Meteorology 356

Class Notes

11/22/04

Alek Butler

Readings

· No new readings

Assignments

· Midterm November 24

· Bring Scantron Form #882 and a number two pencil

· Midterm in 50 multiple-choice questions. Major question include:

1. Mediterranean Climate

2. Thermal and Dynamic pressure systems

3. Rainfall variability

4. More weather map interpretations

5. Diablo winds

6. Tule fog

House Keeping

• Study for the midterm
• Finish reading assignments if behind
• Have a good Thanksgiving

Global Warming in California

• Remember that all these charts can be tricky and lead to false conclusions
• First looked at a graph of San Francisco temperatures over a few years
1. Looks like the temperature has been increasing

• Second looked at a graph of Sacramento’s temperature trends
1. It also shows temperatures increasing
• If this temperature increase is global warming it should be uniform around the world

1. However, Chico’s temperature charts don’t show an increase in temperature

2. This exercise was to show how charts like these can give false correlations

• Guesses why these cities show an temperature increase over the years
1. As fault and cement in big cities absorb more heat
2. Normal swings of climate
3. Can’t come up with a solid conclusion if there not enough years in the statistical charts
• Conclusion: be careful how you use the word correlation

1. EX: Some try to draw a correlation between precipitation and sunspots (charts on class website). However, over a longer amount of time with more statistical information it is seen that any correlations were just chance

Concept of Return Period

• Use with caution
• Are suppose to use 30 years of statistical information
• Even if a 10,000 year event occurs doesn’t mean it will only happen once every once every 10,000 years. It only mean it has a one in 10,000 chance of occurring in a given year

Looking at the 30 year mean rainfall chart of San Francisco (class website)

• Shows rainfall averages starting high, than about twenty five years of less rainfall, and lastly the rainfall increasing again
• Good example of natural climate swings
• Therefore, maybe over the past few years with SF experiencing more rainfall this new event is not a climatic change, but just going back to what it was thirty years ago. This is like a natural weather variation
• The coefficient of variability also suggest the same thing

CAPE (refer to class website)

· Although, dew point infers where thunderstorms can occur CAPE takes in everything that can produce thunderstorms into account

· Rule of thumb/ CAPE measures instability

1. The atmosphere destabilizes (becomes more unstable)

· The higher the surface dew point temperatures (this is the largest effect)

· The colder the temperatures are aloft

· The warmer the temperatures are at the ground

Another Way of Warming Air

• Latent Heating (class website): Provides a source of heating to allow the temperatures to be higher
• Ex. drawing on board and in reader

Stages in the Development of Common Thunderstorms

• In order for air to rise the ground needs to be warmer than the air around it
• The first two stages Cumulus and Cumulus Congestus were discussed last class session (class website)
• The third stage is Cumulonimbus Stage (class website)

1. Usually develops around 2 through 3 in the afternoon in the four corners region or the Sierras

2. Updrafts of 30-40 even 50 mph

3. The spread out top is frozen (the freezing level)

· Spreads out evenly (anvil phase)

4. Hail is in the freezing level

• Hail
1. Made in the freezing level
2. The stronger the updrafts the more transitions the hail can make through the freezing level, and the more transitions the hail makes the larger it becomes
3. You can cut the a hail stone in half and see the ring of how many times it has been through the freezing level, and determine how strong the updrafts were
• Down Drafts: The winds with the hail and rain rush down to the ground

Lightening (definition on website)

• The hypothesis of what makes lightening: Hail in the cloud strikes each other knocking off electrons. This creates a negative charge in the freezing level of the cloud. This creates an unequal charge difference. Nature doesn’t like this so it releases an electrical charge (lightening) to equal this difference.
• Three different kinds of lightening strikes

1. Cloud-to-ground (most dangerous)

2. Cloud-to-cloud

3. Within-the-cloud

· Sheet lightening: Lightening on the other side of the cloud that blocks the seeing the lightening and just lightens up the sky

Thunder (website)

• Peal and clap also on the class website