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...

Radar

The term radar is an acronym derived from the words radio detection and ranging. Electromagnetic EM waves, having frequencies in the ultra-high or microwave range, reflect from certain types of objects and particles, including aircraft, missiles, raindrops, ice pellets, and snowflakes. By ascertaining the direction s from which radio signals are returned, and by measuring the time it takes for an EM pulse to travel from the transmitter location to a target and back, it is possible to locate...

The Weather Stick

Long before Europeans came to North America, Native Americans in the region now known as New England discovered that the branches of certain trees bent in one direction in fair weather, and in the opposite direction in foul weather. These branches, measuring about 30 cm 1 ft long, were de-barked, mounted in plain sight, and used as weather-forecasting instruments. They can still be obtained today under names such as Maine Weather Stick. You can find some of these for sale on the Internet by...

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...

What Qualifies As A Blizzard

Meteorologists define blizzards according to the temperature and the wind speed. Blizzards are characterized by blowing and drifting snow, limited visibility, and cold temperatures. When the temperature drops below -7 C 25 F , accompanied by a wind of 30 kt 35 mi h or more, along with blowing snow, blizzard conditions exist. If the temperature falls to less than -12 C 10 F with winds of 39 kt 45 mi h or more, severe blizzard conditions exist. Although the meteorologist does not rigorously...

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,...

Layers Of The Atmosphere

Atmospheric Layers

The lowest layer of the atmosphere, rising from the surface to approximately 18 km 11 mi altitude, is the troposphere. This is where all weather occurs most of the clouds are found here. In the upper parts of the troposphere, high-speed rivers of air travel around the planet. The strongest of these rivers, called jet streams, blow in a generally west-to-east direction between 30 degrees north latitude 30 N and 60 degrees north latitude 60 N , and between 30 degrees south latitude 30 S and 60...

Symbols In General

Simple Weather 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...

Tornadoproofing A Building

Wind Blowing Roof Off House

It is doubtful that large buildings, gymnasiums, arenas, or shopping malls can be constructed with the reinforcement necessary to resist tornadic winds. The massive roofs would be torn off by airfoil effects. Small homes might be designed to withstand F3 or perhaps even F4 winds, but special construction methods and precautions would be necessary. Experience has shown that the windows are usually the first part of a house to be damaged by high winds. They are either blown out by the force of...

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

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...

Gases Near A Planet

Now imagine the shroud of gases that compose the atmosphere of a planet. Gravitation attracts some gas from the surrounding space. Other gases are ejected from the planet's interior during volcanic activity. Still other gases are produced by the biological activities of plants and animals, if the planet harbors life. On the earth, some gases are produced by industrial activity and by the combustion of fossil fuels. All the gases in the earth's atmosphere tend to diffuse into each other when we...

Semipermanent Pressure Regions

Near the 30 and 60 latitude lines, both in the northern hemisphere and in the southern hemisphere, the surface winds converge from, or diverge in, opposing directions. This gives the air an impetus to spin clockwise at 30 N and 60 S, counterclockwise at 60 N and at 30 S. The air also spins around the poles, clockwise in the arctic and counterclockwise in the Antarctic. The eddies near the 60th parallels tend to pull surface air inward, and the eddies near the 30th parallels and the poles tend...