Instructions for using the java sounding applet with interactive
The sounding consists of a Skew-T plot, a hodograph, and a wind speed
plot. The following thermodynamic indices are also shown, if
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.
- CAPE (Convective Available Potential Energy) in J/Kg
- CIn (Convective inhibition) in J / Kg
- PW (Precipitable water) in Kg/m^2
- Helic (storm-relative helicity) in m^2/s^2
- TT (Total Totals index)
- KI (K index)
- LI (Lifted index)
- SI (Showalter index)
- LCL (Lifted Condensation Level, based on the average
temperature and dewpoint in the lowest 100 mb)
- iCAPE (approximate CAPE based on the
lifting of a parcel that you input)
- iCIn (approximateCIn based on the
lifting of a parcel that you input)
- iLCL (LCL based on the lifting of a parcel that you input,
using the initial temperature and dewpoint of the parcel)
(Against Tom's advice, and to facilitate
stability calculations using ACARS soundings that often lack humidity
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
In addition, the temperature and pressure for the cursor point is
indicated below the cursor.
- The pressure in mb, and the pressure altitude in km and feet.
(For ACARS data, the time, bearing and range from the airport are
- The dewpoint in Celsius (and also Farenheit below 750 mb).
- The temperature in Celsius (and also Farenheit below 750 mb).
- The wind direction and speed in knots.
- A highlighted wind barb.
- A highlighted portion of the wind speed curve.
- A highlighted portion of the hodograph
Click on the Load Sounding(s) button to pop up the
choose sounding window. In this window you
- Enter a 3- or 4-letter
ACARS-airports site name. (Contact Bill
Moninger if your favorite METAR site is missing.)
- OR, enter a latitude and longitude (in decimal,
with west and south being negative), separated by a comma.
- Enter a starting valid time by choosing a year, month, day, and
- Enter the number of hours of soundings you would like to
display. MAPS (RUC) soundings are generally available
for the past 16 hours, and for intermittent hours up to 36 hours
into the future.
Remember that RAOBs are only available at 0
UTC and 12 UTC.
- Click on a data source,
ACARS. (ACARS data are restricted to
certain users, per FSL's agreement with the airlines that provide
Soundings will appear one after another on the
plot as soon as they're ready, and a button with
each sounding's information will appear below the plot.
Once a sounding is loaded, you can use its button to (re)display
- Click on a button to clear the display, and
display one sounding.
It generally takes less than a second for an already-loaded
sounding to reappear.
- Shift-click one or more buttons to
add additional soundings
to the plot. (Shift-click means hold down the shift key while
clicking the mouse button.)
- Control-click a sounding's button to remove
the sounding and its button.
The sounding information shown on each button consists of the site
name, and a code:
R indicates a RAOB sounding
P indicates a Profiler sounding
A indicates a sounding from a MAPS analysis
a indicates a sounding from a RUC-2 analysis
Fn indicates a sounding from a MAPS n-hour
fn indicates a sounding from a RUC-2 n-hour
- For instance "DEN(F9)" indicates that the
sounding data are from a MAPS forecast based on an analysis from 9 hours
before the indicated valid time.
Dn indicate ACARS ascent or
descent soundings, respectively.
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 |
Prepared by Bill Moninger,
Last modified: Fri Mar 19 16:09:11 MST 2004