NAS 125: Meteorology The Atmosphere. Rev. 19 January 2006The Atmosphere2 North African dust, part 1...

NAS 125: Meteorology

The Atmosphere

Rev. 19 January 2006 The Atmosphere 2

North African dust, part 1

• For years, scientists had suspected that much of the red iron- and clay-rich soils on islands throughout the Caribbean and in Bermuda originated in North Africa, but were blown West by the Northeast trade winds.

• They also suspected that dust from North Africa fertilized the tropical rain forests of the Amazon basin.

• The transatlantic transport of African dust was confirmed by satellite data.



• North African dust lowers North American air quality, primarily over the southeastern United States.

• It may contribute to development of red tides in the Gulf of Mexico, and may threaten coral reefs in the Caribbean.

• Winds whipped up by winter disturbances over North Africa pick up dust from the soil surface and transport it as high as 3,000 m.



• The Northeast trade winds pick up the finer particles and transport them across the Atlantic to the Caribbean, Central America, and the southeastern U.S.– Florida receives more than half of the North African dust

transported to the United States.

• The transatlantic crossing takes one to two weeks, with most of the transport occurring from June to October – with a peak in July.

• African droughts may increase dust transport.



• North African dust is part of the reason for reddish haze and colorful sunsets over the Southeast.

• It may shelter pathogens and transport them across the Atlantic.– Even without pathogens, dust may trigger allergic and

respiratory reactions.

• North African dust may supply nutrients to the Gulf of Mexico, which has the unfortunate effect of making algae blooms and red tides more likely.– Algae and phytoplankton growth may harm Caribbean

corals.


Environmental spheres

• Earth’s surface is a complex interface where four spheres meet, overlap, and interact. These spheres provide important organizing concepts for the systematic study of Earth’s environments:– Lithosphere (the solid, inorganic portion)

– Hydrosphere (water in all its forms) Biosphere (life and the places where it can exist)

– Biosphere (life and the places where it can exist)

– Atmosphere (the gaseous envelope that surrounds Earth)


Importance of weather

• Weather affects virtually all aspects of our lives, from recreation to economic activities:– Effects on energy and food prices affect all aspects of the

economy.

– Adverse weather can kill or lead to increased incidence of disease.

– Weather can disrupt transportation networks.

– Weather can affect recreational activities.

• Weather is variable.


The Atmosphere

• The Earth is unique because of the composition of its atmosphere, which makes life possible.– It supplies the oxygen that all but a handful of organisms

need to survive.

– It supplies the carbon dioxide that photosynthetic plants and animals use to make the carbon-based compounds required for living things.

– It maintains the water supply for life.

– It moderates the climate against temperature extremes.

– It protects Earth from the Sun’s ultraviolet radiation.


Extent of atmosphere, part 1

• The atmosphere extends outward to 10,000 kilometers.

• Most of its mass is concentrated at low elevations.– More than half of the atmosphere’s mass is concentrated in

the lowest 5,500 m.

– More than 99 percent of the atmosphere’s mass is concentrated below 32 km.

• Atmosphere fills empty spaces in rocks and soil, such as caves and crevices.


Extent of atmosphere, part 2

• Gases are dissolved in the waters of the Earth as well as in the bodily and cellular fluids of living organisms.


Weather

• Weather is the instantaneous state of the atmosphere at a given place and time.– Weather may be described in terms of variables such as

temperature, humidity, cloudiness, precipitation, and wind speed and direction.

– Weather varies continuously from place to place and time to time.

• “If you don’t like the weather, wait a minute.”

– Meteorology is the study of the atmosphere and the processes that cause weather.


Climate, part 1

• Climate refers to the pattern or average of weather conditions over a long period, encompassing mean characteristics, variability, and extremes.– By international convention, climate variables are averaged

over a 30-year period beginning with the first year of a decade (e.g., 1971-2000). The averaging period is shifted forward 10 years with the beginning of a new decade.

– These 30-year averages (normals) of monthly temperature and precipitation variables are used to describe climate.

• Seasonal variables, length of growing season, percent of possible sunshine, and number of days with dense fog among other important variables.


Climate, part 2

• Climate is probably the most important environmental control, affecting agriculture, water supply, heating and cooling requirements for buildings, weathering and erosion processes, and much, much more.

• Climatology is the study of climate, its controls, and its spatial and temporal variability.


Evolution of the atmosphere

• The origins of the atmosphere began with the Earth’s genesis about 4.6 billion years ago.– Evidence for the evolution of the atmosphere can be found

in meteorites, rocks, and fossils.

• Primeval phase– The primeval phase covers the origins of the Earth, its

atmosphere, and the early development of the atmosphere.


Nebular hypothesis, part 1

• About 5 or 6 billion years ago, the solar nebula, a disc-shaped interstellar cloud – mainly consisting of hydrogen, helium, oxygen, nitrogen, silicon, calcium, aluminum, sodium, potassium, magnesium, carbon, sulfur, iron and some heavy metals – rotated through our region of the Milky Way.



• Gravity forced more matter to concentrate near the center of the disc, as it did so, pressure and temperature inside the proto-sun would increase until self-sustaining fusion reactions started.

• The spin of the solar nebula induced eddies in the gas and dust.

• Planetismal bodies formed from matter concentrating in the center of the eddies.



• Moons formed around the protoplanets in secondary eddies.

• Protoplanets gained additional moons by capturing asteroids.

• The 9 or 10 protoplanets grew larger by sweeping up more material from the cloud of gas and dust.



• Initially, the composition of the protoplanets was similar, although heavier elements were more abundant among the inner planets than the outer ones.

• Heavier elements concentrated near the protoplanets’ cores.



• The four inner planets (Mercury, Venus, Earth and Mars) lost more of their light elements (hydrogen and helium) than the larger, cooler gaseous planets that were farther from the Sun.

• Solar wind swept the inner part of the solar system of lighter material.


Earth ‘garden’

• Earth would gain much of its elements compounds from the gas cloud it condensed from.

• More would come in from the rain of comets and asteroids in the Earth’s early history – this rain of organic compounds may have planted the seed for the development of life as well as the atmosphere.


Early Earth, part 1

• The early Earth would have been hot as a result of gravitational compaction, radioactivity and asteroid impacts.

• The core and mantle formed by about 4.5 billion years ago.

• A thin primeval atmosphere would have been established by about 4.4 billion years ago.– The early atmosphere was probably composed of molecular

hydrogen (H2), helium (He), methane (CH4), and ammonia (NH3).


Early Earth, part 2

• Heat in the inner Earth drives volcanic and tectonic processes; volcanic outgassing was probably the primary source of atmospheric gases.– About 85 percent of outgassing took place within the first

million years of the Earth’s existence.

– Outgassing produced an atmosphere that was primarily carbon dioxide (CO2), nitrogen (N2), and water vapor (H2O), with trace amounts of methane, ammonia, sulfur dioxide (SO2), and hydrochloric acid (HCl).


Early Earth, part 3

• Radioactive decay of potassium-40 added argon (Ar), an inert gas, to the atmosphere.

• Dissociation of water vapor by ultraviolet radiation added free oxygen (O2) to the atmosphere.– Much of the molecular hydrogen, a light gas, escaped to

space because the Earth’s gravity was not strong enough to retain it in the atmosphere.

– Some of the oxygen combined with other elements.


Early Earth, part 4

• Some scientists believe that, between 4.5 and 2.5 billion years ago, the Sun was 30 percent fainter than it is today, but the CO2-rich atmosphere was both 10 to 20 times denser than it is today, and it was a potent greenhouse environment.– Surface temperatures ranged as high as 85 C and 110 C.


Early Earth, part 5

• By about 4 billion years ago, the Earth cooled enough to allow a stable crust to form and chemical compounds such as water to remain stable.– Atmospheric water vapor condensed to form clouds, and

torrential rains filled the ocean basins such that the oceans covered 95 percent of the planet.

– Carbon dioxide gas dissolved into the surface waters, forming carbonic acid, an important agent for the chemical weathering of rock at or near the surface of the Earth.


Early Earth, part 6

• Early life transformed the atmosphere.– By about 2.5 billion years ago, cyanobacteria (blue-green

algae) filled the primitive oceans. They manufactured their own organic nutrients from carbon dioxide and water in a chemical reaction, photosynthesis, powered by the energy of sunlight.

– Oxygen (O2) is a by-product of photosynthesis.

– As life became more abundant, the atmosphere became depleted in carbon dioxide and enriched in oxygen.


Early Earth, part 7

• Early life (continued):– Little change in atmospheric oxygen occurred for about

500 million years, however, as the oxygen first combined with minerals in ocean sediments.

– As the surface sediments became saturated with respect to their ability to bind oxygen, oxygen concentrations in the atmosphere began to rise.

• Nitrogen, a product of outgassing, became the most abundant atmospheric gas.

• As oxygen levels rose, an ozone (O3) layer formed that protected life from the Sun’s ultraviolet radiation.


Early Earth, part 8

• Carbon dioxide levels have fluctuated considerably, leading to extended periods of greenhouse warming as well as extended ice ages.– Carbon dioxide vented by outgassing during period of

extended volcanic activity 120 to 100 million years ago led to extended warm period, with temperatures as much as 10 C warmer than today.

– During Pleistocence ice ages (1.7 million years ago to 10,500 years ago) carbon dioxide levels decreased as glaciers advanced and increased as glaciers retreated.


Modern atmosphere, part 1

• The principal gases of atmosphere have a uniform vertical distribution in the lowest 80 km. This portion of the atmosphere is called the homosphere.

• Above 80 km, the composition of the atmosphere is stratified such that the concentration of heavier gases decreases more rapidly than that of the lighter gases. This portion is called the heterosphere.


Gases of the Atmosphere

• Basic composition of the atmosphere:– Nitrogen – 78%

– Oxygen – 21%

– Argon – nearly 1%

– Neon, helium, methane, krypton, hydrogen, water vapor, carbon dioxide, ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, and various hydrocarbons – trace amounts


Other planets

• Earth’s nitrogen/oxygen dominated atmosphere is strikingly different from the carbon dioxide-rich atmosphere of Venus and Mars.– The Venutian atmosphere is 100 times more dense than

that of Earth, with a surface temperature of about 460 C.– The Martian atmosphere is much thinner than Earth, with

surface temperatures ranging from about -60 C at the equator to less than –120 C at the poles.


Role of H2O, CO2, and ozone

• While occuring in trace amounts, water vapor (H2O), carbon dioxide (CO2), and ozone (O3) are essential for life.– Water vapor determines the humidity of the atmosphere, is

the source of all clouds and precipitation, and is intimately involved in the storage, movement, and release of heat energy.

– Water vapor and atmospheric CO2 significantly affect the climate because they can absorb infrared radiation, keeping the lower atmosphere warm enough for life.

– Ozone shields life from harmful effects of ultraviolet light.


Aerosols, part 1

• Aerosols are minute liquid and solid particles found in the atmosphere.

• They are typically invisible, but larger aggregates, such as water or ice droplets in clouds, can be seen.

• Most are found at lower levels in the atmosphere.• They come from both natural and human-made

sources.


Aerosols, part 2

• Aerosols affect the weather and climate in two ways:– Many are hygroscopic (absorb water), and water vapor

collects around them, which contributes to cloud formation;

– Aerosols can either absorb or reflect sunlight, thus decreasing the amount of solar energy that reaches Earth’s surface.


Discovery science

• Discovery science describes natural structures and processes as accurately as possible through careful observation and analysis of data.

• Data are recorded observations which can be either quantitative or qualitative.

• Discovery science may lead to important conclusions via inductive reasoning, in which scientists derive generalizations based on a large number of specific observations.


Hypothesis-based science

• Hypothesis-based science is a process of inquiry that asks specific questions

• Usually involves the proposing and testing of hypothetical explanations, or hypotheses, via the scientific method.


Discovery of the ozone hole, part 1

• Scientists of the British Antarctic Survey first noticed a decline in the amount of stratospheric ozone during the (Southern Hemisphere) spring of 1985.

• A region almost as large as North America was affected.

• Record searches revealed evidence of ozone depletion in each of the previous eight years.



• The BAS findings were initially dismissed as the result of instrument error.

• Others argued that the ozone hole was real, but a normal phenomenon produced by the polar atmospheric circulation.

• A third group argued that the ozone hole was caused by pollution.



• A massive field study was launched in 1987 to settle the matter.– The scientists used satellites, aircraft, and balloons

equipped with special instruments to collect atmospheric data.

– The first finding was that the ozone hole was real.

– The second finding was that high levels of chlorine monoxide (ClO) were present, a chemical that is known from laboratory studies to damage ozone.

– Chlorine monoxide is a by-product of chlorofluorocarbons.


Steps in the scientific method

• The scientific method is a formal set of rules for forming and testing hypotheses.

• Steps in the scientific method:– Observation

– Question

– Hypothesis

– Prediction

– Test


Hypotheses

• A hypothesis is an informed guess about the way a process works that enables a scientist to predict what will happen in different situations.

• Hypotheses– Are possible explanations

– Are based on past experience

– Are valuable only if testable and falsifiable

– Can be proven wrong, but can never be proven right


Theory

• A system of statements and ideas that explains a group of related facts or phenomena.

• Hypotheses developed from a theory consistently resist scientists’ efforts to disprove them.


Experiment

• A way of testing a hypothesis or of searching for some unknown effect.

• Proper experimental design is essential for the success of any experiment and must take into account the following:– The population of interest

– Statistics to be used to analyze the data

– Statistically representative samples of the population

– Experimental treatment(s) and control(s)


Atmospheric models, part 1

• Models are often used in the effort to better understand weather and climate processes.

• A scientific model is an approximation or simulation of a real-world system.– A system is an entity that has components that function and

interact in an orderly and predictable manner that can be described by fundamental physical principles.

– The Earth-atmosphere system is comprised of the Earth’s surface features, plus that of the atmosphere.



• Models include only the essential elements (or elements perceived to be essential) of a system.– Construction of a model often helps scientists determine

which elements are essential or not.

– The simplicity of a model can help scientists gain important insights into how a system works.

– Models can also be used to predict how a system might respond to changes.



• Models may be classified as conceptual, graphical, physical, or numerical.– A conceptual model is an abstract idea that represents some

fundamental law or relationship.

– A graphical model compiles and display data in a manner that readily conveys meaning (“A picture is worth a thousand words.”).

– A physical model is a miniaturized version of a system.• An salt water aquarium is a miniaturized version of a coral reef.

– A numerical model consists of one or more equations that describe the relationship among variables in a system.



• All models simulate reality.– A weather map portrays the state of the atmosphere at a

given time.• Weather maps integrate observations from weather stations that

may be hundreds of kilometers apart.

– Weather satellites offer a more complete field of view, but the spatial resolution of the satellites is limited.

– The predictions of numerical models may not be accurate since we cannot model everything relevant to weather processes.


Numerical models

• Numerical models have been used to forecast weather since the 1950s.

• Numerical models are extensively used to predict the effects of increasing atmospheric carbon dioxide on global climate.


Atmospheric CO2

• Human activities may be causing climate change by increasing carbon dioxide concentration in the atmosphere.– Since the Industrial Revolution, the concentration of CO2 in

the atmosphere has increased greatly as a result of burning fossil fuels.

• Measurements in 1958 read 316 ppm and have increased to 370 ppm today.


Greenhouse effect

• Rising levels of atmospheric CO2 may have an impact on Earth’s heat budget.

• When light energy hits the Earth, much of it is reflected off the surface.– CO2 causes the Earth to retain some of the energy that

would ordinarily escape the atmosphere.• This phenomenon is called the greenhouse effect.

• The Earth needs this heat, but too much could be disastrous.


Global warming

• Scientists continue to construct models to predict how increasing levels of CO2 in the atmosphere will affect Earth.– Several studies predict a doubling of CO2 in the atmosphere

will cause a 2º C increase in the average temperature of Earth.

– Rising temperatures could cause polar ice cap melting, which could flood coastal areas.

• It is important that humans attempt to stabilize their use of fossil fuels.


Global climate model building

1. Design a global climate model (GCM) that encompasses several controls of climate and that accurately predicts long-term averages for sites worldwide.

2. Hold all other climate variables constant while varying CO2 levels. Note the effects.

3. Subtract the present temperature pattern from the predicted pattern to determine the magnitude of the predicted change.


Atmospheric monitoring, part 1

• Most of what we know about the atmosphere is derived from direct observation and remote sensing.

• Surface observations– Early observations were either qualitative assessments or

measurements made by primitive instruments and were written down in journals or diaries.

– First systematic observations in North America were recorded by John Campanius Holm at Old Swedes Fort near what is now Wilmington, Del., from 1644-1645.

– Temperature records date from 1731 in Philadelphia; 1738 in Charleston, S.C.; and 1753 in Cambridge, Mass.



• Surface observations (continued)– The oldest continuous series of weather observations began

in 1781 in New Haven, Conn.

– Thomas Jefferson (at Monticello) and the Rev. James Madison (at the College of William and Mary) began the first series of simultaneous weather observation over a six-year period beginning in 1778.

– James Tilton, the surgeon general of the United States, made the first step in establishing a series of weather stations across the United States by ordering the Army Medical Corps to record conditions at Army posts.



• Surface observations (continued)– Tilton’s successor, Joseph Lovell, in 1818 issued

instructions for taking weather observations that standardized the process.

– Lovell began compiling the reports, summarizing, and publishing the weather data in 1826.

– Joseph Henry, the first secretary of the Smithsonian Institution, established a national network of volunteer observers and in 1849 persuaded telegraph companies to allow their telegraphers to record and transmit weather data to Washington, D.C.



• Surface observations (continued)– Henry published the first daily weather maps in 1850.

– In the 1860s, concern over shipping losses due to weather on the Great Lakes lead to the establishment of a storm-warning network operated by the U.S. Army Signal Corps. The network began operating on 1 November 1870.

– The network was expanded nationwide in 1872, and was transferred to civilian hands – as a Weather Bureau of the U.S. Department of Agriculture – in 1891.



• Surface observations (continued)– Because of concerns for aviation safety, the Weather

Bureau was transferred to the Department of Commerce on 1 July 1940.

– The Weather Bureau was reorganized as the National Weather Service (NWS) in 1965, first under the Environmental Science Services Administration (ESSA), then under the National Oceanic and Atmospheric Administration (NOAA) in 1871.

– The National Weather Service underwent a massing reorganization and modernization during the 1990s.



• Surface observations (continued)– As a result of the modernization, 1700 automated weather

stations replaced the largely human observer network. The automated network is called the Automated Surface Observing System (ASOS).

– Volunteers make up the NWS Cooperative Observer Network, which, with its 8,000 stations, supplements ASOS.


Upper-air observations, part 1

• Kites were used beginning in the 1700s in early investigations of the upper atmosphere.– Alexander Wilson, in 1749, obtained the first free-air

temperature profile of the lower atmosphere.

– Benjamin Franklin used a kite to demonstrate the nature of lightning on 10 June 1752. His observations led to his invention of the lightning rod.

– On 4 August 1894, kites carrying self-recording thermometers, or thermographs, were used at Harvard’s Blue Hill Observatory near Boston, Mass., providing a temperature profile to an altitude of 427 m



• Kites (continued)– The Weather Bureau operated a kite network from 1907

until 1933, when longest-operating kite station – at Ellendale, N.D. – was closed. The kites carried a special instrument, a meteorograph, that recorded air pressure, temperature, humidity, and wind speed up to a maximum altitude of about 3,000 m.

• In 1804, J.L. Gay Lussac and Jean Biot made the first balloon-based measurements of atmospheric conditions aloft, once reaching an altitude of 7,000 m.



• Balloons (continued)– James Glaisher and Henry Coxwell made a series of

balloon ascents in 1862, once nearly perishing from oxygen deprivation and hypothermia while setting an altitude record of 9,000 m.

– In the 1920s, the radiosonde was developed for balloon-based observations.

• The radiosonde, equipped with a radio transmitter, transmits altitude readings (soundings) of temperature, air pressure, and dewpoint to a surface station.



• Balloons (continued)– Radiosonde (continued)

• A rawinsonde is a radiosonde whose movements are tracked by ground stations in order to monitor changes in wind direction and speed aloft.

• Radiosondes are launched simultaneously at 0000Z and 1200Z from hundreds of weather stations around the world.

• Radiosonde balloons burst at altitudes of about 30,000 m and the instrument package descends to the surface under a parachute. About 20 percent of the radiosondes in the United States are recovered, refurbished, and reused.



• Aircraft have been used for weather observations since the early 20th century.– The Weather Bureau used to use aircraft to make upper-air

observations to altitudes of about 4,900 m, but discontinued the practice at the time because of the cost and danger of aircraft operation.

– Aircraft, such as the Hurricane Hunters, are used routinely today.

• Some aircraft drop dropwinsondes – similar to radiosondes – especially over oceans where it is impossible to consistenly launch radiosondes.



• Robert H. Goddard in 1929 became the first to use rockets to make upper-air observations.– The use of rockets became common after World War II.

– Rockets were first used to launch satellites with Sputnik I on 4 October 1957.

– The first weather satellite, TIROS-1 (Television and Infrared Observation Satellite), was launched by the United States on 1 April 1960.

– Weather satellites are invaluable for weather observation and storm surveillance, and cover areas lacking ground stations.


Vertical structure

• Trailing bits first:– “–sphere” is used when talking about the entire layer;

– When referring to just the upper portion of a layer or the boundary between two layers, “-pause” is used.

• One way to define layers in the atmosphere is on the bases of temperature trends. There are five thermal layers in the atmosphere: troposphere. stratosphere, mesosphere, thermosphere, and exosphere.


Thermal layers, part 1

• Temperature alternately decreases and increases from one layer to the next.

• The thermal layers:– The troposphere is the lowest thermal layer of the

atmosphere, in which temperature decreases with height. Most weather phenomena occur in the troposphere.

• Temperature drops about 6.5 C for every 1,000 m increase in elevation.

• Height of the troposphere varies with time and place.

– The tropopause is a transition zone above the troposphere where temperatures no longer decrease with height.



• The thermal layers (continued):– The stratosphere is the atmospheric layer directly above

troposphere, where temperature increases with height.

– The stratopause is the top of the stratosphere, elevation about 48 kilometers, were maximum temperature is reached.

– The mesosphere is the atmospheric layer above the stratopause, where temperature again decreases with height as it did in the troposphere, down to about -95.

– The mesopause is transition zone at the top of the mesosphere.



• The thermal layers (continued):– The thermosphere is the highest recognized thermal layer

in the atmosphere, above the mesopause, where temperature remains relatively uniform for several kilometers and then increases continually with height.

– The exosphere is the highest zone of Earth’s atmosphere.



• The warm zones of the thermal layers each have their own specific source of heat.– In the troposphere, it’s the visible portion of sunlight.

– In the stratosphere and thermosphere, the Sun’s ultraviolet rays serve as the heat source (the warm zone of the stratosphere is near the top of the ozone layer, which absorbs UV rays).


The ionosphere, part 1

• The ionosphere is the deep layer of ions, electrically charged molecules and atoms, in the middle and upper part of the mesosphere and the lower part of the thermosphere that boosts long-distance radio communication by reflecting radio waves back to Earth.– Radio waves propagate by bouncing back and forth

between the ionosphere and the Earth’s surface.



• The ionosphere also is where auroral displays originate.– The aurora borealis is in the Northern Hemisphere and the

aurora australis is in the Southern Hemisphere.

– Auroras often appear as shimmering waves of greenish-white light in the night sky.

– Auroral displays are generated by the solar wind – a “wind” of radioactive particles spreading out from the Sun at 400 to 500 km per second.



• Auroral displays (continued)– The Earth’s magnetic field is deformed as it deflects the

solar wind around the Earth.

– As the magnetosphere and solar wind interact, electrons collide with atoms and molecules in the ionosphere.

– The light is generated as the atoms and molecules recover from the collisions.

– Auroras are visible only at higher latitudes, and vary with solar activity.

NAS 125: Meteorology The Atmosphere. Rev. 19 January 2006The Atmosphere2 North African dust, part 1...

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