intervals for January 2003 and make a similar series of 8 maps for July 2003.   At what Z time does the maximum solar radiation occur?   Where is the maximum solar radiation located for January?  Where is the maximum solar radiation for July?  The data you are viewing are solar radiation at ground level, not at the top of the atmosphere.  Why is there more solar radiation in the western US during July than in the eastern US?

 5.  Map Display of the San Marcos Basin

Now lets focus in on the San Marcos Basin.  We need a locator map to do this, and we’ll add this in from the IDV map display.  You can add a high resolution map of the US, US County Outlines and US Interstate Highways.

and you’ll get a display with the Hi-Res US like below.

You can use the zoom and arrow tools on the left side of the display to zoom in and center your picture.  If the color of an added map is not what you want, click on Map Display  to bring up an editor that lets you change the map colors. 

To add a map of the San Marcos basin, Add Your Own Map,

You’ll get a display that says “Add a Map”, hit the Browse button

and you’ll get a new window that says Open, Select Files of Type Shape Files (*.shp) at the bottom of the page and you can select individual shape files.  You can then rename the map to San Marcos in the Add a Map window above.   There is a repeated image in the picture below of SanMarcosGeo.shp because there is a SanMarcosGeo.shp.xml file also in the list.  Make sure you choose the .shp file that does not have the .xml extension.

Note that maps must be in geographic coordinates to display correctly in the IDV.  You can zoom in on a view of the San Marcos basin with interstate highways also displayed to give a sense of location (highways around Dallas-Fort Worth, Houston and San Antonio are shown in this map).  It seems that the IDV can display line or area shape files but I am not sure if it can display point shape files.

It’s a good idea to use File/Save As to resave your IDV map images now.

To be turned in: A map display showing the San Marcos basin overlying a short wave radiation flux map.

6.  Data Probe of the San Marcos Basin

Now we are going to set up a Data Probe, which is a query tool to get values from the display.  As shown below, open up a new display of the 3 hr fcst surface downward radiation flux 2D Grid.

Now, instead of selecting a map display, select the Data Probe

You’ll see a window that says Probe Control, and a little blue box in the map display.  (you might have to zoom out to find the little blue box).


As you move the little blue box around, you’ll see the values in the Probe Display change.   Fix the probe location at 29.9°N and 97.9°W.  This is just where the outlet of the San Marcos River at San Marcos occurs by IH-35 (at the campus of Texas State University).  

Cycle through the map displays and you’ll see the values under the probe change:

If you right click in the Table of the Probe, use the Edit option in the Probe Table, you can add additional parameters to be measured at the probe, and you can also delete parameters. It seems that the probe can handle up to 6 parameters in its display.  Since our problem has seven fields that we want to examine, you can do this in two passes, adding or deleting fields from the probe table as required.

Here is a graph showing the various energy balance components through the day for July, 2003.

Here is a plot of daily average values of the flux components.  The upward longwave and shortwave components have been made negative in this plot to indicate that they are energy losses from the earth’s surface.   Net radiation = DownSW + DownLW – UpLong – UpShort.   This net radiation is consumed by ground heat flux (G), latent heat flux (L) and sensible heat flux (S).   The balance is the sum of the net radiation and G + L + S.  It should theoretically go to 0.

To be turned in:  Make a table showing the Downward Short Wave Radiation values for 29.9°N and 97.9°W for each three hour interval during the day in July.   Make a similar listing for the values of

1. Downward Longwave Radiation Flux
2. Downward Shortwave Radiation Flux
3. Ground Heat Flux
4. Latent Heat Flux
5. Sensible Heat Flux
6. Upward Long Wave Radiation Flux
7. Upward Short Wave Radiation Flux

Make graphs showing data series 1-7as a function of time of the day.

What is average July evaporation in mm/day at this location?

Use the NARR to make another energy balance study of your own devising.   Compare the values you obtain for the period you choose with the ones that you’ve obtained above for July 2003.

Ok, you’re done!