Instructions for using the java sounding applet with interactive parcel trajectories

The sounding consists of a Skew-T plot, a hodograph, and a wind speed plot. The following thermodynamic indices are also shown, if available: A parcel may be specified by clicking with the mouse at any point. The parcel will ascend from that point (using the environmental dewpoint at that pressure), and regions of CAPE and CIn will be indicated. The Lifted Condensation Level (cloud base) for the parcel is indicated by a short horizontal black line on the parcel trajectory. Right-clicking with the mouse will bring up a selection window that will allow you to select the initial parcel dewpoint, temperature, and pressure. Click on a sounding's button to remove the parcel trajectory. Thanks to Tom Whittaker of the University of Wisconsin for providing the core of the code that performs this task.

(Against Tom's advice, and to facilitate stability calculations using ACARS soundings that often lack humidity data, iCAPE and iCIn are calculated using the temperature difference between the parcel and the sounding, rather than the virtual temperture difference. According to Doswell and Rasumssen (1994, Weather and Forecasting, 9, pp 625-629), this may cause errors > 30% for values of CAPE below 500 J/Kg and similar errors in CIn, but smaller error for larger values.)

The hodograph shows wind speed in kts, and height in km.

The sounding has two default altitude ranges, one extending up to 150 mb and the other to 10 mb. Each of these ranges can be zoomed by dragging the mouse diagonally across the portion of the Skew-T plot desired. Unzoom by clicking a 'scale' button. (To drag, hold the mouse button down while moving the mouse. When you release the mouse button, the zoomed region will fill the plot.) (The zoomed region will have the same aspect ratio as the main plot, so the red rectangle that appears may not follow the mouse quite the way you think it should.)

Other functions are as follows:

Move the mouse along the sounding to see the following printed at the level of the mouse point (from left to right):

In addition, the temperature and pressure for the cursor point is indicated below the cursor.

Click on the Load Sounding(s) button to pop up the choose sounding window. In this window you can

Once a sounding is loaded, you can use its button to (re)display it.

The sounding information shown on each button consists of the site name, and a code:

Printing the sounding plot. Because this is a java applet, you may or may not be able to print it. It depends on your browser setup, and many browsers do not print java applets. In this case, we recommend that you use a screen capture utility. We have used the following capture utilities: on Unix, xview; and on Windows95, HyperSnap.

This code is available as open source software. You may receive a copy if you agree to abide by FSL's License/Disclaimer.

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Prepared by Bill Moninger,
Last modified: Fri Mar 19 16:09:11 MST 2004