Earth s Atmosphere: Some Facts.

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1 Some terminology Weather is the state of the atmosphere at a given place and time. Temperature, precipitation, cloudiness, humidity, and wind are all components of weather. Climate is a composite of weather patterns from season to season, averaged over many years. e.g.- Miami and Los Angeles have warm climates: summers are hot and even the winters are warm. In contrast, New York and Chicago have cooler climates with winter snow.

2 Earth s Atmosphere: Some Facts. The Earth's present-day atmosphere is dramatically different from its original one. As the Earth initially coalesced into a rocky sphere, its atmosphere consisted mainly of hydrogen with smaller amounts of helium and other gases. Most of the hydrogen and helium escaped into space shortly after the Earth formed, 4.6 billion years ago. A second atmosphere then formed as volcanoes gave off gases trapped within the planet, and the Earth's gravitation attracted other gases from outer space

3 Earth s Atmosphere: More Facts. By studying the atmosphere of our two nearest neighbors, Venus and Mars, and by analyzing the compositions of old rocks on the Earth's surface, scientists have deduced that this second atmosphere consisted of carbon dioxide (C02), nitrogen (N2), and water vapor (H20), with smaller amounts of methane (CH4), ammonia (NHA hydrogen (H,), and carbon monoxide (CO). Oxygen was present in trace quantities only. This atmosphere formed within the first 500 million years of Earth history. Most modern organisms would rapidly suffocate and die in such an environment!

4 Evolution of the Earth s Atmosphere Primitive atmosphere contained carbon dioxide, and other gases

5 Evolution of the Earth s Atmosphere As plants evolved, the composition of the atmosphere began to change: Oxygen (released during photosynthesis) began to accumulate.

6 Evolution of the Earth s Atmosphere The modern atmosphere is composed mainly of nitrogen (78%) and oxygen (21%) with small concentrations (1%) of water, carbon dioxide and other gases: The ration of O to CO2 is maintained by dynamic exchange among plants and animals.

7 Major types of clouds: Clouds form when air cools below its dew point. Stratus clouds are stratified, or layered, often blanketing the entire sky with a uniform cover. Cirrus clouds are wispy. curly, or stringy They usually signal fair weather ahead. Cumulus clouds are lumpy or heaped. The weather they bring depends on their height and size. Origin of names: Cirrus= a filament like Stratus = layers Alti = high Nimbus = rain

8 The exosphere: above 500 km, which merges with the thin gases of interplanetary space. Layers of the Earth s Atmosphere The thermosphere: 60 to 500 km The mesosphere: 45 to 60 km The stratosphere: 6 to 45 km (contains the ozone layer) The troposphere: sea level to 6 km

9 Mechanisms that cause air to rise: Frontal wedging: When a mass of warm air comes in contkict with cool air, the warm air rises over the cool air. Orographic lifting When air blows against a mountainside, it is forced to rise. Convection-convergence If one portion of the atmosphere becomes warmer than surrounding air, the warm air expands and rises. Surface air then rushes in to replace the rising air and converges with it.

10 Air Pressure, air movement, and weather

11 Air Pressure, air movement, and weather

12 Weather-map view of Cyclones Origin Circulation systems alternate producing. They result from circulating high and low pressure differences between the equator and poles.

13 Hurricanes and Typhoons: Derivation of the terms: The words Hurricane aid Typhoon describe tropical cyclones with maximum sustained speed of 75 mph. Hurricane from the West Indian word huracan meaning "big wind'. Describes Atlantic and East Pacific storms Typhoon, form the Chinese word taifun meanings great wind, describes West Pacific storms

14 A cyclone is an atmospheric low-pressure system that gives rise to roughly circular, inward-spiraling wind motion, called vorticity. Because of the Coriolis effect, Such systems rotate in a counterclockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere

15 Origin of Cyclones: Circulation systems are alternately producing and resulting from circulating high and low pressure differences between the equator and poles. Cyclone Central low pressure with higher surrounding pressure Characterized by low-level convergence and ascension of air masses Anticyclone Central high pressure with lower surrounding pressure. Characterized by low-level divergence and subsiding air masses

16 Formation of Cyclones: Cyclones are fueled by warm moist air As this air rises it condenses releasing the Went: heat stored within it Extremely moist air is needed to produce and sustain tropical storms Only very warm air is capable of transporting the moisture required For this reason these storms are only formed over water with temperatures 80 degrees and higher Air spirals inward toward the center in an intense convection current

17 A tornado is a cyclonic storm with a very intense low-pressure center. Tornadoes are short-lived and local in extent, but they can be extremely violent. They typically follow a very narrow, sharply defined path, usually in the range of m wide.

18 Tornadoes Derivation--probably derived from the spanish word "tronada" meaning thunderstorm

19 Origin - -usually associated with severe thunderstorms -quickly advancing cool air is undercut by warmer moist air - warmer air rises -updraft formed from rising air releases more heat by condensing water vapor -Conservation of angular momentum causes speed of spin to increase -hot moist air continues to fuel this

20 structure - -tornado proper, area inside tornados of low pressure and 5-15 miles in diameter -winds of approximately 150 mph or less -however, vacuum effect caused by poor ventilation infers speeds of approx. 500 mph -buildings implode due to vacuum and poor ventilation -classified on the Fujita-Pearson scale -ranking with combination of maximum wind speeds, path length, and path width

21 Structure - -tornado proper, area inside tornado of low pressure and 5-15 miles in diameter. -winds of approximately 150 mph or less -however, vacuum effect caused by poor ventilation infers speeds of approx. 500 mph -buildings implode due to vacuum and poor ventilation -classified on the Fujita-Pearson scale - ranking with combination of maximum wind speeds, path length, and path width.

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24 Fujita defined downbursts as a surface wind in excess of 34 knots caused by a small-scale downdrift from the base of a convective cloud. He further subdivided downbursts into two categories "macrobursts" and "microbursts": Macroburst- greater than 2 1/2 miles wide at the surface, duration of 5-30 minutes with winds up to 117 miles per hour. Microburst- less than 2 1/2 miles wide at the surface, duration less than 5 minutes and winds up to 146 miles per hour.

25 Causes of Thunderstorms: Thunderstorm - a local storm produced by a cumulonimbus cloud, always with lightning and thunder, and usually accompanied by strong gusts of wind, heavy rain, and sometimes hail. Thunder - the sound that follows a flash of lightning. It is caused by sudden expansion of the air in the path of the electrical discharge

26 Storm - a disturbance of the atmosphere marked by wind and usually by rain, snow, hail, sleet, or thunder and lightning Lightning - any visible electrical discharg produced by thunderstorms Cloud - a visible mass of minute water and/or ice particles in the atmosphere suspended above the earth's surface.

27 Classification of Clouds: Following the classification of clouds originally proposed by Luke Howard, there are three main types of clouds: cirrus, stratus, and cumulus. Cirrus clouds are wispy. curly, or stringy They usually signal fair weather ahead. Stratus clouds are stratified, or layered, often blanketing the entire sky with a uniform cover. Cumulus clouds are lumpy or heaped. The weather they bring depends on their height and size

28 The Nature of Lighting

29 Basic Sequence in Creating a Lightning Bolt (as observed through high speed photography)

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