the WEATHER CORNER

Promoting weather education

BY JAN NULL
Special to the Mercury News 

Meteorology appears to be a forgotten science in California's schools, even though it is the one science that everyone uses everyday. Every aspect of our lives, from how we dress for the day to the ongoing energy crisis, is affected by weather. That's why television serves up the Weather Channel, not the Chemistry Channel or the Physics Channel.

This shortcoming in most students' science schooling starts with the California Department of Education's skimpy study requirements for meteorology. State science guidelines for public school students call only for minimal weather and climate study in the first and fifth grades, with one more course of study in high school.

For those looking to supplement this meager curriculum, I have assembled Weather 101, an online resource for teachers, students, and anyone interested in meteorology. It is a work in progress, and can be found on the Web at http://ggweather.com/101.htm .

The Weather Corner also tries to help along meteorology studies by answering questions from students. This week's queries come from Ms. Genevieve Deppong's seventh-grade earth science class at St. Raymond's School in Menlo Park.

Q. Why do tornadoes happen only in the middle of the United States? Mike - Redwood City

A.  This is a common misconception. Actually, tornadoes have occurred in every state, and even occasionally here in the Bay Area. However, the biggest, baddest tornadoes are usually in the Midwest, where cool air from Canada clashes with warm moist air from the Gulf of Mexico to form twisters.

Q.  What is the impact of air pollution on weather patterns? Rudy - Menlo Park

A.  One of the most researched effects is the way that air pollution can account for increased rainfall. This happens when tiny particles of pollution act as condensation nuclei, allowing what would normally be small droplets of water to grow bigger. This effect has been noted in areas downstream from large factories that emit large plumes of particles and exhaust.

Q.  Why does lightning travel up instead of down? Spencer - Menlo Park

A.  Actually, lightning travels up and down. Usually, the lower portion of a thunderstorm develops a strong negative charge and an initial discharge, called a ``stepped leader.'' This electrical discharge, moving about 240 miles per second, reaches from cloud to ground. When it nears the ground, it draws a ``streamer,'' or line of positive charges, upward to meet it. When they meet, an electrical connection is completed between the cloud and the ground, and these ionized air molecules become the
path of the main bolt of lightning.

Then comes the real drama of lightning -- the color and noise. As negative charges rush toward the ground, they collide with the surrounding air, causing it to glow with a bluish-white color. In the meantime, the bright bolt of positively charged lightning moves from the ground upward at 61,000 miles per second. This glowing flash moving from ground to cloud is called the return stroke. This super-heats the air, which expands explosively outward, producing the shock wave we hear
as thunder. 

Q.  Do trees affect the weather, and if they do, what effects do they have? Molly - Portola Valley

A.  Trees can and do affect the weather, both on a local and global basis.  An area with many trees will tend to be cooler than surrounding areas that have lots of buildings and concrete. This is caused by the shade that trees provide and the cooling caused by the water that evaporates from them. Trees are also planted as windbreaks.

On a global scale, trees are an important factor in the conversion of atmospheric carbon dioxide to oxygen. The increase in carbon dioxide contributes to global warming, and fewer trees mean more carbon dioxide in our atmosphere.

Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o Weather Corner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. You also telephone and fax questions at (510) 657-2246 or e-mail them to (weathercorner@ ggweather.com).