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Composition of the Atmosphere The atmosphere mostly consists of nitrogen (78%), oxygen (21%), and argon. 99% composed of Nitrogen and Oxygen Remaining 1% made up of small amounts of other gases Structure of the Atmosphere Atmosphere composed of several layers Structure of the Atmosphere Troposphere Closest to Earth Altitude 0-10 km Contains most of the mass of the atmosphere Weather occurs here, pollution collects Upper limit called tropopause Tropopause is where gradual decrease in temperature stops Stratosphere -Above troposphere -Altitude 10-50 km -Contains mostly ozone -Ozone absorbs more UV radiation, so this layer is heated -Upper limit called stratopause -Stratopause is where gradual increase in temperature stops Mesosphere Above stratosphere Altitude 50-80 km No concentrated ozone here, so temperature drops again Upper limit called mesopause Mesopause is where gradual decrease in temperature stops Thermosphere Above mesosphere Altitude 80 km and above until outermost boundary of atmosphere Contains a small part of the atmosphere’s mass Little air that is in this layer increases in temperature again to greater than 1000C The Ionosphere The thermosphere can be identified in two parts- the ionosphere and the exosphere. Ionosphere: 80 km-640 (about 400 miles = 640 km). It contains many ions and free electrons (plasma). Auroras occur in the ionosphere. Exosphere Outermost layer of Earth’s atmosphere Light gases like helium and hydrogen found here Above exosphere is outer space No clear boundary between atmosphere and space Atmosphere Energy The Sun is the source for all energy in the atmosphere. Three ways the energy transfer occurs: Radiation Conduction Convection Flash Animation Radiation Radiation is the transfer of energy through space by visible light, UV radiation, and other forms of electromagnetic waves Conduction Conduction is the transfer of heat energy that occurs when particles collide Through conduction, Earth’s surface transfers energy to nearby air particles in troposphere. Conduction only affects small layer of atmosphere. Convection Convection is the transfer of heat energy by the flow of a heated substance Pockets of air near Earth’s surface are heated, become less dense and rise As warm air rises, it expands and starts to cool. As it cools, its density increases and the cooler air sinks. As it sinks, it warms again and process starts over. Temperature and Heat Temperature-measurement of energy of a substance; interprets atmospheric processes. Heat-transfer of energy from two objects of different temperatures; fuels atmospheric processes. Pressure and Density Air pressure increases towards Earth’s surface because of the greater mass of the atmosphere above you. Atmospheric pressure decreases with height because there are fewer gas particles above you. Density is proportional to amount of particles. Wind Air moves in response to density imbalances created by the unequal heating and cooling of Earth’s surface. These imbalances, in turn, create areas of high and low pressure. Wind can be thought of as air moving from an area of high pressure to an area of low pressure. Humidity Humidity-amount of water vapor in air. Relative humidity-ratio of water that air contains and the maximum amount of water the air could contain. Warm air is more capable of holding more moisture that cold air. Do we usually ever complain of humidity in winter? Clouds Dew point-temperature at which air must be cooled to reach saturation. Condensation-phase change from gas to liquid; only occurs at saturation. Lifted Condensation Level-LCL; point at which condensation occurs. Cloud Formation Air masses of different temperatures collide. The less dense, warmer air mass rises over the more dense, colder air mass. As the warm air rises, it cools, and once it reaches the LCL, water vapor will condense around condensation nuclei to become a cloud, if the density of condensation nuclei is great enough. Condensation nuclei-particles in the air around which cloud droplets can form. Precipitiation Coalescence-occurs when cloud droplets collide and join together to form a larger droplet. When the droplet becomes too heavy to be held aloft, gravity takes over and it falls to Earth as precipitation. Another Method of Cloud Formation Orographic Lifting-air mass is forced to lift due to topography, cooling down quickly in the process, causing condensation and cloud formation. Meteorology Weather-current state of the atmosphere. Climate- describes the average weather over a long period of time Air Masses A large body of air with similar -TEMPERATURE - HUMIDITY Temperature • Warm • Cold Humidity • Moist • Dry Air Masses’ Characteristics Source Regions Over land: drier. Over water: more moist. Types of Air Masses DESCRIPTION FORMED 1. Maritime: (m) CONDITION moist LOCATION (marina/water) 2. Continental:(c) dry (continents/land) 3. Tropical: (T) warm (tropics) 4. Polar: (P) cold (poles) Types of Air Masses Maritime Tropical (mT) Continental Tropical (cT) Maritime Polar (mP) Continental Polar (cP) Types of Air Masses cP Continental Polar mP Maritime Polar Dry, cold air to central and eastern US. mP Maritime Polar Moist, cold air to east areas of the Canada Moist, cold air to west coast of the US. mT Maritime Tropical mT Maritime Tropical Moist, warm air to west coast of the Mexico. Dry, warm to Desert SW Moist, warm air to south Mr. Fetch’s Earth Science Classroom east coast of the US. Air Mass Modification mP Maritime Polar Moist, cold air to west coast of the US. Mr. Fetch’s Earth Science Classroom Weather Systems Coriolis Effect-caused by Earth’s rotation; causes moving objects to deflect right in N. hemisphere, left in S. hemisphere. This effect creates a global wind system that transports air masses. Three Types of Wind Systems Trade winds Prevailing westerlies Polar easterlies Trade winds Move between equator and 30° N and S latitude. Air sinks, warms, and returns to equator in westerly direction. Prevailing Westerlies Occurs between 30° and 60° latitude Moves in opposite direction of trade winds Moves weather across U.S. Polar Easterlies Occur between 60° and poles Cold air Fronts A boundary between two air masses: COLD FRONTS WARM FRONTS STATIONARY FRONTS Occluded fronts When air masses meet… mP Maritime Polar Moist, cold air to west coast of the US. mT Maritime Tropical Moist, warm air to south Mr. Fetch’s Earth Science Classroom east coast of the US. Cold Fronts -When cold air hits warm air. - Warm air is forced violently up. - Rising air creates clouds, rain, and storms. -Heavy precipitation for a short period of time likely. (FRONTAL LIFTING) Mr. Fetch’s Earth Science Classroom Cold Fronts -When cold air hits warm air. - Warm air is forced violently up. - Rising air creates clouds, rain, and storms. (FRONTAL LIFTING) -Flash Animation Cold Fronts “COLD FRONT” … umm its gets colder , duh! Warm Fronts -When warm hits cold air. - Warm air gently glides up over the cold air. - Rising air creates clouds and showers. (Less Violent). -Light precipitation for a longer period of time likely. Mr. Fetch’s Earth Science Classroom Warm Fronts “WARM FRONT”… right, it gets warmer, good. Stationary Front - When a warm or cold front stops moving. - Usually several days of clouds and showers. Occluded Front Occluded front occurs when cold front wraps around warm front. SYSTEM TYPES LOW PRESSURE: cyclones 1. form along fronts. (Unstable) 2. rising air. 3. winds rotate counter-clockwise around low pressure systems. 4. Rainy, stormy weather The high’s and low’s of weather… HIGH PRESSURE: anticyclones 1. sinking air. (Stable) 2. The sinking air stops clouds from forming. 3. winds rotate clockwise around high pressure systems. 4. Sunny, clear weather How Thunderstorms Form For a thunderstorm to form, three conditions must exist. Abundant source of moisture 2. Mechanism to lift air so that the moisture can condense and release latent heat. 3. Instability in the atmosphere 1. Limit of Thunderstorm Growth The air in a thunderstorm will keep rising until: 1. Stable air is reached that it cannot overcome 2. Rate of condensation is not able to generate enough latent heat to keep the cloud warmer than the surrounding air Three Types of Thunderstorms 1) air mass thunderstorm-results from air rising due to unequal heating in an air mass. 2) sea breeze thunderstorms-results from extreme temperature differences air over land and water. 3) frontal thunderstorms-results from advancing cold fronts. Stages of Thunderstorm Development Three Stages 1) Cumulus 2) Mature 3) Dissipation Flash Cumulus Stage Air rises vertically. Moisture condenses into visible cloud. Coalescence occurs. Mature Stage Precipitation falls, cooling the air surrounding it and creating a downdraft. The updraft and downdraft creates a convection cell. Equal amount of updraft and downdraft creates a cumulonimbus cloud. Dissipation Stage Warm air is gone, cooled by downdraft. Updraft ceases. Lingering downdraft persists. Tornadoes A tornado is a violent, whirling column of air in contact with the ground. Before touching ground it is called a funnel cloud. Fujita intensity scale-classifies tornadoes from F0 to F5, F5 being the strongest wind speeds. Tornadoes Tornadoes are visible due to dust, debris, and condensation. Created when wind speed and direction change suddenly with height, a process called wind shear. Flash Tropical Cyclones Tropical cyclones are large, rotating, lowpressure storms that form over water during summer and fall in the tropics. Two things to form: 1) Abundance of warm water 2) Disturbance to lift air and keep it rising Tropical Cyclones These conditions exist in all tropical oceans except the South Atlantic Ocean and the Pacific Ocean west of the South American Coast. Tropical Cyclone Most tropical cyclones begin as a disturbance, or a low pressure system that occurs close to the surface of tropical ocean. Once the low pressure system acquires a cyclonic rotation, it is known as a tropical depression. Forms of Tropical Cyclones 0-65 km/hr-tropical depression 65-120 km/hr-tropical storm 120 km/hr +-hurricane Saffir-Simpson hurricane scale classifies hurricanes from Category 1 to Category 5, Category 5 having the strongest win speeds Flash Hurricanes Eye-calm center of the storm Eyewall-band immediately surrounding the eye that contains the strongest winds in a hurricane. A hurricane will last until it can no longer produce enough energy to sustain itself. This usually happens when: 1) Hurricane runs over land. 2) Hurricane runs into colder water Hurricanes The Saffir-Simpson hurricane scale classifies hurricanes according to wind speed, air pressure in the center, and potential for property damage. It ranges from Category 1 hurricanes to Category 5 storms, which can have winds in excess of 155 mph. Hurricanes A hurricane will last until it can no longer produce enough energy to sustain itself. This usually happens when: 1) Hurricane runs over land. 2) Hurricane runs into colder water Global Warming – Global warming, a phenomenon related to the greenhouse effect, is an increase in Earth’s average surface temperature. – The greenhouse effect is a natural phenomenon in which Earth’s atmosphere traps heat in the troposphere to warm Earth. Human activities, especially the burning of fossil fuels, are largely responsible for increased levels of carbon dioxide, which is the main greenhouse gas that causes global warming. Global Warming and Severe Weather Increased temperatures of ocean waters due to global warming have been linked to the increase in severity and frequency of tropical cyclones.