Bài giảng khí hậu học chương 1

G304 – Physical Meteorology and Climatology Chapter Composition and Structure of the Atmosphere By Vu Thanh Hang, Department of Meteorology, HUS The Atmosphere, Weather and Climate • The atmosphere: a mixture of gas molecules, microscopically small suspended particles of solid and liquid, falling precipitation; a complex fluid system  generates the chaotic motion  weather • Weather: state of the current atmosphere in lower levels with time scales from minutes to hours (shortterm phenomena) • Climate: long-term patterns of weather with time scales from months to centuries 1.1 Thickness of the Atmosphere • The atmosphere has no distinct upper boundary • The air becomes less and less dense with increasing altitude • At 16km, the air density is only ~10% and at 50km it is ~1% of that at sea level • In fact, 99.99997% of the atmosphere below 100km • However, it can reach to an altitude of 20.000km according to satellite observations • Compare with the 6500km radius of Earth 1.2 Composition of the Atmosphere • A mixture of invisible gases and suspended microscopic solid particles and water droplets • Molecules of the gases can be exchanged between the atmosphere and Earth’s surface by physical processes; also be produced and destroyed by chemical reactions between gases • The gas concentration in the reservoir (atmosphere) will remain constant so long as the input rate (gas moves from ground to atmos.) is equal to the output rate (gas moves from atmos to ground)  the concentration of the gas exists in a steady state 1.2 Composition of the Atmosphere (cont.) • Individual molecules stay in the atmosphere for only a finite period of time  residence time • The residence time is found by dividing the mass of the substance in the atmosphere (in kilograms) by the rate at which the substance enters and exits the atmosphere (in kilograms per year) • Atmospheric gases are often categorized as being permanent or variable, depending on whether their Fig 1.2 (a) long residence time; concentration is stable (b) short residence time 1.2 Composition of the Atmosphere (cont.) • Permanent gases form a constant proportion of the atmos Mass (99.999%) • Nitrogen (N2): - has a very long residence time, 42 million years due to the processes that add and remove nitrogen from the atmosphere occur very slowly - has little effect on most meteorological and climatological processes • Oxygen (O2): - is crucial to the existence of virtually all forms of life - residence time is about 5000 years 1.2 Composition of the Atmosphere (cont.) Permanent gases of the atmosphere Permanent gases occur in a constant proportion throughout the atmosphere’s lowest 80km  homosphere 1.2 Composition of the Atmosphere (cont.) • Variable gases are those whose distribution atmosphere varies in both time and space in the • Despite their relative scarcity, some of these gases affect the behavior of the atmosphere • Heterosphere, where lighter gases become increasingly dominant with increasing altitude Variable gases of the atmosphere 1.2 Composition of the Atmosphere (cont.) • Water vapor: - decreases rapidly with altitude, is found in the lowest 5km of the atmosphere - is related to hydrologic cycle - changes phase into liquid and solid forms at Earth’s surface and in the atmosphere - has a very short residence time of only 10 days - higher in the tropics - the source of moisture needed to form clouds - a very effective absorber of energy emitted by Earth’s surface - a greenhouse gas 1.2 Composition of the Atmosphere (cont.) Water cycle 1.2 Composition of the Atmosphere (cont.) • Ozone: - is the form of oxygen in which three O atoms are joined to form a single molecule - exists in the upper atmosphere - is a major component of air pollution, causing irritation to lungs and eyes and damage to vegetation near Earth’s surface - O3 in the upper atmosphere is vital to life on Earth because it absorbs lethal ultraviolet radiation from the Sun - is continually being broken down and re-formed to yield a relatively constant concentration in the O3 layer 1.2 Composition of the Atmosphere (cont.) 1.2 Composition of the Atmosphere (cont.) • Aerosols: - are small solid particles and liquid droplets in the air (excluding cloud droplets and precipitation) - are formed by both human and natural processes - reduce visibility - play a major role in the formation of cloud droplets (condensation nuclei) - have life spans of a few days to several weeks - are removed effectively by falling precipitation 1.3 Vertical structure of the Atmosphere • Atmospheric structure refers to the state of the air at different heights • The true vertical structure of the atmosphere varies with time and location due to changing weather conditions and solar activity • Standard atmosphere: is an idealized, dry, steady-state approximation of the atmospheric state as a function of height • Devided into layers based on how mean temperature varies with altitude • Four layers are: troposphere, stratosphere, mesosphere, thermosphere 1.3 Vertical structure of the Atmosphere (cont.) - Troposphere: 0≤H ≤11km - Stratosphere: 11 ≤H ≤47km - Mesosphere: 47 ≤H ≤84.9km - Thermosphere: 84.9km ≤H Temperature profile of the atmosphere 1.3 Vertical structure of the Atmosphere (cont.) • The troposphere: - is the lowest of the four temperature layers - is where the vast majority of weather events occur - temperature decreases with height - vertical mixing and turbulence - contains 80% of the atmosphere’s mass - the depth varies from 8km (in polar regions) to 16km (in tropics) - the average global temperature is ~15oC near the ground but only ~-57oC at the top of troposphere (an average decrease of ~6.5oC/km) - a transition zone called tropopause 1.3 Vertical structure of the Atmosphere (cont.) • The stratosphere: - Little weather occurs - In the lowest part, the temperature remains relatively constant up to about 20 km - From there to the stratopause, the temperature increases with altitude  the result of UV radiation being absorbed by ozone - contains about 19.9% of the total mass of the atmosphere - Ozone layer (20-30km) is a zone of increased ozone concentration - O3 absorbs the solar energy  warms the stratosphere, protects life on Earth from lethal effects of UV radiation 1.3 Vertical structure of the Atmosphere (cont.) • The mesosphere: - Temperature decreases with altitude - The absortion of solar radiation near the base of the mesosphere provides most of the heat for the layer • The thermosphere: - Temperature increases with altitude - The atmosphere is so sparse  a gas molecule will normally move several kilometers before colliding with another 1.3 Vertical structure of the Atmosphere (cont.) • The inosphere: - based on its electrical properties extends from the upper mesosphere into the thermosphere, contains electrically charged particles (ions) - is important for reflecting AM radio waves back toward Earth and is responsible for the aurora borealis and the aurora australis An aurora borealis Subatomic particles from the Sun are captured by Earth’s magnetic field, causing an agitation of molecules & the emission of light with different colors 1.4 Evolution of the Atmosphere • Earth was formed perhaps 4.5 billion years ago • If an atmosphere formed with Earth, it must have consisted of the gases most abundant in the early solar system including large amounts of hydrogen and helium • Today’s atmosphere composed mostly nitrogen & oxygen  where did the original gases go & how were they replaced? • If molecules move with sufficient speed, known as their escape velocity, they can overcome gravity and leave the atmosphere • Light gases are more likely to achieve escape velocity  the hydrogen and helium were most readily lost • Over time a new secondary atmosphere formed, gases released from Earth’s interior by volcanic eruptions - a process called outgassing 1.4 Evolution of the Atmosphere (cont.) • The gases spewed out during volcanic events are predominantly water vapor and carbon dioxide, with lesser amounts of sulfur dioxide, nitrogen, and other gases • The transformation to an atmosphere high in oxygen depended on the advent of primitive, anaerobic bacteria about 3.5 billion years ago • These primitive life-forms were the first in a long line of organisms that removed carbon dioxide from the air and replaced it with oxygen • Ultimately, plant and later animal material sank to the ocean floor, where the organic carbon was locked away in sediments 1.5 Some weather basis • Pressure (mb ~ hPa) • Air tends to blow away from regions of high pressure toward areas of lower pressure  winds • Air tends to rise in areas of low surface pressure and sink in zones of high pressure • Rising motions favor the formation of clouds, while sinking motions promote clear skies • Atmospheric pressure is routinely plotted on maps by the use of lines called isobars which connects points having equal air pressure 1.5 Some weather basis (cont.) A surface weather map 1.5 Some weather basis (cont.) • Wind speed and direction can be obtained on weather maps by looking at the station models, which contain symbols and numbers giving weather information for particular locations Station model symbols 1.5 Some weather basis (cont.) • Temperature varies from place to place • Major changes in temperature often occur due to the presence of fronts, fairly narrow boundary zones separating relatively warm and cold air • Cold fronts are shown as a blue line with triangles while warm fronts are depicted by a red line with semicircles • Relative humidity expresses the amount of water vapor in the air [...]... temperature varies with altitude • Four layers are: troposphere, stratosphere, mesosphere, thermosphere 1. 3 Vertical structure of the Atmosphere (cont.) - Troposphere: 0≤H 11 km - Stratosphere: 11 ≤H ≤47km - Mesosphere: 47 ≤H ≤84.9km - Thermosphere: 84.9km ≤H Temperature profile of the atmosphere 1. 3 Vertical structure of the Atmosphere (cont.) • The troposphere: - is the lowest of the four temperature... concentration - has a residence time of about 15 0 years 1. 2 Composition of the Atmosphere (cont.) 1. 2 Composition of the Atmosphere (cont.) 1. 2 Composition of the Atmosphere (cont.) The data are obtained from the Mauna Loa Observatory, with the zigzag line showing the seasonal cycle in the growth and decay of plants The concentration of CO2 has increased at a rate of ~1. 8 ppm per year, because of anthropogenic... and turbulence - contains 80% of the atmosphere’s mass - the depth varies from 8km (in polar regions) to 16 km (in tropics) - the average global temperature is ~15 oC near the ground but only ~-57oC at the top of troposphere (an average decrease of ~6.5oC/km) - a transition zone called tropopause 1. 3 Vertical structure of the Atmosphere (cont.) • The stratosphere: - Little weather occurs - In the lowest... called isobars which connects points having equal air pressure 1. 5 Some weather basis (cont.) A surface weather map 1. 5 Some weather basis (cont.) • Wind speed and direction can be obtained on weather maps by looking at the station models, which contain symbols and numbers giving weather information for particular locations Station model symbols 1. 5 Some weather basis (cont.) • Temperature varies from place.. .1. 2 Composition of the Atmosphere (cont.) The distribution of water vapor 1. 2 Composition of the Atmosphere (cont.) • Carbon dioxide: - is supplied to the atmosphere by plant and animal respiration, the decay of organic material, volcanic... growth and decay of plants The concentration of CO2 has increased at a rate of ~1. 8 ppm per year, because of anthropogenic combustion and deforestation of large tracts of woodland 1. 2 Composition of the Atmosphere (cont.) 1. 2 Composition of the Atmosphere (cont.) • Ozone: - is the form of oxygen in which three O atoms are joined to form a single molecule - exists in the upper atmosphere - is a major... increases with altitude  the result of UV radiation being absorbed by ozone - contains about 19 .9% of the total mass of the atmosphere - Ozone layer (20-30km) is a zone of increased ozone concentration - O3 absorbs the solar energy  warms the stratosphere, protects life on Earth from lethal effects of UV radiation 1. 3 Vertical structure of the Atmosphere (cont.) • The mesosphere: - Temperature decreases... on Earth because it absorbs lethal ultraviolet radiation from the Sun - is continually being broken down and re-formed to yield a relatively constant concentration in the O3 layer 1. 2 Composition of the Atmosphere (cont.) 1. 2 Composition of the Atmosphere (cont.) • Aerosols: - are small solid particles and liquid droplets in the air (excluding cloud droplets and precipitation) - are formed by both human... of the heat for the layer • The thermosphere: - Temperature increases with altitude - The atmosphere is so sparse  a gas molecule will normally move several kilometers before colliding with another 1. 3 Vertical structure of the Atmosphere (cont.) • The inosphere: - based on its electrical properties extends from the upper mesosphere into the thermosphere, contains electrically charged particles (ions)... borealis and the aurora australis An aurora borealis Subatomic particles from the Sun are captured by Earth’s magnetic field, causing an agitation of molecules & the emission of light with different colors 1. 4 Evolution of the Atmosphere • Earth was formed perhaps 4.5 billion years ago • If an atmosphere formed with Earth, it must have consisted of the gases most abundant in the early solar system including