Meteorology 302.01, Spring 2004
Class Notes for May 3, 2004

 

Angela Blank and Larry  Sharifdeen

 

Assignments:

Vasquez: Chapter 3, pp. 50-51, 54-56,58-61 67-77; Chapter 4, 78-86, 91-95; Chapter 5, 118-124; 170-172, 184-186; Appendices, browse, 271-274

 

Housekeeping:

v    Brief discussion of midterm 2

v    ÒClassic LightningÓ:  cloud to ground, cloud to cloud, and within the cloud.

Lightning:

 

ÒSpecial LightningÓ

We discussed sheet lightning, heat lightning and ball lightning. 

  1. Sheet lightning is lightning which illuminates the cloud between the observer and the lightning stroke.  The lightning stroke is not visible to the observer; thus, the observer only sees the light emanating from behind the cloud.
  2. Heat lightning is visible at night when there are clear skies. The originating cumulonimbus, however, is not visible.
  3. Ball lightning is composed of circular electrical discharges which are about 10 meters in diameter.  They are not will understood.

 

Pictures:

 

We observed some pictures of various clouds:  cumulus clouds, cumulus congestus clouds and cumulonimbus clouds. 

 

We saw that if the cumulus congestus cloud was pushed to one side at the top, then there was a strong jet streme present that was shifting the cloud.

 

We also observed vertical wind sheer.  The picture showed the hail to be present only to the right side of the storm.

 

Lightning Safety:

 

If lightning is near, take cover, go to a low spot and make yourself small.  If you are indoors, stay away from the windows because the thunder can break the windows.  Although we do not know the reason, cars are places of safety.

 

Chaos Theory:

 

We discussed the discovery of chaos theory.  In 1960, Edward Lorenz was working on weather prediction. He used a computer to model the weather so that it would predict what the weather would be, such as how the pressure would vary at a spot. The pressures were measured to six decimal places.  A year later, he tried to experiment with only three decimal places.  He found that, the longer the time period, the more inaccurate was the programÕs prediction with the original prediction.  

 

Ensemble Forecasting:

 

We then went over the definition of ensemble forecasting: Putting a purposeful error into the observations to see what will happen. It is a way of evaluating the stability and the "believability" of a forecast. The basis for this approach is from Lorenz's original experiments on the impact of chaos on weather prediction.