Diego Vallejo

Metrology 302.01

Class notes for 4-21-04

We began class by reviewing instability. Instability was defined as the phenomenon of air parcels becoming warmer than other air parcels surrounding them and subsequently becoming less dense. This difference in density causes the less dense air to rise or be more susceptible than the surrounding air to divergence. The example was given of a cork in a swimming pool; the cork rises to the top when released because its density is less than waters. Apparently instability is a spontaneous event which ties into the dew point temperature; the higher the dew point, the more latent heat is released upon rising, causing wetter air parcels to become unstable and thus less dense.

The ability of air to become unstable has a direct way of measurement, known as CAPE. CAPE measures the warmth of air parcels in comparison to the air surrounding them at a given elevation. The opposite of this is known as CIN, which measures the ability of air to become stable; CIN measures the coldness of air parcels in comparison with the air surrounding them. This is the class website link to CAPE/CIN: http://tornado.sfsu.edu/geosciences/classes/m302/CAPE_DewPts/CAPE_CIN.jpg

These two concepts used in an example of a wave cyclone over Texas. As air would be pulled into the cyclone from the south, some air would be pulled from northern Mexico, while other air would be pulled from the Gulf of Mexico. This would cause a dry line to form in the middle of Texas, with point A on the dry side and point B on the wet side. The air on either side of the dry line could be the same temperature, 59 degrees; however, because they are on opposing sides of a dry line, dew point temperature at A would be 5 degrees while the dew point at B would be 59 degrees. As the air in both of the points begins to rise to 1000 ft because of divergence, the air at point B would be cooled to 56 degrees due to latent heat release, while the air at point A would be cooled to 53 degrees. This difference in temperature would cause the air at point A to sink while the air at point B would continue to rise. This is how instability works.