The Fujita Scale

A well-known meteorologist and tornado research scientist, Dr. T. Fujita of the University of Chicago, has formulated a scale of tornado intensity based on observation of the effects of hundreds of the storms. The wind speeds range from less than hurricane force to more than 260 kt (300 mi h). There are six categories, designated F0 through F5, in order of increasing violence. The Fujita tornado intensity scale, as it is called, is outlined in Table 5-1. In a tornado with winds that rotate...

Convergence Of The Easterlies

Near the equator, the belts of tropical easterly winds meet. This is the intertropical convergence zone ITCZ , which was introduced in Chapter 2. It is a region of low pressure and light winds. Thundershowers often form in this zone. In ancient times, this region was called the doldrums, because sailing ships passing through it on their way from the northern hemisphere to the southern, or from the southern hemisphere to the northern, were often becalmed for lack of wind. In the Atlantic, the...

Birds Roost Before A Storm

The notion that birds roost sit around and don't fly much when a storm is approaching has a sound basis, assuming birds can sense weather changes. During times of adverse atmospheric conditions, the informed small-plane pilot stays on the ground. Before a storm comes in from the sea, small craft remain in port. Do birds really have a built-in sense of the weather to come Many people, especially rural folks, will tell you they do. If they do, then they apparently heed it. The next time a big...

The Effects Of Human Activity

During the 20th century, the 1930s drought was much worse than any of the others. The reason is not certain, but perhaps improper farming techniques had something to do with it. People found out that New England farming methods did not work in the Great Plains. When the soil out west was plowed, it dried out during the summer months, and the almost constant winds blew it away. After the 1930s, trees were planted as windbreaks, and much of the land was irrigated. Droughts are correlated with...

Are Droughts Cyclic

Temporary droughts, such as the one that took place during the 1930s, occur when the high-pressure belt is closer to the pole than normal. The conditions that produce a temporary drought are the same as those that cause a heat wave a persistent ridge in the jet stream over a continent. Then, in the northern hemisphere, the desert belts shift or expand northward. Summer rainfall decreases while the temperature increases. There were other droughts during the 20th century besides the dust bowl of...

Waves Depressions And Storms

All hurricanes begin as tropical waves. These are first observed as irregularities, or bumps, in the tropical isobars Fig. 6-2 . Showers and thunderstorms develop on the eastern, or trailing, side of the disturbance. Tropical waves, also called easterly waves, are common during the summer months, and they usually move from east to west without intensifying. But when conditions are favorable for intensification, an easterly wave can develop a cyclonic circulation. When some of the isobars become...

Air Pollution Meteorology Quiz

You may refer to the text in this chapter. A good score is 8 correct. Answers are in the back of the book. 1. Silver iodide is a chemical that is believed to increase the likelihood of a rain or snow, when it is scattered in clouds. b global warming, if it accumulates in the atmosphere. c global cooling, if it accumulated in the oceans. d the formation of amino acids in bodies of water. 2. Which of the following statements a , b , or c , if any, is false a The earth,...

Symbols In General

Air Mass Symbols

The temperature data on a weather map gives an indication of the locations of fronts, where air masses having different characteristics come together. Most severe weather occurs near fronts. The isobars are kinked along the line of an intense or fast-moving front. Stormy weather tends to occur near these zones. Weather fronts are plotted as lines with bumps or barbs that indicate the type of front and the direction of movement. There are four major types of fronts. In a cold front, a cold air...

Gases In Outer Space

Outer space was once believed to be a perfect vacuum. But this is not the case. There is plenty of gaseous matter out there, and much of it is hydrogen and helium. There are also trace amounts of heavier gases, and plenty of solid rocks and ice chunks as well. All the atoms in outer space interact gravitationally with all the others. The motion of atoms in outer space is almost random, but not quite. The slightest perturbation in the randomness of the motion gives gravitation a chance to cause...

Factors That Affect Hurricane Tracks

Upon analysis of past hurricane paths and their relationship to the surrounding weather systems, a correlation can be found between hurricane tracks and the conditions in the temperate zone. When a large area of low pressure exists to the west of a hurricane, the storm will at first be drawn toward this low-pressure region. Then the hurricane will be steered around the eastern edge of the low, where the winds come from the south. The hurricane moves northward into the belt of prevailing...

Synoptic Forecasting

High And Low Pressure Systems Maps

The term synoptic means generalized, or taking a view of the whole. Synoptic weather forecasting is done by assembling weather maps of large regions from observed and reported data at numerous stations station models . The defining tool of synoptic forecasting is the weather map. Synoptic forecasting evolved before computers were available to analyze weather data in high detail. A meteorologist might look at a sequence of weather maps showing conditions in the United States at intervals of a...

The Atmospheric Capacitor

Capacitor World From The Ionosphere

The earth is a fairly good conductor of electricity. So is the upper part of the atmosphere known as the ionosphere. The air between these two conducting regions, in the troposphere where most weather occurs and in the stratosphere, is a poor conductor of electric current. When a poor conductor is sandwiched in between two layers having better conductivity, the result is a capacitor. A capacitor has the ability to store an electrostatic charge. This produces a potential difference voltage...

Tornadoes And Microbursts

The wind damage from a hurricane results mainly from the prolonged, violent blow in the eyewall. Few hurricanes retain deadly wind speeds farther than about 160 km 100 mi inland, although this depends to a large extent on the terrain, and considerable damage can still result from sustained winds of 50 to 60 kt about 60 to 70 mi h . Hurricanes can produce tornadoes, however, and these have higher wind speeds than those in the general circulation of the eyewall. Tornadoes are most frequently...

Thermal Inversion Cause

Thermal Inversion Diagram

In stable air, the temperature decreases at a fairly uniform rate as altitude increases. This holds true for several kilometers upward. Frontal systems upset the uniformity, and this is partly responsible for the formation of rain clouds. In the vicinity of a frontal system, the temperature drops at first with increasing altitude, but when the boundary between air masses is reached, the temperature abruptly increases. As the altitude increases further, the normal pattern resumes. Fig. 4-2 is a...

The Station Model

Today, every city has a weather station that is linked by wire, fiberoptic cable, terrestrial radio, and satellite systems to a central office. The meteorologist in Rochester, Minnesota, can find out in a matter of seconds what happening in Eureka, California. The data from a particular place includes temperature, dew- point, extent and type of cloud cover, type of precipitation if any , wind direction, wind speed, and barometric pressure. All of this information is fed into a computer, and the...

Meanders In The Jet Stream

The jet stream flows in an irregular path, not straight around the world at one latitude. An experiment can be conducted to demonstrate this effect on a small scale, using a rotating pan, ice, water, and a heating element. The pan is filled with water of a moderate temperature. A container of ice water is placed at the center of the pan, and the heating element is placed under the periphery of the pan, all the way around Fig. 2-5 . This sets up a battle between cold water and hot water....

When Air Is Squeezed And Stretched

Convergence And Divergence Air

The jet stream varies in width and speed, as well as in direction. These variations cause air to be pushed together, or compressed, in some places causing an increase in pressure. In other places, the air is pulled apart, and the pressure goes down. Either of these situations can result from changes in the width of the jet stream, its speed, or both. When air is pushed together, it is said to be converging, and when it is pulled apart, it is said to be diverging. Fig. 2-6 illustrates...