The Siege Phase

As the edge of the eyewall approaches, the sound is like that of a freight train passing. The house in which you sit begins to shake, even though its exterior walls are made of solid concrete. You can hear things smacking against those outer walls and against the plywood covering the windows. The air becomes filled with tree limbs and whole palm tree tops, unsecured bicycles, lawn mowers, boats, Spanish tiles, broken glass, and big signs. Automobiles are over turned, and some smaller cars are...

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...

Axial Tilt

The seasons are caused mainly by the tilt of the earth's axis. The earth's orbit lies in a single plane, known as the ecliptic plane. The planetary axis is not perpendicular to the ecliptic plane. If that were the case, the sun would always be above the horizon for 12 hours each day and below the horizon for 12 hours each night, except at the poles, where the sun would follow the horizon, making a complete circle around the compass every 24 hours. In all the inhabited parts of the world, 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...

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...

The Fahrenheit Scale

In much of the English-speaking world, and especially in the United States of America, the Fahrenheit temperature scale F is used by lay people. A Fahrenheit degree is the same size as a Rankine degree. However, the scale is situated differently. The melting temperature of pure water ice at sea level is 32 F, and the boiling point of pure liquid water is 212 F. Therefore, a temperature of 32 F corresponds to 0 C, and 212 F corresponds to 100 C. Absolute zero is represented by a reading 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...

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...

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....