Introduction to atmospheric science

Introduction to Meteorology

Geronimo R. Rosario

Atmospheric science- is an umbrella term for the study of the atmosphere, its processes, the effects other systems [such as the oceans] have on the atmosphere, and the effects of the atmosphere on these other systems.

Major Subdivisions of Atmospheric Science◦ Atmospheric Physics ◦ Atmospheric Chemistry ◦ Atmospheric Dynamics ◦ Climatology ◦ Meteorology and Forecasting ◦ Extraterrestrial Planetary Atmospheric Science

Atmospheric Science

Atmospheric physics is the application of physics to the study of the atmosphere.

Atmospheric physicists attempt to model Earth’s atmosphere and the atmospheres of the other planets using fluid flow equations, chemical models, radiation balancing, and energy transfer processes in the atmosphere (as well as how these tie into other systems such as the oceans).

Atmospheric Chemistry- is a branch of atmospheric science in which the chemistry of the Earth’s atmosphere and that of other planets is studied.

It is a multidisciplinary field of research and draws on environmental chemistry, physics, meteorology, computer modelling, oceanography, geology and volcanology and other disciplines.

Atmospheric Science

Atmospheric Dynamics- involves observational and theoretical analysis of all motion systems of meteorological significance, including such diverse phenomena as thunderstorms, tornadoes, gravity waves, tropical hurricanes, extratropical cyclones, jet streams, and global-scale circulations.

Climatology- is the study of atmospheric changes (both long and short-term) that define average climates and their change over time, due to both natural and anthropogenic climate variability.

Atmospheric Science

Extraterrestrial Planetary Atmospheric Science – the study of the atmospheric processes of other planets.

Meteorology includes atmospheric chemistry and

atmospheric physics with a major focus on weather forecasting. It is the study of the state and processes of the atmosphere such as weather and climate and how changes in temperature, pressure, humidity and wind speed and direction take place.

Atmospheric Science

Major Branches of Meteorology Physical meteorology - deals with the physical aspects of the

atmosphere, such as the formation of clouds, rain, thunderstorms, and lightning. Physical meteorology also includes the study of visual events such as mirages, rainbows, and halos.

Dynamic meteorology - the study of the winds and the laws that govern atmospheric motion. Equations that describe atmospheric motions.

Synoptic meteorology - is the study and analysis of large weather systems that exist for more than one day. Weather forecasting is part of synoptic meteorology. Day-to-day weather and forecasting.

Meteorology

Major Branches of Meteorology

Agricultural meteorology - deals with weather and its relationship to crops and vegetation.

Climatology - is the study of a region’s average daily and seasonal weather events over a long period. Climate describes the average weather of a region.

Aeronomy- is the study of the upper atmosphere with emphasis on composition and interaction with solar radiation.

Meteorology

Branches of Meteorology according to spatial distance

Microscale Meteorology - the study of atmospheric phenomena about 1 km or less, smaller than mesoscale, including small and generally, thunderstorms, fleeting cloud "puffs" and other small cloud features.

Mesoscale Meteorology – the study of weather systems about 5 kilometers to several hundred kilometers, smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems, such as sea breezes, squall lines, and mesoscale convective complexes.

Sypnoptic Scale meteorology- is a horizontal length scale of the order of 1000 kilometres (about 620 miles) or more. The phenomena typically described by sypnoptic meteorology include events like extratropical cyclones, baroclinic troughs and ridges, frontal zones, and to some extent jet streams.

Meteorology

Weather and Climate

Weather – is the condition of the atmosphere at a particular place over a short period of time.◦ Weather can be described in terms of temperature,

precipitation (snow, rain & hail), wind speed and direction, visibility and cloud amounts.

Climate - refers to the weather pattern of a place over a long period, maybe 30 years or more, long enough to yield meaningful averages.

Weather and Climate

Ancient Times

3000 BC – The beginnings of meteorology can be traced back in India to 3000 B.C.E. Writings such as the Upanishads, contain serious discussion about the processes of cloud formation and rain and the seasonal cycles caused by the movement of earth round the sun.

600 BC – Thales, first Greek meteorologist who described water cycle.

400 BC – Democritus predicted changes in the weather. 400 BC – Hippocrates discussed weather in his treatise

Airs, Waters and Places. locations, seasons, winds and air. 350 BC – Aristotle writes Meteorologica.

History of Meteorology

350 BC -Theophrastus, a pupil of Aristotle, compiled a book on weather forecasting, called the Book of Signs.

250 BC - Archimedes studied the concepts of buoyancy and the hydrostatic principle. Important for convertive clouds formation (eg. cumulus)

240 B.C. - Eratosthenes a Greek Librarian calculated circumference of spherical Earth about 40,000 km. (Alexandria and Syene(Aswan))= 5,000 stadia distance. 1 stadia= 0.16 km) Alexandria -7.2o. Actual circumference of the earth is 40,032 km. Erastosthenes estimates was 40,000 km (very close!).

150 A.D. - Ptolemy of Egypt's modified the early works of Apollonius and Eudoxus and proposed the Geocentric model where the earth is at the center of the universe and all the planetary objects including the sun and moon orbit around it

25 AD - Pomponius Mela, Roman geographer formalized the climatic zone system.

80 AD – Wang Chong, dispelled the Chinese myth on rain ocming from heavens and stated that rain came from evopatrated water and condensed into clouds and precipitate into rain.


Middle Ages

1088 - Shen Hou, Chinese scientist, wrote vivid descriptions of torandaoes, rainbow and lightning.

1121 - Al Khazini, Muslim Scientist, studied hydrostatic balance

13th century- St. Albert the Great, described the spherical shape of rain which in effect produced the rainbow..

1267 -Roger Bacon, first to calculate the angular size of the rainbow. He stated that the rainbow summit can not appear higher than 42 degrees above the horizon.

1441 - Prince Munjong, invented the first standardized rain gauge

1450 – Alberti developed a swinging- plate anemometer


Middle Ages 1450- Nicolas Cryfts, described the first hair hygrometer 1488-Lichtenberger published the first version

ofhis Prognosticatio linking weather forecasting with astrology.

1494- Columbus experienced a tropical cyclone, leads to the first written European account of a hurricane.

1510 –Reynmann, published ″Wetterbüchlein Von warer erkanntnus des wetters″, a collection of weather lore.

1543- Nicolaus Copernicus, Polish astronomer, proposed the heliocentric model, where the sun is at the center of the universe and all the planets revolve around it. This was accepted after 1400 years of Ptolemaic geocentric system.


17th century

1607 –Galileo Galilei invented thermoscope , a thermometer

1611 – Kepler studied snow crystals 1643 - Toricelli invented the mercury barometer 1648 - Pascal discussed atmospheric pressure

decreasing with height 1654 –De Medici, established weather observing

network 1662 - Sir Christopher Wren invented the

mechanical, self-emptying, tipping bucket rain gauge


17th Century

1660 - Robert Boyle discovered the relationship between pressure and volume of a gas.

1667 – Robert Hooke built pressure-plate anemometer.

1686 –Edmund Halley studied trade winds and monsoons

1687- Isaac Newton, English physicist, his laws of motions, cooling and refraction theories, had helped in the advancement of meteorology.


18th century

1716 - Edmund Halley suggested that aurorae are cuased by "magnetic effluvia”

1724 - Gabriel Fahrenheit introduced Fahrenheit scale in measuring temperature

1735 – George Hadley studied trade winds 1738 – Bernoulli published Hydrodynamics, initiating the kinetic

theory of gases. 1742 – Anders Celsius introduced Celsius scale (centigrade) 1743 - Benjamin Franklin asserted that cyclones move in a contrary

manner to the winds at their periphery. 1752- Benjamin Franklin demonstrated the electrical nature of

lightning. 1761 - Joseph Black discovered that ice absorbs heat without

changing its temperature when melting.


18th century

1772 - Black's student Daniel Rutherford discovered nitrogen 1774 - Louis Cotte was in charge of a "medico-meteorological"

network of French veterinarians and country doctors to investigate the relationship between plague and weather

1777 – Lavosier discovered oxygen and developed an explanation for combustion. Laid the foundations of chemistry

1780 - Theodor chartered the first international network of meteorological observers known as "Societas Meteorologica Palatina".

1783 – De Saussure demonstrated the first hair hygrometer (humidity)


19th Century

1801- Jacques Charles described the relationship between temperature and the volume of air

1802- Jean-Baptiste Lamarck first to classify clouds 1802-1803 – Luke Howard modified the clouds classification

with Latin names 1806 - Beaufort developed system for classifying wind speed 1810 - Sir John Leslie froze water to ice artificially. 1817 - von Humboldt published the first global climate

analysis 1820 - Brandes published the first synoptic weather maps. 1832 –Schilling invented electromagnetic telegraph


19th Century

1835 –Gaspard Gustave Coriolis demonstrated the effect of earth’s rotation on atmospheric motion (Coriolis effect)

1836 – Alter and Morse, independently invented the first known American electric telegraph

1846 – Robinson invented cup anemometer 1847 - Helmholtz published a definitive statement of the

conservation of energy, the first law of thermodynamics 1848 – Thomson (Kelvin) extended the concept of

absolute zero from gases to all substances. oK


19th Century

1852 - Joule and Thomson demonstrate that a rapidly expanding gas cools, later named the Joule-Thomson effect

1856 - Ferrel published essay on winds and currents of the oceans

1859 - Maxwell discovered the distribution law of molecular velocities.

1865-Manila Observatory founded in the Philippines. 1872 – Boltzman stated the Boltzman equation for the

temporal development of distribution funcitons in phase space.


20th century

1902 - Assman and de Bort independently discovered the stratosphere.

1904 – Bjerknes presented the vision that forecasting the weather is feasible based on mathematical methods.

1919 – Fujiwhara discussed the Fujiwhara effect, interaction of cyclones

1920 - Milankovic proposed that long term climatic cycles may be due to changes in the eccentricity of the Earth's orbit and changes in the Earth's obliquity.

1922 - Richardson organised the first numerical weather prediction experiment.


20th century

1923 - Walker described the oscillation effects of ENSO 1924 - Walker first coined the term Southern Oscillation. 1935 - IMO decided on the 30 years normal period (1900–

1930) to describe the climate. 1938 - Callendar first to propose global warming from CO2

emissions 1939 - Rossby identified the Rossby waves in the

atmosphere 1940 - high-flying military aircraft discovered the existence of

jet streams—swiftly flowing air currents that girdle the earth.


20th century

1953 - NOAA created a system for naming hurricanes using alphabetical lists of women's names

1959 - The first weather satellite, Vanguard 2 but unsuccessful

1960 - The first weather satellite to be considered a success was Tiros 1

1969 - Saffir-Simpson Hurricane Scale was created to describe hurricane strength on a category range of 1 to 5.

1971 - Fujita introduced the Fujita scale for rating tornadoes. 1975 - The first Geostationary Operational Satellite

(GOES) was launched in the orbit


20th century

1980s onwards, networks of weather radars are further expanded in the developed world.. Doppler weather radar is becoming gradually more common, adds velocity information.

1982 - The first Synoptic Flow experiment is flown around Hurricane Debby to help define the large scale atmospheric winds that steer the storm.

1988 - WSR-88D type weather radar implemented in the United States. Weather surveillance radar that uses several modes to detect severe weather conditions.

1992 - Computers first used in the United States to draw surface analyses. 1997 - Hare named the Pacific decadal oscillation 1998 - Improving technology and software finally allows for the digital

underlying of satellite imagery, radar imagery, model data, and surface observations improving the quality of United States Surface Analyses.


21st Century

2001 – National Weather Service begins to produce a Unified Surface Analysis, ending duplication of effort at the Tropical Prediction Center, Ocean Prediction Center and Hydrometeorological Center

2003 – NOAA hurricane experts issue first experimental Eastern Pacific Hurricane Outlook.

2004 – A record number of hurricanes strike Florida in one year 2005 – A record 27 named storms occur in the Atlantic. National Hurricane

Center runs out of names from its standard list and uses Greek alphabet for the first time.

2006 - Weather radar improved by adding common precipitation to it such as freezing rain, rain and snow mixed and snow for the first time.

2007 – The Fujita scale is replaced with the Enhanced Fujita scale for National Weather Service tornado assessments. The Enhanced Fujita Scale is slightly more accurate with the wind speeds and not much adjusted.

2010s - Weather radar dramatically advances with more detailed options.


Meteorology plays a major role in environmental science. It is helpful in determining and tracking climate patterns as well as how land and water play a role in the climate and climate change. It gives information on oscillations and how global oscillations may cause weather and climate disturbances.

The fields of applications are given below to illustrate the scope of meteorology.

Safe Navigation:

For safe navigation on sea the knowledge of adverse weather i.e. large tidal waves, ocean waves, high speed wind, cyclonic storms etc is needed which is supplied in weather forecast from meteorology.

Safe aviation:For transport through air, the pilots need the information about atmospheric conditions such as the electric lightening, high speed winds and their directions, thunder storms, foggy atmosphere etc. So pilots can go safely. For this purpose accurate forecasts are needed and are only possible from meteorology.

Importance of Meteorology

Industry:Many industries for their raw material depend on agricultural produce and accordingly location of industry is decided, so it is necessary to consider the weather and climate e.g. sugar mill, distillery, jute mill etc.

Animal Production:Beef, poultry and milk production also depend on weather and meteorology provides the information for successful animal production and animal husbandry.

Fisheries:Fishermen need information of atmospheric and oceanic changes before they proceed on sea for fishing and this is possible from meteorological knowledge. Production in Aquaculture and mariculture systems is also directly or indirectly affected by weather. Post harvest like fish drying is dependent on weather condition.

Irrigation and water resources:Meteorological and hydrological information assists in planning the location size and storage capacities of dams to ensure water supply for irrigation and domestic needs. When and how much to irrigate is also decided from the meteorological information.


Land use planning:The meteorological data supplemented with soil and topographic information help to plan the sites for the specific land use for drop production, forests, urban residence, industry etc.

Human Life:Human being tries to acclimatize himself with the prevailing weather conditions, for this they manage for type of clothing, housing food habit etc.◦ Clothing:

Warm cloths during winter and thin cloth during summer are used.◦ Housing:

Direction of windows, doors for proper ventilation, roofing-plain in low rainfall region whereas. Slanting roof in the areas where rainfall is more and frequent in occurrence.◦ Food habits:

Heavy diet during winter season is recommended whereas during summer season more quantum of water consumption is needed.


Human health:If any sudden change in the climatic conditions is

experienced it results into epidemics of material fever. Asthma patent suffers more during cloudy conditions.

Commerce: Trading of any item is made according to need of the

people in relation to weather prevailing e.g. Gum shoes, umbrella and raincoats are generally traded in rainy season only, woolen cloths in winter season and white cotton cloths. Cold drinks etc. are in more demand in summer season.


The relationship between oceanography and meteorology is of an order different from that between it and geology or biology, because meteorologic events do not take place within or under the water, as geologic and biologic do. But the state of the surface of the sea so directly affects that of the air above it that meteorologists are much concerned with certain phases of oceanography, while, on the other hand, the temperature, humidity, and movements of the air are as constantly tending to modify the physical state of the water below it.

The atmosphere affects the oceans and is in turn influenced by them. The action of winds blowing over the ocean surface creates waves and the great current systems of the oceans. When winds are strong enough to produce spray and whitecaps, tiny droplets of ocean water are thrown up into the atmosphere where some evaporate, leaving microscopic grains of salt buoyed by the turbulence of the air. These tiny particles may become nuclei for the condensation of water vapor to form fogs and clouds.

Meteorology and Oceanography

Meteorology and Oceanography

Atmospheric Environment Refers to the envelope of air

surrounding the Earth, including its interfaces and interactions with the Earth.

Chemical composition Optical Properties Mass Thickness Vertical structure

Atmospheric Environment

Atmospheric Environment

* 99% of dry air is composed of nitrogen (N2) and oxygen (O2).These gases provide a constant background but are not active ingredients for weather and climate.

Water Vapor (H2O)

Water vapor is an invisible gas – clouds are liquid water droplets and ice crystals

Critical component of atmosphere in regard to weather and climate a. Source of precipitation (rain, snow, etc.) b. Water is only element that can exist as solid (ice), liquid (water), or gas (water vapor) at temperatures found in earth’s environment “Latent heat”, an important source of energy that powers storms, is

released during condensation of water vapor to liquid water c. Critical “greenhouse gas”

Concentration in the atmosphere is highly variable in regard to both place and time

(Depends mostly on temperature, with near 0% in the arctic and up to 4% in the tropics).

Variable gases of the Atmosphere

Carbon Dioxide (CO2)

1. Trace gas contributing only 0.039% of the volume of the atmosphere

2. However, very important in regard to climate since it is an important “greenhouse” Gas

3. Carbon Dioxide Cycle◦ a. Removed from atmosphere as dissolves in oceans

Oceans contain 50x the amount of CO2 than the atmosphere◦ b. Removed by plants through photosynthesis◦ c. Enters atmosphere by evaporation from oceans, decay and

burning of plant matter, respiration and volcanic activity◦ d. This cycle creates an equilibrium that had maintained stable

levels of CO2 in the atmosphere (280 parts per million [ppm]) for thousands of years


Carbon Dioxide (CO2) e. Since the start of the industrial revolution (early

1800s) we have increased the amount of CO2 in the atmosphere by 40% due primarily to the burning of fossil fuels

f. Upsetting the Balance◦ 1. It takes millions of years for fossil fuels to form under

pressure as plant matter decays and is buried by overlying earth◦ 2. We have upset the balance created by the CO2 cycle by

putting carbon dioxide into the air in minutes, through burning of fossil fuels, what took millions of years to create

◦ 3. This has tremendous impact on climate change


Carbon dioxide cycle


Methane (CH4) and nitrous oxide (N2O)

These trace gases are present in even more miniscule concentrations but still have significant impacts on the behavior of the atmosphere

They are both significant greenhouse gases and, although naturally occurring, both are increasing in concentration due to human activities.


Ozone (O3) a. The vast majority (97%) is found in the stratosphere,

above the layer of the atmosphere where weather occurs.

b. Critical to maintaining life on earth◦ Ozone absorbs harmful, high-energy ultraviolet

rays from the sun so that they do not reach earth’s surface


Ozone hole is not technically a “hole” where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic that happens at the beginning of Southern Hemisphere spring (August–October).


Chlorofluorocarbons (CFCs) a. Manmade chemicals used for propellants, refrigerants and

solvents b. Function as greenhouse gas but have a more important impact

in reducing ozone levels in the stratosphere c. Release chlorine atoms which facilitate chemical reactions that

destroy ozone, particularly in cold stratospheric clouds that form in winter

d. Result is an “ozone hole”, a reduction in ozone concentration over the polar regions, particularly in the southern hemisphere, which peaks in early spring

e. During spring and summer, the concentrations of ozone “mix out” with lower latitudes which has caused a decrease in ozone concentrations in middle latitudes (U.S.) as well

f. Production of CFCs has been eliminated but unfortunately they breakdown very slowly


In the stratosphere, the CFCs break down and release chlorine.

The chlorine reacts with ozone molecules, which normally block incoming ultraviolet radiation.

CFCs have a lifetime in the atmosphere of about 20 to 100 years, and consequently one free chlorine atom from a CFC molecule can do a lot of damage, destroying ozone molecules for a long time

CFCs effect on ozone layer

1. Clouds Remember, clouds are liquid water droplets, not

water vapor. 2. Aerosols a. The atmosphere is also filled with numerous tiny solid

or liquid suspended particles of various composition, called aerosols

b. Examples include dust and soil picked up by the wind, salt from sea spray, smoke from fires and ash from volcanic eruptions

c. These aerosols serve an important function as they act as surfaces which facilitate the condensation of water droplets to form clouds

Liquids and Solids forms in the Atmosphere

The Earth’s atmosphere is relatively transparent to incoming solar radiation and opaque to outgoing radiation emitted by the Earth’s surface.

The blocking of outgoing radiation by the atmosphere, popularly referred to as the greenhouse effect, keeps the surface of the Earth warmer than it would be in the absence of an atmosphere.

Important aspects are radiation, absorption, refraction and scattering

Optical Properties of the Atmosphere

The thickness of the Earth's atmosphere is not a definite number, but is estimated to be about 1000 km. Some says it’s between 100 km to 10,000 km. The reason that there is no definite number is because there is no set boundary where the atmosphere ends.

Thickness of the Atmosphere

The thickness of the atmosphere is geographically dependent where polar areas have thinner atmosphere while the in the tropics and equator have thicker atmosphere.

At any point on the Earth’s surface, the atmosphere exerts a downward force on the underlying surface due to the Earth’s gravitational attraction. The downward force, (i.e., the weight) of a unit volume of air with density is given by:

Force = density x gravity Ps = mass x gravity (Ps- atmospheric pressure) Gravity = 9.807 m s-2

Average mean atmospheric pressure= 985 hPa Pressure= 1013.25 mb = 1013.25 hPa _=29.92 in. Hg.

Mass of the Atmosphere

Mass = Ps/ gravity = 985 x 102 Pa/hPa/9.807 m s-2

= 1.004 x 104 kg m-2

The mass of the atmosphere Matm = 4RE 2 x m = 4 x (6.37 x 106)2 m2 x 1.004 x 104 kg m-2

= 5.10 x 1014 m2 x 1.004 x 104 kg m-2

= 5.10 x 1018 kg The total mean mass of the atmosphere is 5.1480 × 1018 kg or Mass = 5.17 * 1019 Newtons / 9.8 ms-2 = 5.27 * 1018 kilograms

Mass of the Atmosphere

A. Pressure and Density

1. Air density- number of air molecules within a given space Density = mass/volume Due to compressibility, near surface air is more dense than that above This may be expressed in terms of the mean free path, or average distance a

molecule travels before colliding with another molecule. Weight = mass x gravity Force = density x gravity 2. Air pressure- the amount of force exerted by the air molecules on earth’s surface due to gravity or the weight of a column of air above any given

point

Pressure= force/area

Vertical structure of the Atmosphere

Air molecules are attracted to the earth by gravity, which decreases with distance from the earth, therefore, air density and pressure always decrease with height above earth’s surface


Atmospheric Pressure At sea level, average atmospheric pressure = 1013.25 mb (round off

to 1000 mb) = 29.92 in Hg (14.7 pounds per square inch (lbs./in2) Due to greater gravity near earth’s surface and compression of the

molecules from above, atmospheric pressure decreases rapidly with height near earth’s surface and then more slowly at higher altitudes

At only 18,000 ft. above the surface atmospheric pressure is only ½ of the pressure at the surface, or 500 mb

At the height of Mt. Everest (29,000 ft.) the pressure is 300 mb which means 70% of the air molecules are below you

This low air pressure and density is why it is difficult to get enough oxygen to breath at this altitude

The atmosphere extends hundreds of miles up, becoming thinner and thinner, eventually merging with outer space



Atmospheric Layers of the Atmosphere based on temperature profile

◦ Troposphere (0-20 km)◦ Stratosphere (16-50 km)◦ Mesosphere (50-90 km)◦ Thermosphere (90- 400 km)◦ Exosphere (> 400 km)

Atmospheric Layers

Troposphere (0-20 km) (from Greek word, tropein - to change, circulate or mix) is the lowermost layer of the Earth's atmosphere.

Troposphere

Air temperature normally decreases with height.The rate at which the air temperature decreases with height is called the temperature lapse rate.The average (or standard) lapse rate in this region of the loweratmosphere is about 6.5°C for every 1000 m rise in elevationAverage thickness of 7 km, highest in the equator (17 km), thinnest at the poles (7 km)

Highest amount of water vapor (99%) and carbon dioxide

Clouds presence Where weather and climate

exist The term troposphere was

first used in 1902 by Leon Philippe Teisserenc de Bort, a French meteorologist who was a pioneer in the use of meteorological balloons.

Troposphere

The boundary between the troposphere and the stratosphere, where an abrupt change in lapse rate usually occurs.

Tropopause

It is defined as the lowest level at which the lapse rate decreases to 2 °C/km or less, provided that the average lapse rate between this level and all higher levels within 2 km does not exceed 2 °C/km.The tropopause is not a well-defined “layer” but a transition zone and varies in height from location to locationCommercial airlines prefer to fly just above the tropopause, in the lower stratosphere, to avoid turbulent vertical motions

Tropopause

Stratosphere (16-50 km)- is the second layer of the atmosphere.

Stratosphere

characterized by isothermal structure in the lower portion followed by increasing temperature in the upper portion. This temperature profile is due to the presence of ozone which absorbs ultraviolet rays from the sun, heating the surrounding airStability generally limits vertical extensions of cloudLess dense than troposphereLess water vapor25 km ozone layerRare cloudsJet streams

http://www.uvs-model.com/pictures/atmospheric_layers.jpg

The ozone layer is a region of concentration of the ozone molecule (O3) in the Earth's atmosphere. The layer sits at an altitude ofabout 10-50 kilometers, with a maximum concentration in the stratosphere at an altitude of approximately 25 kilometers.

Ozone layer

Blocks harmful ultraviolet rays from the sun (UV-C)Less energetic, but still dangerous (causes sunburn and skin cancer), UV-B penetrates the atmosphere to earth’s surface in small amounts but is absorbed and neutralized by the pigment in our skin (melanin)UV-B is necessary for production of vitamin D

Stratopause- is the boundary between two layers: the stratosphere and mesopshere.

50 to 55 kilometres high above the Earth's surface.

Atmospheric pressure – 1 millibar

Temperature -15oC

Stratopause


Mesophere (50-90km)- coldest layer of the atmosphere (-143oC).

Mesosphere

Strong temperature decreaseair is extremely thin and pressure very lowPresence of ionized or electrified air- D layer- caused by the action of UVR on air moleculesWhere meteors are burn before entering the earthVarious phenomena: Cosmic rays, Noctilucent or night shining clouds (water vapor) and Air glow( light due to reradiation of sunlight to heated atmosphere particles).


Mesopause (85 km) is the boundary between the mesophere and thermosphere.

Mesopause

The first 10 km of the mesopause are almost isothermal. Presence of noctilucent clouds composed of ice crystals on meteoric dustIncreased CO2 in the mesopshere acts to cool the atmosphere due to increased radiative emission by CO2.


Thermosphere (90-400 km)- hottest layer where air temperatures can exceed 1000° C (1800° F), primarily due to oxygen absorbing the sun’s energetic rays.

Thermosphere

Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher.O3, CO2 and H2O are virtually absentLow densityBroken atoms/ no moleculesAbundant free particles of negative electricity or electronsImportant to communications


Electrically charged layer located between 80 to 400 km above sea level where molecules of nitrogen and atoms of oxygen are readily ionized as they absorb.

Important to radio communications The auroras occur in this layer Auroras- northern and southern lights Aurora borealis- northern lights Aurora australis- southern lights

The aurora forms when charged particles emitted from the sun during a solar flare penetrate the earth's magnetic shield and collide with atoms and molecules in our atmosphere. These collisions result in countless little bursts of light, called photons, which make up the aurora.

Thermosphere

Thermopause (>400 km) is the boundary between the thermosphere and exosphere.

Thermopause

Space missions such as the ISS, space shuttle, and Soyuz operate under this layer.Portion of magnetosphere is found in this layerMagnetosphere or protosphere- the upper layer of the thermosphere. The earth’s magnetic field is more important here than the gravitational field in controlling the behavior of protons.

Exosphere (> 400 km) is the outermost layer of the atmosphere.

Exosphere

Gases are extremely thinH2 dominantUVR dominantVariable temperature (0oC to 1700oC)O2 and other elements exist in atomic formsGeocorona is the name for the exosphere's part that is seen from earth (luminous part of the exosphere)transitional zone between Earth's atmosphere and space

Gravitational force from a point is higher closer to it and reduces with increasing distance from it. Because the Earth itself is broader at equator, the equator experiences less gravity allowing air to reach bigger heights. Poles are closer to gravitational center and experience higher gravity.

Earth is rotating at a rate of 24 hours per spin. Not just the ground, but also the atmosphere is spinning with it. The gas molecules at poles are closer to this rotational axis while those near the equator are farther away on a larger radius. Therefore, air at equator experience a greater centrifugal force and moves farther away from Earth.

Earth's orientation in space allows equator to be closer to the Sun. Due to this higher gravity, atmosphere deforms slightly towards the sun while draining a bit more air from the poles.

Regions near equator receives more sunlight than the poles making them hotter and less air dense. So equatorial gases reaches greater heights to exert the same pressure as at the poles.

Just like the tides, Moon's gravity causes the atmosphere to deform. Since the moon orbits close to the equator, equatorial thickness is increased.

Why Atmosphere is thicker in the equator?

Atmospheric Layers based on gas composition

◦ Homosphere – the region of fairly uniform amount of gases (78 percent nitrogen, 21 percent oxygen) by turbulent mixing located below the thermosphere.

◦ Heterosphere- the region of variable amount of gases. This is due to the infrequent collisions between atoms and molecules and the air is unabale to keep itself stirred. As a result, diffusion takes over as heavier atoms and molecules (such as oxygen and nitrogen) tend to settle to the bottom of the layer, while lighter gases (such as hydrogen and helium) float to the top.

Atmosphere Layers

Homosphere and Heterosphere

The ionosphere is not really a layer, but rather an electrified region within the upper atmosphere where fairly large concentrations of ions and free electrons exist.

Ionosphere

The ionosphere is defined as the layer of the Earth's atmosphere that is ionized by solar and cosmic radiation. It lies 75-1000 km (46-621 miles) above the Earth.The ionosphere has major importance to us because, among other functions, it influences radio propagation to distant places on the Earth, and between satellites and Earth.

D-layer- lowest layer containing the least amount of ions.

E-layer- (Kennelley-Heaveside layer), the middle layer containing a higher concentration of ions

F-layer- (Appleton layer)- containing the highest concentration of ions

Distinct Layers of the Ionosphere

Distinct Layers of the Ionosphere

Night time During the night (image below, right side), the ionosphere has only

the F and E layers. A VLF wave from a transmitter reflects off the ions in the E layer and bounces back.

Daytime During the daytime, the Sun’s X-ray and UV light increase the

ionization of the ionosphere, creating the D and enhancing the E layers, and splitting the F region into 2 layers. The D layer is normally not dense enough to reflect the radio waves. However, the E layer is, so the VLF signals go through the D layer, bounce off the E layer, and go back down through the D layer to the ground. The signals lose energy as they penetrate through the D layer and hence radios pick up weaker signals from the transmitter during the day. When a solar flare occurs, even the D layer becomes ionized, hence allowing signals to bounce off it.

Ionosphere

Earth is unique. Not only does it lie at just the right distance from the sun so that life may flourish, it also provides its inhabitants with an atmosphere rich in nitrogen and oxygen — two gases that are not abundant in the atmospheres of either Venus or Mars, our closest planetary neighbors.

Planetary atmosphere

Planetary Atmosphere

Atmosphere evolved in 4 steps: ◦primordial gases (He, H2), later lost from sun's

radiation ◦exhalations from the molten surface (volcanic

venting); bombardment from icy comets ◦steady additions of carbon dioxide, water vapor,

carbon monoxide, nitrogen, hydrogen, hydrogen chloride, ammonia, and methane from volcanic activity

◦addition of oxygen by plant/bacterial life

Origin of the Atmosphere

It is believed that there was intense volcanic activity for the first billion years of the Earth's existence – the early atmosphere was probably mostly carbon dioxide, with little or no oxygen

There were smaller proportions of water vapour, ammonia and methane

As the Earth cooled down, most of the water vapour condensed and formed the oceans

It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth


Earth’s atmosphere has changed drastically over the last 4 billions years…


Carbon dioxide

Methane Ammonia Nitrogen Oxygen Others

4 billion years ago Present day2 billion years ago

The proportion of oxygen went up because of photosynthesis by plants

The proportion of carbon dioxide went down because: -◦ It was locked up in sedimentary rocks, such as limestone,

and in fossil fuels◦ It was absorbed by plants for photosynthesis◦ It is dissolved in the oceans

The burning of fossil fuels is adding carbon dioxide to the atmosphere faster than it can be removed meaning the level of carbon dioxide in the atmosphere is increasing

Atmospheric changes

As oxygen levels rose atmospheric ammonia (NH3) reacted with oxygen (O2) to form water (H2O) and nitrogen (N2)

Also, living organisms, including denitrifying bacteria, broke down nitrogen compounds releasing more nitrogen into the atmosphere

Nitrogen is volatile in most of its forms An inert gas, not reactive with other materials It is very stable in the presence of solar radiation And so the atmosphere headed towards a

composition that has remained fairly constant for the last 200 million years

Atmospheric changes