The atmosphere is a cloud of gas and suspended solids extending from the Earth's surface out many thousands of miles, becoming increasingly thinner with distance but always held by the Earth's gravitational pull.
The envelope of gas surrounding the Earth changes from the ground up. Five distinct layers have been identified using... thermal characteristics (temperature changes), chemical composition, movement, and density.
Mesosphere The mesosphere extends from the top of the stratosphere to about 56 miles (90 km) above the earth. The gases, including the oxygen molecules, continue to become thinner and thinner with height. Stratosphere The Stratosphere extends from the top of the troposphere up to around 31 miles (50 km) above the Earth's surface. This layer holds 19 percent of the atmosphere's gases but very little water vapor. Troposphere The troposphere begins at the Earth's surface and extends from 4 to 12 miles (6 to 20 km) high. This is the layer of the atmosphere in which we live.
Exosphere The Exosphere is the outermost layer of the atmosphere. It extends from the top of the thermosphere to 6,200 miles (10,000 km) above the earth. In this layer, atoms and molecules escape into space and satellites orbit the earth. Thermosphere Above the mesosphere the thermosphere extends up to near 375 miles (600 km) above the earth. This layer is known as the upper atmosphere.
Weather The term "weather" refers to the momentary conditions of the atmosphere. We usually think of the weather in terms of the state of the atmosphere in our own part of the world. The weather in any one area, however, may eventually influence, or be influenced by, the weather a great distance away. Weather usually changes from hour to hour or from day to day. Over many years, certain conditions are characteristic of the weather in an area. The average weather in an area, as well as its variations and extremes over many years, is called climate. Like weather, climate can change, too, but much more slowly.
Thunderstorms • It is estimated that there are as many as 40,000 thunderstorm occurrences each day world-wide. This translates into an astounding 14.6 million occurrences annually! The United States certainly experiences its share of thunderstorm occurrences.
The figure shows the average number of thunderstorm days each year throughout the U.S. The most frequent occurrence is in the southeastern states, with Florida having the highest number 'thunder' days (80 to 100+ days per year). It is in this part of the country that warm, moist air from the Gulf of Mexico and Atlantic Ocean
All thunderstorms require three ingredients for their formation: • Moisture, • Instability, and • a lifting mechanism.
Water temperature also plays a large role in how much moisture is in the atmosphere. Recall from the Ocean Section that warm ocean currents occur along east coasts of continents with cool ocean currents occur along west coasts. Evaporation is higher in warm ocean currents and therefore put more moisture into the atmosphere than with cold ocean currents at the same latitude.
Therefore, in the southeastern U.S. the warm water from the two moisture sources (Atlantic Ocean and Gulf of Mexico) helps explain why there is much more rain in that region as compared to the same latitude in Southern California.
Instability • Air is considered unstable if it continues to rise when given a nudge upward (or continues to sink if given a nudge downward). An unstable air mass is characterized by warm moist air near the surface and cold dry air aloft.
Sources of Lift • Typically, for a thunderstorm to develop, there needs to be a mechanism which initiates the upward motion, something that will give the air a nudge upward. This upward nudge is a direct result of air density. • Some of the sun's heating of the earth's surface is transferred to the air which, in turn, creates different air densities. The propensity for air to rise increases with decreasing density. This is difference in air density is the main source for lift and is accomplished by several methods.
This is the most dangerous stage when large hail, damaging winds, and flash flooding may occur A cumulus cloud begins to grow vertically, perhaps to a height of 20,000 feet
A tornado is a violently rotating (usually counterclockwise in the northern hemisphere) column of air descending from a thunderstorm and in contact with the ground. Although tornadoes are usually brief, lasting only a few minutes, they can sometimes last for more than an hour and travel several miles causing considerable damage. The United States experiences more tornadoes by far than any other country. In a typical year about 1300 tornadoes will strike the United States. The peak of the tornado season is April through June and more tornadoes strike the central United States than any other place in the world. This area has been nicknamed "tornado alley."
Climate "Climate" refers to all weather conditions for a given location over a period of time. Weather can change from hour to hour, from day to day, from month to month, or even from year to year. For periods of 30 years or more, however, meteorological records reveal that distinct weather conditions prevail over different parts of the world. Each set of conditions forms a climate type, and the area covered by a particular type is called a climate region.
Some parts of the world are hot and rainy nearly every day; they have a tropical wet climate. Others are cold and snow-covered most of the year; they have a polar climate. Between the icy Poles and the steamy tropics are many other climates that help make the Earth unique.
Climate Controls • Climate ControlsWhether we have hot or cold seasons, lots of rain or very little is determined by how temperature, moisture, wind, and air pressure mix in Earth's atmosphere. Listed below are "climate controls" and how they affect weather and climate: • Latitude—Earth's surface and atmosphere receive varying, changing amounts of energy from the sun. Generally, the areas around the Equator receive more while the polar areas receive less. Therefore, areas of lower latitude tend to be warmer and polar areas tend to be colder.Land and Water—Because land and water heat at different rates (land heats and cools more quickly than water), areas near large bodies of water tend to have their climates moderated. That means that in general, areas along a shoreline will have milder summer and winter temperatures. Also, bodies of water such as oceans or seas provide lots of moisture for the atmosphere. This is especially true about warm bodies or currents of water.Landforms—Landforms such as hills or mountains can alter wind flow. Because winds can be forced upwards by an elevated landform, the exposed (windward) side can often have a different weather and climate than the sheltered (leeward) side. As air travels up a mountain, moisture is "squeezed" out of the air as it cools, condenses, and falls as precipitation. Air temperature and the amount of moisture in the air are usually decreased as it flows down the sheltered side of the mountain.Elevation—Generally, the higher you go in the lower portion of the atmosphere, temperature, moisture, and air pressure decrease.Ocean and Wind Currents—The water in Earth's oceans and the air in Earth's atmosphere are constantly moving. The movement can be across, up, or down. This process circulates cool or warm air and water around Earth.