AOS 452 Lab 7: GARP (GEMPAK Analysis and Rendering Program)

1 AOS 452 Lab 7: GARP (GEMPAK Analysis and Rendering Program) (October 5, 2006)

Tip of the Day: Printing complex GEMPAK PostScript files can take a while. Use the lpq program to check on the status of your print job. The –P flag tells the program which printer to check, so, for example, type lpq –P gpend to check the printer in the Synoptic Lab, or type lpq –P synoptic to check the printer in Room 1443 (the old Synoptic Lab).

INTRODUCTION

GEMPAK will be the main tool you use for data analysis in your group and individual case studies. Today, however, we will explore a more user-friendly program that combines many of the GEMPAK programs into one package–GARP. GARP can be thought of as a “point-and-click” version of GEMPAK that presents a graphical user interface (GUI) instead of a list of parameters in individual programs. You may be asking yourself, “Why are we using the more complicated GEMPAK programs when GARP is available?” In short, GARP is much more restrictive in its manipulation and display of data than the GEMPAK programs. It is also a little slow and buggy. Finally, a new program, called IDV, is currently being developed to supercede both GARP and Vis5D (to be explored in future labs), so GARP is a bit of a lame duck. I will warn you right now: Do not use GARP for any graphics you will present in your case studies! GARP will be most useful in taking a first glance at data sets, getting a quick idea of the current weather, creating overlays with satellite or radar data for map discussions, and nowcasting/storm chasing base support.

THE MAIN GARP CONTROLS

To begin the program, simply type garp at the Unix prompt. A display window should appear that fills the screen. At the top of the window is the main menu bar. A brief description of each selection is given below:

File: The only two options in this menu are “Save” and “Quit”. The process of saving images will be explained near the end of this lab. View: Contains menu items for selecting particular data types. The menu options essentially are the same as options available through the data type icons (the data type icons will be explained shortly). Area: Contains pre-defined geographic regions that will be drawn in plan view displays Time: Adjusts time-related parameters Options: A menu with a smorgasbord of features available in GARP Help: Help menu

Below the main menu bar, there are 10 data type icons. These icons are described below:

ICON 1 View satellite and radar imagery ICON 2 View surface data plotted on a standard surface chart (similar to sfmap) 2

ICON 3 View wind profiler data (may not be currently available) ICON 4 View upper air observational data plotted on a standard plan view upper-air chart or a thermodynamic diagram (similar to snmap and snprof) ICON 5 View horizontal plots of gridded (model) data sets (gdcntr, gdwind, or gdplot) ICON 6 View vertical cross-sections using gridded (model) data (similar to gdcross) ICON 7 View time-height sections ICON 8 View vertical profile (sounding) plots from gridded (model) data (similar to gdprof) ICON 9 Clear the graphics window (without clearing the map background) ICON 10 Resets the graphics screen, so it appears as though you first began running GARP

In this lab, you will go through a few small exercises to familiarize yourself with a few of GARP's capabilities. You can easily learn many of the other capabilities in GARP with a little experimenting.

MODEL PLAN PLOTS

To start things out, we are going to select a graphics area for a future plot. Drag the arrow to the AREA menu on the main menu bar. Click on AREA and select CONUS. A map of the continental United States should appear in the display window.

Now we are ready to choose a variable to plot. Click on the icon for horizontal plots using gridded data (ICON 5) with the left mouse button. A window with the title “Model Plan View” will appear.

The next step is to select a model. Click and hold down the left mouse button on the upper-left box where a model name (probably GFS thinned) is shown. A pull-down menu will appear with different models listed. Select the Eta 211 model. (GARP hasn't been updated to reflect the name change yet.)

After possibly many seconds, you should see a list of date/time stamps in the column with the header “Available Times” (or Date/Time). The date/time stamps are given in the following format:

yyyymmdd/ttttFTTT yyyy = the four-digit year identifier mm = the two-digit month identifier dd = the two-digit day identifier tttt = the hour of the model run (1200 = 1200 UTC, 0000 = 0000 UTC, etc.) F = stands for forecast time TTT = forecast hour (024 = 24-hour forecast time)

Note that the yyyymmdd/tttt tells the user from which model run the data are derived, or, in other words, what day and time the model was initialized. The FTTT tells the user the forecast hour from this model run. For example, 20061005/1200F012 would be the 12-hour forecast from the 1200 UTC 5 October 2006 model run, valid at 0000 UTC 6 October 2006. As such, not all the times listed correspond to the same model run. Generally, you will want to use the most recent data available (found at the bottom of the list).

Let’s try plotting geopotential height and absolute vorticity at 500 hPa using the 24-hour forecast from the 1200 UTC 5 October 2006 Eta/NAM model run. Be sure to select the appropriate time, pressure coordinate, level, correct functions, etc. You can always adjust the contour interval and 3 contour properties of the variables being plotted by selecting more on the lower right of the Model Plan View box. Once you get the heights to plot overlay the absolute vorticity. See if you can get the absolute vorticity to appear with color filling instead of contours.

NOTE: In GARP, it is easy to clear a variable that you plotted without clearing the entire screen. Simply go to the bottom of the graphics window and single click the left mouse button on the title of the variable you want taken off the screen. The title text will turn gray. You can bring the variable back up onto the screen with a single click of the left mouse button on the grayed-out title.

FURTHER NOTE: In addition to selecting the already defined variables and functions, one can manually enter a gfunc or gvect in the bottom part of the Model Plan View window.

Click ICON 9 to clear the graphics screen. Your plot should be cleared with only the background map remaining.

LOOPING WITH GARP

In GARP, we can easily loop through a series of images, even with multiple overlays. We will now make a loop of the visible satellite imagery with surface observations overlain. Use the Northeast United States as the map background.

 Click on the satellite and radar icon (ICON 1).  Select GOES-8 (this is actually GOES-12 data), 4 km, and VIS.  Click and hold the left mouse button on 20061005/1315 and drag down to the most recent time. There should be about 7 forecast times highlighted.  Click the “Display and Close” button. You should see a series of satellite images plotted on the screen.  Since we want to display surface observations taken around the same time the satellite pictures were, we should use the “Time Matching” feature of GARP. In the Time menu, select Time Matching, and then select Closest Time Match.  To overlay the surface obs, select ICON 2. Click Multi-color. Notice that the proper times are already selected to match the satellite.  Click on the “Display and Close” button. The surface obs should overlay the satellite imagery.  Two methods can be used to loop through a series of images. You control the loop by clicking on the buttons located to the right of the Speed and Fade slide bars in the top portion of the main display window. The buttons look like the following:

Stepping through the frames one at a time Clicking on the “<” button will bring up the next frame backward in time, while clicking on the “>” icon will bring up the next frame forward in time. 4

Looping through the frames Clicking the “<<” button will loop the frames backward in time, while clicking the “>>” will loop the frames forward in time. Clicking the “<>” button will loop from the beginning frame to the end frame, then loop back to the beginning frame. To stop the loop, click on the button with the square.

DEFINING THE GRAPHICS AREA IN GARP

To begin this lab, you defined a graphics area covering the United States. Experiment with the other graphics areas which are available from the area menu. Also, as in GEMPAK, you can zoom into an area (and redefine the graphics area) by using the mouse. This is similar to the cursor command covered in previous labs. Just create the box as if someone had already typed in the cursor command for you, and GARP will automatically change the graphics area for you.

SAVING PLOTS IN GARP

If you are in a time crunch (and who isn't?) and you want to create simple plots in GARP for your map discussion, you will want to save the output. Once your plot (or loop) is complete, just click on file and select save. Click on apply after creating the filename, and the file will be saved in your own directory.

EXITING GARP

To exit GARP, click on quit from the file menu. It is not necessary to type gpend when exiting GARP.

CREATING AN ANIMATION FROM A GARP LOOP It is not too hard to convert a GARP loop into an FLI animation. Here's how: 0) As an example, create a loop of satellite imagery in GARP. 1) Click save from the file menu, just as if you were saving a plot. This time, though, click the All Frames button. 2) Give your loop a filename, but without the .gif extension. For this example, just type sat. 3) Exit GARP 4) Type ls sat* and notice that GARP automatically numbered your images and supplied the .gif extension. 5) Type file sat01.gif (for this example) and notice the image size. 6) Type ls -1 sat*.gif > sat_list This command lists in one column all files matching sat*.gif, and places the output in a file called sat_list. 7) Type cat sat_list to make sure the appropriate files are in your image list. If not, you'll have to nedit the sat_list file. 8) For the final step, you'll type something like: ppm2fli -N -g 1098x748 –fgiftopnm sat_list sat.fli where 1098x748 should be replaced with the appropriate image size. This runs the FLI conversion program, with -N specifying that xanim will be able to play the loop backwards, -g ###x### specifying the animation size, -fgiftopnm specifying that the original images are GIFs, sat_list specifying the list of images to convert to an animation, and sat.fli specifying the name of the resulting animation.

Now you can type xanim sat.fli & to view your animation.