The atmosphere surrounding our planet Earth sustains life and affects our lives in inumerable ways. It contains life-supporting oxygen and limits the effects of radiation from the Sun. Climate and weather are a result of the physics and chemistry of the atmosphere and its interactions with the landforms and oceans of Earth. Over the centuries people have gathered a wealth of information about climate and weather but there is much that is not yet understood.

  1. What is CLIMATE? Climate is the overall picture of weather during periods of seasons or years. Historical records of various sorts (including geological and recorded history) show us how the climate of Earth has changed throughout its history. In recent historical times human activities such agriculture, development of cities, use of technology, and changing of landscapes has been causing additional climate change.

  2. What is affected by climate changes? The growing of crops to feed the populations of the world, is directly affected by climate change. Food production is totally dependent on favorable growing conditions. Extensive droughts, for example, can result in deaths from starvation and can cause serious economic problems when the hungry populations migrate to more fortunate regions.

  3. What is WEATHER? Weather is the air temperature, cloud cover, precipitation, and wind at any particular time in any particular place. Weather reflects the prevailing conditions of the air masses overlying the land and seas over the entire globe. Weather patterns over a period of time present a picture of climate.

  4. What causes changes in the weather? The entire atmosphere surrounding Earth is in constant motion caused by the uneven heating effect of the sun due to the spin of the Earth on its axis as it orbits the Sun. This causes the atmosphere to be composed of distinct air masses that have different temperatures, different amounts of moisture, different atmospheric pressures. To add to the complexity, the air masses are moving at different speeds at different levels above Earths surface. Each air mass brin

  5. What is the physical structure of our atmosphere? The atmosphere is about 50 miles thick. It consists of several layers of air identified by their density. Each layer varies in depth (thickness). Closest to the surface of Earth is the most dense layer, the troposphere. This layer is about 3 miles deep over most of the Earths surface. It is warmest close to the surface of Earth and gets cooler further out toward space.

  6. What about the outer layers of the atmosphere? The layer above the troposphere is the tropopause. This second layer, about 3-5 miles deep, increases in temperature as it is further away from the surface of Earth. It is in the two lowest layers of the atmosphere - the troposphere and tropopause layers - that the development of airmasses causes our weather and climates. The tropopause ends at about 6-12 miles above the surface of Earth where it meets the stratosphere which is about 20 miles thick and reaches to about 30 miles above the surface of Earth.

  7. What is the chemical composition of our air? The lower layers of the atmosphere form a thin enveloping layer of gases of which 78 percent is nitrogen, 21 percent is oxygen, and the remaining 1 percent includes trace gases. Water vapor (an invisible gas) and water droplets (cloud, fog, or rain) or ice particles (frozen water droplets), and the gas carbon dioxide are present in generally small quantities but are important.

  8. What are clouds? Clouds are accumulations of tiny water droplets in the lower atmosphere. They are of different shapes and even colors. Some are high in the sky. Others so low that they almost touch the ground. Some days there are no clouds. Where did they go? Clouds look quite substantial as we see them from the ground but they are composed of loosely spaced water droplets and are actually not very solid at all. They form when the composition and movement of an air mass creates the right conditions.

  9. When do clouds form? Clouds form when moist air cools. Moist air is air that contains water vapor (an invisible gas). In nature, air cools as it rises away from the ground; it also cools when it mixes with a colder air mass. At a certain cooler temperature (the "dew point") which depends upon the amount of water vapor in the air, the water vapor condenses into tiny, visible water droplets. We see these tiny droplets as clouds. If they are very close to the ground we see them as fog. These droplets are not big enough to fall as rain.

  10. Are there different kinds of clouds? Yes. The highest clouds are typically about 17,000 to 50,000 feet above the ground. These are the cirrus clouds which are composed of ice crystals and appear as white, silky filaments, patches or bands. Clouds that form beneath cirrus clouds include the stratus or flat, layered clouds. Nimbus clouds are also lower than cirrus; they are dark, rain clouds The clouds that form closest to the ground are cumulus or heaped clouds which have a flat base. These clouds too can provide rain.

  11. What is wind? Wind is air that is moving across the surface of Earth. It is caused by the movement of the air masses in the lower levels of the atmosphere. Many winds are seasonal and have names: the sirocco is a hot, dry wind that blows from the south or southeast out of the deserts of North Africa or Saudi Arabia; in coastal southern California, Santa Ana winds are hot, dry, late summer, north or northeast winds that blow from the inland high deserts and through the mountain passes across the California coastal plain.

  12. What is a "Trade Wind?" Trade winds are strong, steady winds named because, through the ages, they have helped merchant ships move across the oceans. These winds blow from east to west and push on the waters of the oceans as they blow across their surface. The friction of the moving air across the water sets ocean currents in motion and keeps them moving in the direction of the wind. There are two other belts of steady winds; one blows from west to east in the mid latitudes, the other blows from east to west near the poles.

  13. What happens when trade winds do not blow? Most years trade winds blow steadily from South America and west across the Pacific pushing surface coastal waters westward. This creates an upswelling of cool water. When the trade winds do not blow, the waters warm up. This warm water gradually spreads partway across the Pacific and as far north as California and Washington. Vast changes in the global circulation of air masses result and strange weather is experienced around the world. This phenomenon is called El Nino and it happens irregularly sometimes two or as many as ten years apart.')

  14. Where does the energy come from that stirs up our atmosphere? It comes from the Sun whose radiated sunlight passes through the atmosphere and heats up land and oceans, rivers, forests and fields. The warmed land and water radiates some of the heat, back up into the air resulting in a warming of the air that is close to the ground or water. The warmed air rises and cooler air sinks down to take its place. This rising of warm air and sinking of cooler air is the basis for most movement in the air masses of the atmosphere.

  15. Does the radiation from the Sun heat up Earth evenly all around the globe? No. Sunlight shines more or less directly down to Earth at the equator but passes at an angle through the atmosphere toward the poles. This means that while the sun passes through about 50 miles of atmosphere at the equator, it passes through much more atmosphere in order to reach the more northern and southern latitudes. The result is that the ground is much warmer around the equator than at the poles. This differences in the temperatures causes air mass movement when warm tropical air rises and cooler northern latitude air sinks down to take its place.

  16. Does all the sunlight energy that reaches Earth stay here? No. When sunlight falls on Earth a certain amount of it is reflected back into space. Of the sunlight falling on bare ground, 10-20 percent is reflected; a green forest reflects 3-10 percent; and fresh snow reflects 80-90 percent (this is why it remains so cold at the poles even though the sun shines for long periods). Perhaps 30 percent of all the sunlight reaching Earth from the Sun is reflected back into space by clouds, snow, land and water surfaces.

  17. Is warming the only factor that causes air masses to move? No. Air masses are affected by the spinning of the Earth on its axis as it orbits the Sun. The spinning of Earth causes air masses to rotate. In the southern hemisphere the air masses rotate clockwise; in the northern hemisphere they rotate counterclockwise. This phenomenon can be seen in weather satellite photographs. When the rotation becomes a tight, rapidly spinning whorl the air mass is called a cyclone. Cyclones are our biggest storms.

  18. Is the climate of Earth still changing? Yes. The climate of Earth has been in a constant state of change ever since the planet was first formed and it is still changing. The change happens relatively slowly and we have only recently developed the tools and the knowledge necessary to discover the patterns of change over past eras and to record the gradual changes that are happening during our own lifetimes.

  19. How can we find out what the climate of Earth was like hundreds of years ago? Detailed, accurate records of the weather have only been kept for the past few decades. But, there are lots of places to look for clues - rock formations, ocean sediment cores, pollen in amber, or tree rings. When 17th century Dutch artists painted their now famous winter landscapes they were illustrating the fact that there were many extremely cold winters in the 17th-century. This period in history is called the Little Ice Age. The generally cold climate of the period is confirmed in the records of their grape harvests kept by French winemakers for the past 500 years.

  20. What do we know about past climates on Earth? Geological records suggest that the first Ice Age ocurred about 2.3 billion years ago and the most recent Ice Age extended from about 22,000 through 12,000 years ago. During that time, glaciers covered much of the north including Canada and northern Europe and Asia. Global temperatures were about 10 degrees F. cooler than today. Studies seem to show that climate changes can be surprisingly abrupt. It seems an ice age can develop in as short a period as an average human life span. Some scientists believe that we are overdue for the development of another ice age.

  21. What happened in between the ice ages of past eras? During the Pleistocene era, extending back about 600,000 years there were four ice ages and in between these the temperature was about 5 degrees F. warmer than today. Before that time, going back about 100 million years to the Cretaceous period, global temperatures appear to have been perhaps 18 degrees F. warmer than today. Ocean levels rose and water spilled over onto the land creating differently shaped land masses. The possibility that in our current era human activity is causing global warming is a hotly debated and so far undecided issue.

  22. What about weather forcasting? At one time weather forecasting was simply a matter of experience gained from careful observations of weather patterns. Such experience was passed on through such proverbs as Birds flying low Expect rain and a blow.This observation has a scientific basis because birds adjust their flight to the optimum density. When the air pressure is low, the optimum density for bird flight is also low. And, when air pressure is low, rain and wind can be expected.

  23. How accurate are weather proverbs? Today we have generally replaced weather story-telling, cautionary tales, and proverbs with easily retrievable, digitally recorded data. However, for many of us the appeal of a story or a proverb is compelling and more likely to be remembered. Take for example the proverb Flowers smell best just before a rain. This has a scientific basis because scents are more easily detected in moist air, and moist air very often foretells rain.

  24. When was weather forecasting first based on real data? As early as 900 BC Babylonians recorded wind directions; and in the 500s BC the Greeks recorded rainfall. In Oxford, England, William Merle kept weather records from 1337-1344. All data until the mid 1900s were from field observations or weather balloons. The idea that weather forecasting could be achieved by formulating equations of atmospheric motion emerged in 1922 but was not successfully implemented until 1950. Numerical weather prediction using computers to do the immense calculations is now standard.

  25. When did weather forcasting start to become more reliable? During WW2 one of the first modern computers, a huge machine named ENIAC was used to improve weather forecasting by means of much faster mathematical processing of weather data. Now, weather data collected by Earth orbiting satellites is processed in the U.S. by a new supercomputer called Cyber 205A and in the UK by a Cray-XMP. These computers use the data to model how the weather will behave during the following several days. Their one-day forecasts are fairly reliable but further into the future than one day the results are only modestly accurate.

  26. How long have weather satellites been used for collecting data about the atmosphere? The first weather satellite was launched on April 1, 1960 from Cape Canaveral in the U.S. The satellite was TIROS 1 (Television and Infrared Observation Satellite) and it sent television images of Earth from space showing cloud systems. On April 10, just over a week after its launch, TIROS sent back images showing that a typhoon had developed east of Australia. (Tropical storms in the western Pacific are called typhoons but similar storms in the eastern Pacific and the Atlantic are called hurricanes.)

  27. What are weather satellites? They are automated spacecraft designed to operate reliably with little human intervention once they are launched. They contain sophisticated electronic equipment to gather visual and other data and relay it to Earth. There are now two types of weather satellites. About five of the geostationary (GOES) type are in orbit. Each one can view about 38 percent of the surface of the Earth and together they continuously monitor the weather at hourly intervals. They are the source of the cloud pictures on nightly television weather reports. The other type of weather satellite (POES) is put into polar orbit.

  28. What can weather satellites usefully reveal? Weather satellites record images using both visible light and infrared so they can record during the day and at night. They record not only cloud systems but sea surface temperatures and various other data from the atmosphere and the ground. Both GOES and POES satellites also provide data that is not specifically related to the weather. Because they monitor vegetation growth they provide data that is used to forecast locust plagues in Africa. They can track migrating birds and swarms of bats, and can map forest fires.

  29. What are the names of some local winds around the world? Trade winds and the Santa Ana have already been mentioned but there are many more including: the sirocco of Africa; the bolon, nirta or tamboen of Sumatra; the Tehuantepecer of Mexico; the puelche which blows across the Andes mountain ranges of South America; the knik of Alaska; the kona and the mauka of Hawaii; and the mistral the dry, cold northerly wind that blows down the Rhone valley in France.

  30. What is radar? Radar is an acronym for radio detection and ranging. Radar was simultaneously developed in several countries. It was seen as useful to track icebergs, to prevent ship collisions, and to track plans and ships. It was soon discovered that the radio waves not only bounced off such solid objects but also echoed back from such elemental events as rain storms. Operational, meteorological (weather monitoring) radar in the form of a national radar grid was first authorized in the US in the mid 1950s.

  31. Why is the study of weather called meteorology? The answer to this question refers back to ancient Greece where a meteor was any atmospheric penomenon that might appear in the sky. This of course included clouds, rain, rainbows etc. Aristotle, the ancient Greek philosopher-scientist, wrote a book called Meteorologica which explained all that was then purported to be known about the sky. In this early textbook of atmospheric science Aristotle described hurricanes as being caused by evil winds falling upon good winds with a resulting moral conflict. Modern explanations are quite different.

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