STRUCTURE OF THE ATMOSPHERE

STRUCTURE OF THE ATMOSPHERE

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  Lesson 1Lesson 1 Structureof theStructure of the AtmosphereAtmosphere Specification: Major climate controls
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  DefinitionsDefinitions  Weather –day to day changes inWeather – day to day changes in the state of the atmosphere.the state of the atmosphere.  Climate – average weatherClimate – average weather conditions over a longer period ofconditions over a longer period of time – 30 years.time – 30 years.
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  What is theAtmosphere?What is the Atmosphere? An atmosphere is defined as the gaseousAn atmosphere is defined as the gaseous envelope that surrounds a celestial body.envelope that surrounds a celestial body. Therefore, the Earth, like other planets inTherefore, the Earth, like other planets in the solar system, has an atmosphere, whichthe solar system, has an atmosphere, which is retained by gravitational attraction andis retained by gravitational attraction and largely rotates with it.largely rotates with it.
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  Who studies theAtmosphere?Who studies the Atmosphere? Learning about different states of theLearning about different states of the atmosphere enables science to understandatmosphere enables science to understand and predict changes on a range of scales.and predict changes on a range of scales. Meteorology is the subject that studiesMeteorology is the subject that studies the chemical and physical properties ofthe chemical and physical properties of the atmosphere together with its fields ofthe atmosphere together with its fields of motion, mass and moisturemotion, mass and moisture..
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  How was isformed?How was is formed? At the time of the Earth's formation around 4.5 billion years ago there wasAt the time of the Earth's formation around 4.5 billion years ago there was probably no atmosphere. It is believed to have come into existence as aprobably no atmosphere. It is believed to have come into existence as a result of the volcanic expulsion of substances from its interior, mainlyresult of the volcanic expulsion of substances from its interior, mainly water vapour, with some carbon dioxide, nitrogen and sulphur. Thewater vapour, with some carbon dioxide, nitrogen and sulphur. The atmosphere can only hold a certain amount of water vapour, so the excessatmosphere can only hold a certain amount of water vapour, so the excess condensed into liquid water to form the oceans.condensed into liquid water to form the oceans. It is thought that the first stage in the evolution of life on Earth requiredIt is thought that the first stage in the evolution of life on Earth required an oxygen-free environment. Later primitive forms of plant life developedan oxygen-free environment. Later primitive forms of plant life developed in the oceans and began to release small amounts of oxygen into thein the oceans and began to release small amounts of oxygen into the atmosphere as a waste product from the cycle of photosynthesis: H2O +atmosphere as a waste product from the cycle of photosynthesis: H2O + CO2 + sunlight sugar + O→CO2 + sunlight sugar + O→ 22 This build-up of atmospheric oxygen eventually led to the formation of theThis build-up of atmospheric oxygen eventually led to the formation of the ozone layer. This layer, approximately 8 to 30 km above the surface, helpsozone layer. This layer, approximately 8 to 30 km above the surface, helps to filter the ultraviolet portion of the incoming solar radiation. Therefore,to filter the ultraviolet portion of the incoming solar radiation. Therefore, as levels of harmful ultraviolet radiation decreased, so plants were able toas levels of harmful ultraviolet radiation decreased, so plants were able to move to progressively higher levels in the oceans.move to progressively higher levels in the oceans. This helped to boost photosynthesis and thereby the production of oxygen.This helped to boost photosynthesis and thereby the production of oxygen. Today, this element has reached levels where life has been sustainable onToday, this element has reached levels where life has been sustainable on the surface of the planet through its presence, and it should bethe surface of the planet through its presence, and it should be remembered that oxygen is an element which is not commonly found inremembered that oxygen is an element which is not commonly found in the universe.the universe.
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  Composition of theCompositionof the atmosphereatmosphere Main Elements = 99%Main Elements = 99% Nitrogen (NNitrogen (N22)) 78%78% Oxygen (0Oxygen (022)) 21%21% Trace Elements = 1%Trace Elements = 1% Xenon (Xe)Xenon (Xe) Argon (Ar)Argon (Ar) Ozone (OOzone (O33)) Carbon Dioxide (COCarbon Dioxide (CO22)) Nitrogen Dioxide (NONitrogen Dioxide (NO22)) Neon (Ne)Neon (Ne) Iodine (I)Iodine (I) Helium (He)Helium (He) Carbon Monoxide (CO)Carbon Monoxide (CO) Methane (CHMethane (CH44)) Ammonia (NHAmmonia (NH33)) Nitrous Oxide (NNitrous Oxide (N22O)O) Water Vapour (HWater Vapour (H220)0)
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  Vertical structure ofthe atmosphereVertical structure of the atmosphere The atmosphere is dividedThe atmosphere is divided intointo fourfour isothermal layers orisothermal layers or 'spheres':'spheres': troposphere,troposphere, stratosphere, mesospherestratosphere, mesosphere and thermosphere.and thermosphere. Each layer is characterised byEach layer is characterised by a uniform change ina uniform change in temperature with increasingtemperature with increasing altitude.altitude. In some layers there is anIn some layers there is an increase in temperature withincrease in temperature with altitude, whilst in others italtitude, whilst in others it decreases with increasingdecreases with increasing altitude.altitude. The top or boundary of eachThe top or boundary of each layer is denoted by a 'pause'layer is denoted by a 'pause' where the temperature profilewhere the temperature profile abruptly changesabruptly changes ..
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  TroposphereTroposphere The troposphere containsaboutThe troposphere contains about 80%80% of the atmosphere and isof the atmosphere and is the part of the atmosphere in which we live, and makethe part of the atmosphere in which we live, and make weather observations.weather observations. In this layer, average temperatures decrease with heightIn this layer, average temperatures decrease with height 6.46.4oo c/1000m, as there is less air in contact with the ground toc/1000m, as there is less air in contact with the ground to heat up. This is known asheat up. This is known as Environmental Lapse rateEnvironmental Lapse rate (adiabatic(adiabatic cooling brought about by changes in temperature caused by acooling brought about by changes in temperature caused by a decrease in pressure at height).decrease in pressure at height). This sphere mixes vertically by convection, conduction andThis sphere mixes vertically by convection, conduction and turbulence more than any other sphere. These vertical motionsturbulence more than any other sphere. These vertical motions and the abundance of water vapour make it the home of alland the abundance of water vapour make it the home of all important weather phenomena.important weather phenomena. The troposphere is aroundThe troposphere is around 16 km high16 km high at the equator, with theat the equator, with the temperature at the tropopause around –80 °C. At the poles,temperature at the tropopause around –80 °C. At the poles, the troposphere reaches a height of around 8 km, with thethe troposphere reaches a height of around 8 km, with the temperature of the tropopause around –40 °C in summer and –temperature of the tropopause around –40 °C in summer and – 60 °C in winter. Therefore, despite the higher surface60 °C in winter. Therefore, despite the higher surface temperatures, the tropical tropopause is much cooler than attemperatures, the tropical tropopause is much cooler than at the poles at the thickness is increased – more cooling occurs.the poles at the thickness is increased – more cooling occurs.
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  StratosphereStratosphere Temperatures in thestratosphere rise with increasingTemperatures in the stratosphere rise with increasing altitude (creating a temperature inversion) this isaltitude (creating a temperature inversion) this is caused by concentrations on Ocaused by concentrations on O33 which absorbswhich absorbs ultraviolet radiation. This is greatest around 50 km atultraviolet radiation. This is greatest around 50 km at the edge of the stratopause. Temperatures range from –the edge of the stratopause. Temperatures range from – 30 °C over the winter pole to +20 °C over the summer30 °C over the winter pole to +20 °C over the summer pole according to latitude and season.pole according to latitude and season. As well as a noticeable change in temperature, theAs well as a noticeable change in temperature, the move from the troposphere into the stratosphere is alsomove from the troposphere into the stratosphere is also marked by an abrupt change in the concentrations ofmarked by an abrupt change in the concentrations of the variable trace elements. Water vapour decreasesthe variable trace elements. Water vapour decreases sharply, whilst ozone concentrations increase. Thesesharply, whilst ozone concentrations increase. These strong contrasts in concentrations are a reflection ofstrong contrasts in concentrations are a reflection of little mixing between the moist, ozone-poorlittle mixing between the moist, ozone-poor troposphere and the dry, ozone-rich stratosphere.troposphere and the dry, ozone-rich stratosphere. The stratosphere extends up to around 48 km above theThe stratosphere extends up to around 48 km above the surface, and together with the troposphere, theysurface, and together with the troposphere, they account for 99.9% of the Earth's atmosphere.account for 99.9% of the Earth's atmosphere.
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  MesosphereMesosphere Temperatures in themesosphere decreaseTemperatures in the mesosphere decrease rapidly as there is no water vapour, cloud, dustrapidly as there is no water vapour, cloud, dust or ozone to absorb incoming radiation.or ozone to absorb incoming radiation. Temperatures at the mesopause go as low as –Temperatures at the mesopause go as low as – 120 °C with very strong winds – 3000km/hr.120 °C with very strong winds – 3000km/hr. As in the troposphere, the unstable profile meansAs in the troposphere, the unstable profile means that vertical motions are not inhibited. Duringthat vertical motions are not inhibited. During the summer, there is enough lifting to producethe summer, there is enough lifting to produce clouds in the upper mesosphere at high latitudesclouds in the upper mesosphere at high latitudes
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  ThermosphereThermosphere The thermosphere extendsupwards to altitudes ofThe thermosphere extends upwards to altitudes of several hundred kilometres, where temperaturesseveral hundred kilometres, where temperatures range from 250range from 250oo c to as high as 1,700c to as high as 1,700oo c, getting warmerc, getting warmer with increasing height.with increasing height. Temperature ranges depend on the degree of solarTemperature ranges depend on the degree of solar activity and as there is more atomic oxygen there (likeactivity and as there is more atomic oxygen there (like ozone) to absorb the heat.ozone) to absorb the heat. The temperature changes between day and nightThe temperature changes between day and night ((DiurnalDiurnal) amount to hundreds of degrees.) amount to hundreds of degrees. Above 500 km temperatures are very difficult toAbove 500 km temperatures are very difficult to define. Molecules are so widely spaced that they movedefine. Molecules are so widely spaced that they move independently, and there is no reason why theirindependently, and there is no reason why their temperatures should be the same.temperatures should be the same.
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  EarthEarth’’s Annual HeatBudgets Annual Heat Budget – Heating of the Atmosphere– Heating of the Atmosphere At ‘A’ the sun’s energy is more concentrated on a small land area – intense heating. At ‘B’ the sun’s energy is spread over a wider surface area – leading to less direct heating. ‘A’‘B’ ‘B’
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  Heat Budget inOUR WinterHeat Budget in OUR Winter In the North in OUR Winter there is a deficit In the South in OUR Winter there is a surplus At the equator there is a surplus Of course the Earth’s heat budget is not that simple! You have to remember the effects of seasonality – the seasonal shift in the trace of the sun on the Earth’s surface during it’s orbit.
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  Heat Budget inOUR SummerHeat Budget in OUR Summer In the South in OUR Summer there is a deficit In the North in OUR Summer there is a surplus At the equator there is a surplus
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  EarthEarth’’s Annual HeatBudgets Annual Heat Budget So over the pattern of a year the Earth’s heat budget changes with the seasons, however there is always a surplus at the equator. The uneven distribution of heating across the Earth is what drives the air to move (WIND) in an effort to redistribute the heat to areas of deficit.