WEATHER CORNER

BY JAN NULL
Special to the Mercury News

During a recent Meet the Meteorologists forum at the San Jose Mercury News, the readers who participated asked a number of questions about the weather and related subjects. Here are some.

Q. What is the all-time high temperature in San Jose? I remember it getting to 114 in 1972, but this last June 14 they said it was the highest at 109. What's the real deal?

A. A search of the 1972 weather archives does indeed show a very hot period that included the previous all-time official high for San Jose when the mercury reached 108 on July 14. Lots of other spots exceeded 105 that day, including Los Gatos, 113 degrees, Gilroy, 112, and Santa Clara 109. The 114 degrees that you remember may have been from an unofficial site somewhere else.

Q.  Sometimes weather stories and your columns use weather terms I'm not familiar with. Where can I find some weather definitions?

A. I recently put online an updated version of a glossary I originally developed for the local National Weather Service Web site. The update can be found at http://ggweather.com/glossary.htm. I plan to add more entries, so please let me know if there are any words that you would like included.

Q.  Does earthquake weather exist?

A.  No. This is one of the most frequently asked questions. Despite the incredible forces the atmosphere has upon Earth's surface, these effects are slight compared to the mass of Earth and are felt only at the surface and in the shallow subsurface. 

Earthquakes originate many miles underground and have been documented in all weather, all climate zones, all seasons and at any hour.

Q. I'm interested in finding a group of people to talk to about the weather, especially severe weather like tornadoes and hurricanes. Stephen Homer - San Jose

A. Everyone talks about the weather, but that usually happens only by the water cooler or in the elevator. I don't know of any organized groups of local enthusiasts. You may find some interesting
Web sites.

The one I visit most frequently, the Usenet Newsgroup: www.sci.geo.meteorology, offers a general discussion of meteorology for amateurs and professionals alike. Common topics
include current and historic weather phenomena, hurricanes and El Niņo. There are also a number of online weather chats. Check out www.weatherpages.com/chat/, http://weather.about.com/newsissues/weather/mpchat.htm and www.weather.com/interactboards/.

You might also look into taking a meteorology course at a local college. A quick survey of fall 2000 class schedules showed meteorology classes at Cabrillo College, College of San Mateo, De
Anza, Diablo Valley College, Cal State University-Hayward, San Jose State University and San Francisco State University. At the community colleges, the meteorology classes are usually listed
under geography, geology or physical science.

Q. I read a nice article in the Mercury News about there being exactly equal amounts of day and night on the equinox. But I then glanced at the sunrise and sunset times on Sept. 22 and noted that
the day and night times were not equal. There was about a seven-minute discrepancy. Checking with my online encyclopedia I found that the article was correct and that the times should be
equal at equinox. What gives?  Bob Loomis - Sunnyvale

A. Rest assured; everything you read is correct. The discrepancy arises from the frame of reference for each event. On the day of an equinox, the geometric center of the sun crosses the equator, and this point is above the horizon for 12 hours everywhere on Earth.

But the sun is not simply a geometric point, it's a disk. Sunrise is calculated when the leading edge of the sun's disk becomes visible on the horizon, and sunset is the instant when the trailing edge of
the disk disappears below the horizon. 

As the edge of the sun appears or disappears, the actual center of the sun's disk is below the horizon. In addition, the refraction or bending of light by the atmosphere causes the sun to appear higher in the sky than it would if Earth had no atmosphere. This combination adds up to several minutes at sunrise and sunset to account for the discrepancy.

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 can telephone questions at (510) 657-2246, fax them to (510) 315-3015 or e-mail them to weathercorner@ggweather.com. Please indicate in your e-mail where you live.