Presentation on theme: "AL Energy Budget ` Recap zWhen solar radiation reaches the earth, the incoming solar radiation being yreflected yscattered yabsorbed zWhen it reaches."— Presentation transcript:
AL Energy Budget `
Recap zWhen solar radiation reaches the earth, the incoming solar radiation being yreflected yscattered yabsorbed zWhen it reaches the ground, some is being reflected (shortwave radiation). zThe ground converts the insolation into longwave outgoing radiation.
Recap (What’s more) zCounter-radiation by the clouds zSensible heat transfer zLatent heat transfer
Assumptions zScale:Global scale zTime:Long term trend
Division of Components ATMOSPHERE EARTH Earth-atmosphere
Operation of Energy Budget
The incoming solar radiation Total100 Scattered to space5 Scattered to ground6 Reflected by cloud21 Reflected from ground6 Absorbed by atmosphere15 Absorbed by cloud3 Absorbed by ground50
The outgoing radiation Total Sensible heat transfer9 Latent heat transfer20 Ground radiation absorbed by atmosphere 90 Ground radiation to space8 Radiation to the space60 Counter-radiation to the ground77
The outgoing radiation
Energy Budget Table zFormulate three energy budget tables according to the three different components: yearth system yatmospheric system yearth-atmospheric system
Heat balance at the ground surface Gain The balance of gain Loss The balance of loss Short-wave radiation from the sun 50 Counter-radiation from the atmosphere Long-wave radiation to the space 8 Long-wave radiation to the atmosphere 90 Latent heat flux to the atmosphere 20 Sensible heat flux to the atmosphere 9 127
Heat balance at the atmosphere Gain The balance of gain Loss The balance of loss Short-wave radiation from the sun Long-wave radiation from the ground 90 Latent heat flux from the ground 20 Counter-radiation to the ground 77 Sensible heat flux to the space Long-wave radiation to the space 60
Annual Solar Radiation at Earth Surface
Latitudinal distribution of solar radiation zThe annual solar radiation received along the equator is very high but not the highest zDue to the presence of cloud cover ( ITCZ) zInter-tropical Convergence Zone zBetween 10 o -20 o N and S, there receive most solar radiation zThe angle of incidence is high zLack of cloud cover
Latitudinal distribution of solar radiation zAt high latitudes, there is less radiation zBecause the angle of incidence is low zHigh albedo because of snow cover zMore insolation in Northern Hemisphere zBecause there is more land surface and less cloud cover
Global Distribution of Short Wave Radiation
Latitudinal Distribution of Annual Solar Radiation
Global Distribution of Long Wave Radiation
Global Distribution of Net Radiation
Annual Net Radiation
Difference between Figure 2.13 and 2.15 zFig shows annual solar radiation but Fig shows the net radiation zAnnual solar radiation considers incoming solar radiation only zNet radiation is nthe difference between incoming solar radiation and outgoing solar radiation.
TWO characteristics in spatial variation zThe net radiation amount of ocean is greater than land at the same latitude. zNet radiation decreases with increasing latitude.
Difference between S. Hemisphere and N. Hemisphere zThe net radiation amount at equivalent latitudes in the S. Hemisphere is more than the N. Hemisphere zbecause there are more ocean, zthen there is more cloud cover.
Variation in Average Annual Net Radiation
zAt nearly all latitudes, net radiation of the earth surface is above zero. zEnergy deficit is experienced at most latitudes of the atmomsphere system and stable over latitudes. zThe net radiation of the earth-atmosphere system is the combination of earth surface and atmosphere system zEnergy Surplus in between 0 o and 40 o N & S zEnergy Deficit in regions higher than 40 o N & S
Seasonal and latitudinal effect on Energy Budget SummerWinterTotal Equator Around 20 o 35 o -40 o N&S Polewards of about 65 o N&S surplus deficit surplus balance deficit
Relaxation of Assumptions
Illustration of the atmospheric energy budget
Description zIncoming solar radiation may be reflected and absorbed by clouds. Scattered and absorbed by atmosphere, reflected and absorbed by earth’s surface zShort-wave solar radiation reflected by clouds and earth’s surface may go back to space zShort-wave solar radiation scattered by atmosphere may go either to space or to the earth’s surface
Description zRadiation (both short-wave and long-wave) absorbed by clouds and atmosphere will eventually go to space or the earth’s surface in form of long-wave radiation zRadiation (both short-wave and long-wave) absorbed by earth’s surface will go back to space or atmosphere in form of log-wave radiation; or may be dissipated through latent heat loss or sensible heat loss to atmosphere
Heat transfer zShort wave radiation from the sun received by the earth leaves the atmosphere in the form of long-wave radiation and heated up the atmosphere zFor the earth as a whole, the amount of short wave-radiation received will be equal to the amount of long-wave radiation lost as to keep the earth at the same temperatures in the long run
Heat transfer zThe amount of short wave radiation received by the earth varies greatly along latitude and between seasons because of the earth’s spherical shape, the inclination of the axis, different amount of cloud cover and albedo of the earth’s surface zThe amount of long wave radiation leaving the atmosphere at different latitude does not vary as great as the amount received and thus resulting surplus of heat in the lower latitudes and a deficiency of heat in the higher latitudes.
Heat transfer zTo maintain an equilibrium, surplus heat from the low latitudes is transported to high latitude zHeat from lower altitudes is transport to higher altitudes zBoth horizontal and vertical transfer are involved zAtmospheric processes such as air circulation, condensation and precipitation are involved
Heat transfer zSince air is a poor conductor, conduction is unimportant in the atmosphere, but it is important in the ground zThe low viscosity of air and its consequent ease of motion makes convection the chief method of atmospheric heat transfer zHeat energy transferred by radiation becomes sensible heat only when absorbed by water vapour, carbon dioxide or ozone
Energy budget it tropical rainforest TRF zDue to high angle of incidence there is high incoming solar radiation, causing hot climate zAlbedo of forest-covered surface is low zSmall variation in length of daytime leads to little seasonal variation of incoming solar radiation producing uniform climate, small annual range of temperature and even distribution of precipitation
Energy budget it tropical rainforest TRF zLarge amount of radiation absorbed by earth’s surface, causing intense convection (latent heat loss), resulting abundant precipitation throughout the whole year zAbout 20% incoming solar radiation reflected by clouds. Preventing extreme high temperature in daytime
Energy budget it tropical rainforest TRF zMore than half of long-wave radiation from the earth’s surface absorbed by clouds and then re-radiated back to earth’s surface, keeping warm temperature in night time zTherefore, daily temperature range is also small