Published Tuesday, January 28, 2003 in the San Jose Mercury NewsWeather Corner
Even when the economy turns south, dot-coms go bust and the stock market struggles, there is always weather -- and a need for people who understand it. The latest outlook from the Department of Labor indicates that the hiring of meteorologists and other atmospheric scientists is expected to increase 10 to 20 percent during the next decade.
Of the nearly 7,000 meteorologists nationwide, the federal government employs about 40 percent. However, the National Weather Service, the largest government employer of meteorologists with a degree, has recently finished a massive restructuring that doesn't leave the agency with many job openings.
Consequently, most of the projected employment is expected in the private sector. In the Bay Area, there are about a dozen meteorological firms and government agencies that employ, collectively, about 100 meteorologists. People in some weather-related jobs, such as media weathercasters, don't count toward that total if they don't have a degree in meteorology.
The working conditions for most meteorologists are very good -- most have increased computer capability and clean (but not always tidy!) workplaces. Probably the biggest negative in a weather forecaster's work life is the requirement to work nights, weekends and holidays. Many good meteorologists quit the profession because of such work shifts.
When it comes to the weather, though, serious learning is required to get it right. In the next Weather Corner, I'll look at what it takes to get a degree in meteorology.
Q What's the explanation for white frost forming on auto tops, etc., when the air temperature is still 3 or more degrees above freezing? Bob Hochmuth - San Jose
A Frost forms in a process called deposition, when water vapor goes directly to its frozen state and bypasses the liquid phase. This can occur even when the air temperature is above 32 degrees if the object that the moist air comes in contact with is less than 32 degrees. When skies are clear, objects like leaves, roofs and cars radiate heat back out to space and cool faster than the air. There can be as much as a 6-degree difference between the temperature of the air and some of these objects. Thus, it's possible to see frost when the air temperature is as high as 38 degrees.
Q How about discussing rainbows visible at night? I remember seeing a complete circle around the moon while serving with the Marine Corps in the Pacific during World War II. Lou Gado - Los Altos
A The ring of light you are referring to can occur around either the sun or moon and is called a ``halo.'' It is formed when sunlight or moonlight passes through high, thin cirrus clouds which are made up of tiny ice crystals. The light is refracted through the crystals, forming a 22-degree halo, instead of the 42-degree arc of a rainbow formed by raindrops.
A rarer phenomenon is a moonbow, which is a nighttime version of a rainbow. The light from the moon is refracted and reflected through raindrops, but because the intensity of moonlight is less, the colors are less vibrant and moonbows have a pale whitish appearance.
Q What is the relationship between aircraft noise and temperature inversions, in terms of aircraft noise levels? David Ong - San Francisco
A The propagation of aircraft noise is dependent on many factors, including distance, wind, humidity and temperature. The distance part is straightforward -- as sound energy spreads out over an increasingly larger area, the amount of noise decreases. Additionally, the noise from low-level aircraft operations are affected by absorption and deflection from the Earth's surface as well as by intervening objects like hills and buildings.
And, as you suggest, atmospheric temperature gradients also affect aircraft noise propagation. When there is not an inversion and the air temperature slowly decreases with increasing altitude, aircraft noise is, for the most part, deflected upward and away from most ground-based listeners.
However, when there is a temperature inversion with a layer of cool air trapped near the surface, the reverse situation is true and aircraft noise tends to be deflected downward, creating increased sound levels over a longer distance.
Water vapor in the atmosphere is also relatively effective at absorbing noise. On many of the nights with an inversion layer, the high humidities will mitigate the noise levels.
Q While I was living in Arcata, I remember a storm in November 1981 that registered a very low pressure of 28.96 inches or 980 millibars. What is the lowest recorded barometric pressure in the Bay Area? Ray Dawley - Redwood City
A You're probably not old enough to remember, but Arcata had an even lower pressure in February 1915, when the pressure fell to 28.93 inches of mercury. The record-low pressure in San Francisco is even lower, with a 28.85 recorded in January 1916.
Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o WeatherCorner, 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, e-mail them to email@example.com or fill out a form online at http://ggweather.com/questions.htm. Please indicate in your e-mail what city you live in.