Meteorology 302.01,
Spring 2004
Class Notes for March 29, 2004
Trevor Harrison
Assignments
- Writing Assignment II Distribution: Postponed Until 7 April
- Vasquez: Chapter 2, Browse, 20-46; Read p. 47; Chapter 3, pp. 48-50; Chapter 4, 103-110; Appendices, p. 270; p. 287.
- Nova: Watch Tuesday, March 30 @ 8pm on PBS… OR
- National Geographic, April 2004: Read article on Tornado Chasing.
(There will be questions on Midterm II about how the profiled meteorologists used the scientific method)
- National Geographic Website: Watch 8 minute online presentation.
- Homework #2: Due Monday April 5, 2004.
Housekeeping
- Writing Assignment #1 will be returned on Friday, April 2.
- We reviewed the introduction section from Examples of Good Writing. We will review the other sections at a later date.
During the latter half of our spring break, a meteorological anomaly formed off the coast of Brazil. It was by most counts the first ever recorded hurricane in the South Atlantic. Because of this, no name was given, or ready to be assigned, but the Brazilians have dubbed it Catarina. Satellite images clearly show what looks to be a hurricane with a visible eye (Image 1, Image 2, Image 3). There is a connection we have not yet discussed between the formation of an eye of a storm and wind speeds. Preliminary reports suggested it was a category 1 hurricane on the Saffir-Simpson Scale. However, some controversy has emerged. Brazil, unlike the US National Hurricane Center, does not have aircraft available to fly through such storms to measure its strength. As a result, Brazil has refused to classify Catarina as a hurricane. Instead, the Brazilian Weather Service has classified it as an extratropical wave cyclone. All of their forecasting was biased by their preconceived notion that this was an extratropical storm. The Sun Sentinal and CNN have both run stories concerning this weather anomaly, and possible explanations for why the Brazilian government refused to classify it as a hurricane. Caveat - there is always information missing from media articles, possible misquotes, or the journalist was unclear of the topic. Developing…
Divergence – How Nature Creates Low Pressure Areas on the Ground
Previously, we briefly discussed Divergence. Divergence is defined as the motions that result in neighboring air parcels at a given level “spreading” apart. An understanding of divergence will explain how nature creates areas of low pressure. In today’s class we looked at Part II of Conceptual Divergence. This diagram relies on two rules of thumb to explain divergence:
1. Nature Does Not Like Vacuums Part I: At a given level, air tends to move horizontally from higher values of pressure to lower values of pressure (Note: due to Coriolis Effect the air really "spirals" from higher values of pressure to lower values of pressure).
2. Nature Does Not Like Vacuums Part II: Divergence in the upper troposphere is associated with rising air from beneath and convergence in the upper troposphere is associated with sinking air beneath.
By removing bricks at the tops of air parcels, areas of low pressure are formed on the surface, called divergence aloft. An imbalance is formed, and nature does not like vacuums, so equilibrium in pressure is sought. Air rushes in at the bottom of the parcel, but is retarded by surface friction. More air goes out of the top than enters in the bottom. Once this air is in the column, it too rises, and is cooled, and if water is present clouds and precipitation commonly form.
Why or how divergence occurs is a more difficult question. Thankfully, there are only two ways; one way will help us understand hurricanes and the other will help us understand wave cyclones. These 2 ways account for 100% of the formations of surface highs and lows. All four of the rules of thumb are used to explain these two ways.
Warm Core Lows
For this section we only needed to follow along. This portion of the lecture can be heard in Real Audio by clicking here. To play it, you will need the Real Audio Player and a soundcard in your computer. (The file is 1.89MB and the sound quality is not the best.) The diagrams used during this topic discussion can be found in these links:
Warm Core Lows: Crosssections I (with supporting Weather Maps For Case A and B) and II (with supporting Weather Maps For Cases C and D). This is conceptual information that helps to understand The Main Reasons for Development of Surface Pressure Systems. We are to read through the top half of this handout and will discuss it in more detail next time.
