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Atmosphere Part I Energy
Contents w w w w w Introduction Composition of Air Structure of the Atmosphere Energy System Energy Input Energy Transfer within the earth Energy Budget / Heat Budget Horizontal Heat Transport World distribution of temperature Human Impact on Atmospheric Energy
Introduction w Atmosphere consists of a mixture of various gases surrounding the earth to a height of many km. w Meteorology deals with the physics of this atmosphere
Composition of Air w Permanent Gases – They always keep in a fixed proportion in the atmosphere. w Changing Gases – They are changing in difference places and time. w Solid Impurities
Changing Gases w Generally speaking, they are carbon dioxide (CO 2), Vapour (H 2 O) and Ozone (O 3). w CO 2: – Distributed in the lowest layer of the Atmosphere (Troposphere) – 0. 03% – It is one of the major green-house gases which can absorb terrestrial radiation (long wave radiation). – Major source of CO 2 is the combustion of fossil fuel such as Coal, Oil, Gas, ….
Changing Gases - 2 w H 2 O : – The proportion of H 2 O in the atmosphere is about 04% (Various in difference places). – The source of H 2 O is evapo-transpiration from plants and water bodies. – 50 -60% H 2 O is distributed over the land 1. 5 km-2. 5 km. – It is fundamental to many essential meteorogical processes and all weather phenomena. w O 3 – It is distributed in the Ozone layer (over land 2025 km) in the Stratosphere. – It absorb most short wave radiation from the universe and protects the living bodies of the earth. w Others: – They are present in extremely minute percentages.
Changing Gases -3 w Solid Impurities – Include dust (man-created pollution), chemical salt, pollen, smoke…. . etc. – They make the air look like dirty and reduce the visibility. – They can absorb much long wave radiation and cause temperature increase. – They are also condensation nuclei forming water droplets.
Structure of the Atmosphere
Troposphere w Its thickness approximately 8 km (polar region) to 16 -19 km (equatorial region). w Almost all weather phenomena, 75% of total mass of air, virtually all water vapour and aerosols are in this zone. w Vertical turbulence are most marked. w With Environmental Lapse Rate (-6. 5 o. C/km) w Ceiling of the troposphere is called tropopause.
Stratosphere w From the tropopause to about 50 km. w The lower layer is isothermal layer. w Cirrus clouds occasionally form in the lower stratosphere. w Isothermal layer terminates at a height of about 20 km and replaced by a inversion layer (temperature increase with height) w At the stratopause, a reversal to falling temperature sets in.
Mesosphere and Thermosphere w Mesosphere – From the stratopause to 80 km. – Temperature falling with height. – Ceiling is called mesopause. w Thermosphere – From the mesopause to space (no well-defined upper limit). – Temperature increase with height.
Energy System w Atmos. is open energy system. w It receives energy from both directions (earth and sun). w Compared with sun (solar energy), earth’s energy can be negligible. w All life processes and all exchanges of matter and energy between the earth’s atmos. and the surfaces of the oceans and lands are driven by solar energy. w The planetary circulation systems of atmos. and oceans are also driven by solar energy. w Water changes in various forms (liquid, solid and gas) over the globe also driven by solar energy. w Sun is the energy source of the earth.
Energy Input – Solar Radiation w Importance – It is a electro-magnetic wave energy radiating from sun, which is also called insolation. – All weather phenomena are affected by various meteorology parameters which all affected by insolation. – Solar radiation is essential for photosynthesis. – The water cycle is driven by solar insolation.
Solar Radiation w Nature: – Emitted from sun (surface temperature 6000 o. C) – It is a spectrum (combination energy of different wavelengths) – Most of it is visible light rays (short-wave) – Energy emitted by earth (surface temp. 15 o. C) is terrestrial radiation (long-wave) – Higher temperature of an object emits shorterwave of radiation.
Spectrum of solar rays
Spectrum of solar rays - 2 w Short-wave radiation (wavelength < 0. 8 micron) – Ultra-violet, x-rays, gamma rays, • Invisible and harmful for living organisms. • Most of them absorbed by thermosphere and ozone layer. – Visible lights (violet, indigo, blue, green, yellow, orange and red). • 90% of solar rays. • It provides most of the heat energy to the atmosphere. w Long-wave radiation (wavelength > 0. 8 micron) – Infrared, micro waves and radio waves – They are also absorbed by ozone, CO 2 and clouds.
Spectrum of solar rays - 3
Energy Transfer within the earth w Receipt of solar radiation at the top of the atmosphere. w Receipt of solar radiation at the earth’s surface.
At the top of the atmosphere w Four factors – – Solar output Distance between the sun and the earth Angle of solar incidence Length of daytime.
Four factors w Solar output – There are 11 years cyclic variations of 1% in the output of solar energy. – More energy can be received when sunspot activity is less active. w Distance from the sun – Perihelion: closest to the sun (147. 3 million km) on 3 rd January. – Aphelion: farthest to the sun (152. 1 million km) on 4 th July. – 7% of the total energy difference. – Solar constant: 1. 9 cal/cm 2/min. or 2 cal/cm 2/min.
Four factors w Angle of incidence – It is the angle between the sun’s rays and the horizon. – Greater the angle of incidence, the more concentrated energy, hence higher is the temperature. – Intensity of insolation is greatest where the sun’s rays strike vertically. – Polar regions receive the least heat per unit area. – Temperatures are maximal at low latitudes and minimal near the poles. – Angle of incidence is affected by latitude, the time of day, seasons and length of daytime.
Angle of incidence - Latitude Solar incidence various between different latitudes of the earth surface.
Angle of incidence – Time of day w The angle of incidence increases from sunrise to a maximum during noon-time. w It decreases in the afternoon to another minimum during sunset.
Angle of incidence - Seasons w Because of the occurrence of rotation, revolution and the tilted of earth axis (66. 5 o to the horizontal), the mean angle of solar incidence a any place is constantly changing.
Angle of incidence – Length of daytime w The longer the daytime (time between sunrise and sunset) , the more solar radiation is received.
At the earth’s surface w Solar energy received at the earth surface is much less than that received at the top the atmosphere. w It is due to the effects of the atmos. , cloud cover, different surface covers, latitudes, elevation and aspect.
At the earth’s surface - 1 w Effect of the atmosphere: – Some solar radiation will be lost in passing through the atmos. with absorption, reflection and scattering by various gases, water vapour, dusts and clouds – Basic terms • Transmit: solar energy passes through an object and the object cannot gain any energy. • Absorb: some energy has been captured by the object. • Reflect: radiation change the moving direction in a regular paths. . • Diffuse reflection / Scattering: radiation change the moving direction in irregular paths.
At the earth’s surface - 2 w Effects of cloud cover: – Cloud cover is a significant barrier to the penetration of insolation. – The amount of reflection depends on the amount of cloud cover, its thickness and cloud type. – The upper surface of clouds are extremely good reflectors of short-wave radiation. – Average for cloud reflection and absorption are 21% and 3% respectively. – Cloud cover also serves to retain much of heat that would be lost from the earth by radiation.
At the earth’s surface - 3 w Effects of surface covers: – Snow and ice have high albedos and much of the incoming radiation will be reflected back to space. – Water has a tendency to store heat it receives, but land quickly returns it to the atmos. • Land surface heats and cools much quicker than ocean. • Annual and diurnal range of temperatures are greater in continental than in coastal locations. • Heat storage in oceans causes them to be warmer in winter and cooler in summer than lands in the same latitude.
At the earth’s surface - 3 w Table of albedos
At the earth’s surface - 4 w Effect of Latitude – Latitude determines the annual distribution of insolation. – High latitudes areas receive less radiation. • The same amount of insolation is spread over in a larger surface. • The same solar beam undergoes more severe atmos. dilution by reflection, scattering and absorption in passing through a thicker layer of atmos. • There is a general latitudinal decrease from the equator to the poles.
At the earth’s surface - 5 w Effect of elevation and aspect – In middle latitudes, the intensity of incident solar radiation increases by 5 -15% for each 1000 m increase in elevation in the lower troposphere.
Energy Budget / Heat Budget
Energy Budget / Heat Budget -1 w Insolation (Short-wave radiation) – Let there are 100 units energy come from the sun – The total reflection of the earth is about 32 units (albedo) • The amount of reflection from clouds and water droplets depend on weather and climatic conditions. • The amount of clouds in desert is small. But thick clouds in humid conditions may reflect up to 80% of the total incoming solar radiation. – About 18 units absorbed by atmosphere (Ozone, water vapour, CO 2. • About 8 units directly – Aad, about 10 units indirectly (Aai). – Only about 50 units can be reached the earth’s surface. • About 26 units absorbed by surface directly (ASd) • About 18 units absorbed by surface indirectly (ASi) • About 6 units scattering from the atmosphere (Si)
Energy Budget / Heat Budget - 2 w Terrestrial Radiation (Long-wave radiation) – The surface receives about 77 units from atmos. Through counter-radiation (CR). – About 8 units are lost directly back to space through Atmospheric Windows (Aw). – About 90 units are radiated to the atmosphere (RL). – About 29 units are emitted to the atmosphere by Latent Heat (E). – About 9 units are emitted to the atmosphere by Sensible Heat (H). – About 60 units are lost into space from the atmosphere (RO). Most of them are radiated from the top of clouds.
Energy Budget / Heat Budget - 3
Energy Budget / Heat Budget - 4 w Green House Effect: – The atmosphere is largely heated from earth’s surface and it is warmed by trapping long wave terrestrial energy producing the green house effect. – Long-wave radiation from ground, a portion is radiating back to the earth’s surface, the process is called counterradiation. – Short-wave radiation permitted to pass through atmosphere, but the long-wave form is delayed in making its escape. – Water vapour, clouds and carbon dioxide acts as a blanket which returns heat to the earth and help to keep surface temperatures from dropping excessively during night and in winter.
Horizontal Heat Transport w Variation in Receipt of Heat Energy – The receipt of heat energy is very unequal geographically. – Near the equator, about 50% of the insolation reaches the ground, but near the poles less than 20%. • Sun’s rays pass through a thicker atmosphere and cause greater energy losses by reflection and absorption. • Surface albedo (snow-covered surface) is much greater in high latitudes.
Horizontal Heat Transport - 1 w 40 o. N to 30 o. S is the region of surplus. w Two high-latitude regions of deficit. w Energy balance can be maintained only if heat is transported from lowlatitude surplus belt to high-latitude deficit regions. w The rate of meridional heat transport is greatest in middle latitudes.
Horizontal Heat Transport - 2 w The effect of atmospheric circulation – In the form of both latent heat and sensible heat. – Zone of max total transfer rate is found between latitudes 35 o and 45 o in both hemispheres. – Latent heat transport almost occurs in the lowest 2 or 3 km. – Sensible heat has a double maximum not only latitudinally but also in the vertical plane.
Horizontal Heat Transport - 2
Horizontal Heat Transport - 3 w Effect of Ocean Currents – Characteristics of ocean water • Larger specific heat • Transparency: insolation can penetrate to a great depth • Circulation: surface warm water can down to deep sea, and the cold water can also transport to surface. • Not all solar energy use for water heating, but for evaporation (about 1/3 energy).
Horizontal Heat Transport - 3
Horizontal Heat Transport - 3 w Warm Currents refer to the sea water from low latitude areas to high latitude areas. – Eg. Gulf Stream, Kuro Siwo Currents. w Effects of Gulf Stream on Europe Climate. – The distance between the west and east coasts of the N. Atlantic Ocean is comparative short, which enables it to preserve heat energy in sea water. – Predominantly west-east structure of European mountain ranges. – The prevailing westerly winds penetrate the warm moist air, that is carried by Gulf Stream, into the Europe. w In the Southern hemisphere, the temperature of sea water is lower than N. hemisphere for large quantities of cold water from melting ice around Antarctica.
Horizontal Heat Transport - 3 w Cold Currents refer to those moving from high latitude areas to low latitude areas. w Two categories – The low latitude cold currents flow from the midlatitudes to the tropic seas, which enable the tropic coastal lands to enjoy a cool weather. (eg. Peru Currents) – The high latitude cold currents flow from mid latitudes to the high latitude areas which can lower down the temperature of the coastal lands. (eg. Labrador Current along the northern coast of Canada, and Oya Siwo Current along Japan Sea. )
World distribution of temperature w Average temperature
Jan. and July.
Jan. and July
World distribution of temperature w The annual march of insolation between the summer and winter solstices creates very different patterns. w The thermal effect of land sea distribution, and major ocean currents play an very important role on global temp. distribution. – There is a more pronounced migration and concentration of isotherms over land masses than over the ocean. – The annual range of temp. is greater in continental than in coastal locations. (max. 55 o. C at Siberia). – The large heat storage of the oceans cause them to be warmer on average in winter, but colder in summer than land in the same latitude. – The influence of main ocean currents is evident especially in winter (for warm currents) and summer (for cold currents) • Gulf Stream (Warm current) pushes the isotherms poleward in N. Atlantic in January (winter in N. hemisphere). • Peruvian current (Cold current) pushes equatorward displacement of isotherms along the coast of Peru and Chile in January (summer in S. hemisphere).
World temp. distribution – Jan.
World temp. distribution - July
Human Impact on the Atmospheric Energy w Human can alter the energy balance over different space and time-scales by deliberate or unconscious action with beneficial or harmful results. w The energy balance is altered by: – Changing the nature and composition of the air. – Altering the character of the earth’s surface. w Warming effects: – Urban heat island effect – Enhancing green-house effect – Such warming may cause rising sea level due to glacier melt. w Cooling effects: – Particulte emission may contribute to global cooling effect. – Human modification of the earth’s albedo (eg. by desertification), may also be responsible for planetary cooling.
Typical climatic changes (Urbanization)