Atmosphere Atmosphere

Part I

Energy

Contents 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

Atmosphere consists of a mixture of various gases surrounding the earth to a height of many km.

Meteorology deals with the physics of this atmosphere

Composition of Air

Permanent Gases– They always keep in a fixed proportion in the

atmosphere.

Changing Gases– They are changing in difference places and time.

Solid Impurities

Permanent Gases

Changing Gases

Generally speaking, they are carbon dioxide (CO2), Vapour (H2O) and Ozone (O3).

CO2:

– 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 CO2 is the combustion of fossil fuel such as Coal, Oil, Gas,….

Changing Gases - 2 H2O :

– The proportion of H2O in the atmosphere is about 0-4% (Various in difference places).

– The source of H2O is evapo-transpiration from plants and water bodies .

– 50-60% H2O is distributed over the land 1.5km-2.5km.– It is fundamental to many essential meteorogical processes a

nd all weather phenomena. O3

– It is distributed in the Ozone layer (over land 20-25km) in the Stratosphere.

– It absorb most short wave radiation from the universe and protects the living bodies of the earth.

Others:– They are present in extremely minute percentages.

Changing Gases -3

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 for forming

water droplets.

Structure of the Atmosphere

Troposphere

Its thickness approximately 8 km (polar region) to 16-19 km (equatorial region).

Almost all weather phenomena, 75% of total mass of air, virtually all water vapour and aerosols are in this zone.

Vertical turbulence are most marked. With Environmental Lapse Rate (-6.5oC/km) Ceiling of the troposphere is called tropopau

se.

Stratosphere

From the tropopause to about 50km. The lower layer is isothermal layer. Cirrus clouds occasionally form in the lower

stratosphere. Isothermal layer terminates at a height of ab

out 20km and replaced by a inversion layer (temperature increase with height)

At the stratopause, a reversal to falling temperature sets in.

Mesosphere and Thermosphere

Mesosphere– From the stratopause to 80km.– Temperature falling with height.– Ceiling is called mesopause.

Thermosphere– From the mesopause to space (no well-defined u

pper limit).– Temperature increase with height.

Energy System Atmos. is open energy system. It receives energy from both directions (earth and s

un). Compared with sun (solar energy), earth’s energy c

an be negligible. All life processes and all exchanges of matter and e

nergy between the earth’s atmos. and the surfaces of the oceans and lands are driven by solar energy.

The planetary circulation systems of atmos. and oceans are also driven by solar energy.

Water changes in various forms (liquid, solid and gas) over the globe also driven by solar energy.

Sun is the energy source of the earth.

Energy Input – Solar Radiation

Importance– It is a electro-magnetic wave energy radiating fr

om 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

Nature:– Emitted from sun (surface temperature 6000oC)– It is a spectrum (combination energy of different

wavelengths)– Most of it is visible light rays (short-wave)– Energy emitted by earth (surface temp. 15oC) is

terrestrial radiation (long-wave)– Higher temperature of an object emits shorter-

wave of radiation.

Spectrum of solar rays

Spectrum of solar rays - 2 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.

Long-wave radiation (wavelength > 0.8 micron)– Infrared, micro waves and radio waves

– They are also absorbed by ozone, CO2 and clouds.

Spectrum of solar rays - 3

Energy Transfer within the earth

Receipt of solar radiation at the top of the atmosphere.

Receipt of solar radiation at the earth’s surface.

At the top of the atmosphere

Four factors– Solar output– Distance between the sun and the earth– Angle of solar incidence– Length of daytime.

Four factors 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.

Distance from the sun– Perihelion: closest to the sun (147.3 million km) on 3rd

January.– Aphelion: farthest to the sun (152.1 million km) on 4th

July.– 7% of the total energy difference.– Solar constant: 1.9 cal/cm2/min. or 2 cal/cm2/min.

Four factors 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 - LatitudeSolar incidence various between different latitudes of the earth surface.

Angle of incidence – Time of day

The angle of incidence increases from sunrise to a maximum during noon-time.

It decreases in the afternoon to another minimum during sunset.

Angle of incidence - Seasons Because of the occurrence of rotation, revolution and the

tilted of earth axis (66.5o to the horizontal), the mean angle of solar incidence a any place is constantly changing.

Angle of incidence – Length of daytime

The longer the daytime (time between sunrise and sunset) , the more solar radiation is received.

At the earth’s surface Solar energy received at the earth surface is much less than

that received at the top the atmosphere. It is due to the effects of the atmos., cloud cover, different s

urface covers, latitudes, elevation and aspect.

At the earth’s surface - 1 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 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 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

Table of albedos

At the earth’s surface - 4 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 Effect of elevation and aspect

– In middle latitudes, the intensity of incident solar radiation increases by 5-15% for each 1000m increase in elevation in the lower troposphere.

Energy Budget / Heat Budget

Energy Budget / Heat Budget -1 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, CO2.

• 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)• About18 units absorbed by surface indirectly (ASi)• About6 units scattering from the atmosphere (Si)

Energy Budget / Heat Budget - 2

Terrestrial Radiation (Long-wave radiation)– The surface receives about 77 units from atmos. Throug

h counter-radiation (CR).– About 8 units are lost directly back to space through At

mospheric 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

Green House Effect:– The atmosphere is largely heated from earth’s surface a

nd 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 counter-radiation.

– 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

Variation in Receipt of Heat Energy– The receipt of heat energy is very unequal geogr

aphically.– Near the equator, about 50% of the insolation re

aches 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 40oN to 30oS is the region of surplus. Two high-latitude regions of deficit. Energy balance can be maintained only if heat is transported from low-

latitude surplus belt to high-latitude deficit regions. The rate of meridional heat transport is greatest in middle latitudes.

Horizontal Heat Transport - 2

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 35o and 45o in both hemispheres.– Latent heat transport almost occurs in the lowest

2 or 3 km.– Sensible heat has a double maximum not only la

titudinally but also in the vertical plane.

Horizontal Heat Transport - 2

Horizontal Heat Transport - 3

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 Warm Currents refer to the sea water from low latit

ude areas to high latitude areas.– Eg. Gulf Stream, Kuro Siwo Currents.

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.

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 Cold Currents refer to those moving from high latit

ude areas to low latitude areas. Two categories

– The low latitude cold currents flow from the mid-latitudes 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 Average temperature

Jan. and July.

Jan. and July

World distribution of temperature The annual march of insolation between the summer and wi

nter solstices creates very different patterns. The thermal effect of land and sea distribution, and major o

cean currents play an very important role on global temp. distribution.– There is a more pronounced migration and concentration of isother

ms over land masses than over the ocean.– The annual range of temp. is greater in continental than in coastal l

ocations. (max. 55oC at Siberia).– The large heat storage of the oceans cause them to be warmer on av

erage 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. Atla

ntic in January (winter in N. hemisphere).• Peruvian current (Cold current) pushes equatorward displacement of is

otherms 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

Human can alter the energy balance over different space and time-scales by deliberate or unconscious action with beneficial or harmful results.

The energy balance is altered by:– Changing the nature and composition of the air.– Altering the character of the earth’s surface.

Warming effects:– Urban heat island effect– Enhancing green-house effect– Such warming may cause rising sea level due to glacier melt.

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)