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Click www.ondix.com to visit our student-to-student file sharing network. (Question #1) When atmospheric scientists describe the "weather" at a particular time and place or the "climate" of a particular region, they describe the same sort of characteristics: air temperature, type and amount of cloudiness, type and amount of precipitation, air pressure, and wind speed and direction. Weather is the current atmospheric conditions that include temperature, rainfall, wind, and humidity at any given place. If you stand outside, you can tell how hot it is by taking a temperature reading or feel if it is raining or windy, sunny or cloudy. All of these factors make up what we think of as weather. Weather is what is happening right now or likely to happen tomorrow or in the very near future. Climate, on the other hand, is the general weather conditions. For example, in the winter, we expect it to often be rainy in Portland, Oregon, sunny and mild in Phoenix, Arizona, and very cold and snowy in Buffalo, New York. But it would not be particularly startling to hear of an occasional January day with mild temperatures in Buffalo, rain in Phoenix, or snow in Portland. Meteorologists often point out that "climate is what you expect and weather is what you get. Climate is sometimes referred to as "average" weather for a given area. The National Weather Service uses values such as temperature highs and lows and precipitation measures for the past thirty years to compile "average" weather for any given area. However, some atmospheric scientists consider "average" weather to be an inadequate definition. To more accurately portray the climatic character of an area, variations, patterns, and extremes must also be included. Thus, climate is the sum of all statistical weather information that helps describe a place or region. Climate can be applied more generally to large-scale weather patterns in time or space (for example, an Ice Age climate or a tropical climate). To investigate how climate may be changing due to human influences, scientists use weather data from as far back as the historical record goes, as long as the data are accurate. Detailed daily weather data are collected at surface meteorological stations (weather stations) throughout the world. However, several factors can limit the accuracy of the data. For example, 1.)Many stations are in or near urban areas, which often experience warmer temperatures than the surrounding rural land. This is due to the heat absorbing properties of concrete and asphalt and the lack of shade and evaporative cooling from vegetation. This phenomenon is known as the "heat island effect." 2.)Many weather stations have been moved from rural locations to airports, making it difficult to interpret and compare measurements over time. (Question #2) Clouds look different depending on what they are made of. Water droplet clouds tend to have sharp, well-defined edges. If the cloud is very thick, it may look gray, or even black. This is because the sunlight is unable to pass through. Ice crystal clouds tend to have fuzzy, less distinct edges. They also look whiter. There are three basic cloud forms. Stratus clouds form in blanket like layers. Cumulus clouds are puffy clouds that appear to rise up from a flat bottom. Cirrus clouds form at very high altitudes out of ice crystals and have a wispy, featherlike shape. If rain or snow falls from a cloud, the term nimbo -for "rain"- is added to the cloud's name. High-level clouds form above 20,000 feet (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. High-level clouds are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon. The bases of mid-level clouds typically appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets; however, they can also be composed of ice crystals when temperatures are cold enough. Low clouds are of mostly composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow. Vertically Developed Clouds ; probably the most familiar of the classified clouds is the cumulus cloud. Generated most commonly through either thermal convection or frontal lifting, these clouds can grow to heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy through the condensation of water vapor within the cloud itself. A contrail, also known as a condensation trail, is a cirrus-like trail of condensed water vapor often resembling the tail of a kite. Contrails are produced at high altitudes where extremely cold temperatures freeze water droplets in a matter of seconds before they can evaporate. Billow clouds are created from instability associated with air flows having marked vertical shear and weak thermal stratification. The common name for this instability is Kelvin-Helmholtz instability. These instabilities are often visualized as a row of horizontal eddies aligned within this layer of vertical shear. Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air. Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed. Orographic clouds are clouds that develop in response to the forced lifting of air by the earth's topography (mountains for example). Pileus (Latin for "skullcap") is a smooth cloud found attached to either a mountain top or growing cumulus tower. (Question #3) Air masses are large bodies of air which have temperature and moisture characteristics nearly the same in the horizontal. The characteristics of an air mass derive from the region over which the air mass forms, called its source region. The source region is generally a region of light surface winds which allows the air to remain in contact with the surface long enough for the air to take on the temperature and moisture characterizes of the region over which the air is lying. As the air mass moves out of its source region, directed by the upper air flow, they may move across the location where you live bringing the temperature and moisture characteristics of the source region to you and they may encounter other air masses with different characteristics such as: 1.)Continental Arctic (cA): This air mass is characterized by extremely cold temperatures and contains very little moisture. These air masses form north of (or very near) the Arctic Circle and pole ward and usually affect the United States primarily in the wintertime. As shown by the image, they typically enter the United States from across Canada into the northern states and then move southeastward affecting the central and eastern part of the country. These air masses can move into Texas bringing clear, but cold conditions, the "Texas or Blue Norther." They bring bitterly cold temperatures and dry air to the affected areas. Continental Arctic air masses affect the continental United States usually in winter and rarely affect any of the states during the summer. 2.)Continental Polar (cP): Continental Polar air masses are also cold to cool and dry, but are not as cold as the Arctic air masses. Continental Polar air masses form farther south over central and southern Canada. These air masses bring cold air during the winter and cool, relatively clear, rather pleasant weather in the summer. As the continental Arctic and continental Polar move south across the warmer land, the lower portion of the air mass becomes warmer and may cause a few clouds to form. 3.)Maritime Polar (mP): Maritime Polar may be considered the cool, moist air mass which affects the United States. The source region for these air masses is the northern Pacific and the north-western Atlantic. Because they carry an abundance of moisture, they usually produce clouds and precipitation as they move inland and are forced upward by the rising land. 4.)Maritime Tropical (mT): Being from a source region in the Tropics and over water, this air mass is characterized by hot, humid conditions. These air masses occur frequently in all seasons across the south, southeastern and eastern United States. Cloudiness and precipitation are associated with this type of air. As the air is moved northward across the southern and eastern United States, it encounters rising land which forces the air upward producing much cloudiness and precipitation. 5.)Continental Tropical: These are the hot, dry air masses which originate over northern Mexico and the southwestern United States. This air mass enters the United States through New Mexico and Arizona and frequently moves eastward to northeastward bringing hot, dry air to western Texas. The leading edge of this air mass is often called the dry line where it encounters the maritime tropical air mass moving northward from the Gulf of Mexico. Frequently in the summer, rain showers and thunderstorms form along this dry line bringing much needed precipitation to western Texas. (Question #4) The Earth's surface spheres (atmosphere, hydrosphere, lithosphere, and biosphere) interact and behave much like a living community. The interaction of these spheres with solar energy and each other results in changing conditions which we refer to as weather and climate. Before reaching the Earth's surface, solar radiation passes through clouds and atmosphere, which reflect, scatter, absorb, and transmit various amounts of energy. The Earth's surface reflects some of the incoming solar radiation and absorbs the remainder. As the surface absorbs the energy, it heats and radiates the energy back into space. When the rates of absorption and radiation are equal (radiative balance) the Earth's temperature is stable. If the atmosphere did not exist, the Earth's surface would reach radiative balance at 33° Celsius (60° Fahrenheit) colder than it is. However, some gases in the atmosphere absorb some of the energy radiated from the surface. They heat and re-radiate energy back to the surface. In this way, the atmosphere maintains a higher surface temperature than the Earth would have without an atmosphere. This process is called the greenhouse effect. Much of the energy absorbed at the Earth's surface is radiated upward as infrared (IR) thermal energy. Several gases that occur naturally in the atmosphere absorb this infrared energy and re-radiate it back to the surface. Therefore, heat that would be lost to space is trapped near the surface. The effect of the atmosphere and its heat-absorbing gases warms the Earth's surface and the Earth's surface therefore reaches radiative balance at a higher temperature than if there were no atmosphere, or an atmosphere without IR-trapping gases. The term "greenhouse" is used to describe this phenomenon since these gases act like the glass of a greenhouse to trap heat and maintain higher interior temperatures than would normally occur. The atmospheric gases most responsible for this effect are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3). This "greenhouse effect" occurs naturally in our atmosphere and is responsible for the Earth's moderate surface temperature. Water vapor and carbon dioxide are the largest contributors to the natural greenhouse effect due to their overall abundance in the atmosphere. Methane, although at very low atmospheric concentrations, is a much more efficient absorber of infrared radiation than either H2O or CO2. Over a 100 year period, a molecule of methane can absorb about 25 times more IR energy than a molecule of carbon dioxide. A molecule of nitrous oxide can absorb about 320 times more energy than one of CO2. Therefore, although methane and nitrous oxide occur in very low concentrations, they exert a substantial influence because they are potent absorbers. Natural greenhouse gas concentrations have varied over time and shows variations in CH4 and CO2 concentrations and temperature anomalies for the past 200,000 years as derived from analysis of the Vostok ice cores from Antarctica. The major temperature trends from warmer (140,000 yrs BP) to colder (20,000 yrs BP) are called the interglacial (warmer) and glacial (colder) periods. CH4 varied from ~700 parts per billion by volume (ppbv) to ~300 ppbv, CO2 varied from ~300 parts per million by volume (ppmv) to ~150 ppmv. Temperature anomalies varied about 4-5° C (Lorius and Oeschger, 1994). Since the beginning of the Industrial Revolution about 200 years ago, atmospheric concentrations of greenhouse gases including CO2, CH4 and N2O have risen substantially. These increases are a result of a variety of anthropogenic activities such as the production and use of fossil fuels, as well as other industrial and agricultural activities. Naturally occurring CO2 undergoes a seasonal cycle. Atmospheric CO2 is taken up through photosynthesis of plants during the growing season and released through respiration throughout most of the year. These exchanges are about equal over the period of one year. This biospheric cycle is the major cause of the large seasonal oscillations in atmospheric concentrations of CO2. In addition, naturally occurring forest fires release CO2 when the vegetation is burned. This disturbance in the cycle is followed by a longer term uptake of CO2 by re-growth of vegetation lasting years to decades after the fire. Anthropogenic activities perturb the natural carbon cycle. During the last ~200 years, atmospheric concentrations of CO2 have increased about 25%. Because CO2 is not chemically active, terrestrial emissions either accumulate in the atmosphere or are taken up by the oceans or by the terrestrial biosphere (vegetation and/or soil). The largest single source of atmospheric CO2 is the burning of fossil fuels which accounts for ~80% of the annual emission from the Earth to the atmosphere (Matthews 1997). CO2 is also emitted from vegetation and soils from tropical deforestation and from savanna fires. A portion of the CO2 emitted from the Earth accumulates in the atmosphere while some is taken up by the oceans and by the re-growth of northern forests following abandonment and fires. Naturally occurring terrestrial N2O emissions are primarily due to microbial action in soils especially in tropical regions. These processes are strongly controlled by the status of oxygen, water, and nutrients in the soils. Anthropogenic activities have contributed to a 10% growth in methane concentrations in the atmosphere over the last ~200 years. Anthropogenic sources include land clearing, biomass burning, fossil fuel combustion, and nitrogen fertilizer use. Unlike CO2, nitrous oxide is chemically active; it is broken down in the stratosphere by sunlight (photolysis) and other chemical reactions. Naturally occurring terrestrial methane emissions are dominated by wetlands where anaerobic decay of organic material results in production and release of methane. Other natural methane sources include wild fires in both forests and grasslands, and wild animals. Atmospheric concentrations of methane have approximately doubled during the last two centuries. Anthropogenic sources include rice cultivation, agricultural animals such as cattle, animal waste, landfills, and the mining, processing, and distribution of fossil fuels. The emission of methane by both natural and anthropogenic sources varies seasonally. For example, methane is produced only when wetlands at high latitudes are warmed and thawed or when rice fields are flooded. Since methane is chemically active, it is broken down in the troposphere by hydroxyl (OH) radicals eventually forming carbon monoxide. Venus, Earth, and Mars travel in neighboring orbits around the sun. All of them are rocky planets, but only the earth has abundant life. Only the earth has conditions which support the presence of liquid water. The surface temperatures of these planets are governed by three factors: 1.)the amount of energy that they receive from the sun 2.)the composition of their atmospheres and 3.)their albedos. Venus is closer to the sun than the earth is. It has a very thick, dense atmosphere, made up mostly of carbon dioxide. The carbon dioxide acts like a blanket and keeps the sun's heat is trapped on the surface of Venus. This is called the Greenhouse Effect. Scientists tell us that the temperature on Venus is about 890 degrees Fahrenheit. This is 477 degrees Centigrade (or Celsius). At this temperature lead and tin would be melted. Carbon-based life forms would be vaporized. Water would boil away. It is difficult to discover what the surface of Venus is like. Our earth probes do not survive long in the heat, and the dense atmosphere makes it difficult to transmit information and signals. Earth would be too cold for life if it had no atmosphere. The atmosphere holds enough of the sun's heat to make life possible here. Temperatures on earth range from a high of perhaps 130 degrees Fahrenheit to about -90 Fahrenheit. There are places on earth in which it is challenging for us to stay alive. For example, the temperature on earth in Los Angeles is about 70 degrees Fahrenheit, which is 21 degrees Centigrade. This is pleasant for carbon-based life forms, though some with adaptations for cold might feel uncomfortably warm. Mars is the furthest rocky planet from the sun. It is a smaller planet than the earth, and has lost much of its atmosphere. The weaker gravity of Mars allows more atmospheric molecules to escape into space. As a result of Mars' very thin atmosphere, solar heat escapes easily. The temperature on Mars can be as high as 50 degrees Fahrenheit (10 C) at the equator and as low as -185 degrees Fahrenheit (-120 C) at the poles. Carbon-based life forms could survive at the warmer temperatures (given oxygen and other necessities) but the water in our cells freezes at 0 C, and maintaining our body heat would be challenging in even the warmest areas. We would have to really focus on staying warm at night and during the winters. 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