Surface Energy Budget
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Transcript of Surface Energy Budget
Surface Energy Budget• R = - (G + H + L )• R = net solar and terrestrial radiation at the earth’s
surface (+ into surface)– Absorbed solar radiation (incoming – reflected)– Incoming longwave radiation emitted by gases and clouds in
the atmosphere– Outgoing longwave radiation emitted by the earth’s surface
• G- storage of energy into the deep soil (- into soil)• H – heat flux into atmosphere(- into atm)• L – Latent heat flux into atmosphere ( - into atm)
Heat StorageSpecific heat (j/(kg K)
Density (kg/m3) Heat storage per unit volume per K
Soil inorganic 733 2600 1.9x106
Soil inorganic 1921 1300 2.5x106
Water 4182 1000 4.2x106
Air 1004 1.2 1.2x103
Hartmann (1994)
Soil Temperature
• high intensity of solar radiation at high altitudes can result in high surface temperature
• Austria- 80C humus at 2070 m; air temp at 2 m 30C
• New Guinea 60C at 3480 m air temp 15C
Barry (1992)
Net Radiation
Whiteman (2000)
Surface Energy Budget
Whiteman (2000)
Surface Energy Budget
Whiteman (2000)
Solar Radiation
m
p/ps = fraction of atmosphere above point = 1
• m= 1/(sin()• m = non-dimensionaloptical depth at surface• m =1,
• m =2,
• m =4,
• When sun at 14o , light travelling through 4 atmospheres
Solar Radiation
M
p/ps = fraction of atmosphere above point
• M = m p/ps = non-dimensional optical depth at pressure p• At 500 mb (p/ps = .5):
•for zenith angle = 14o, equivalent to path length at sea level for zenith angle of 30o
• so, more radiation at higher elevation
Solar Radiation- Ideal Atmosphere
Pressure (mb) M=1;zenith angle= 90o
M=2; zenith angle= 30o
1000 mb 1233 W/m2 1136 W/m2
500 mb 1288 W/m2 1227 W/m2
Diff = 55 W/m2 91 W/m2
Solar radiation reduced in lower atmosphere by:
--absorption of radiation by water vapor
-- Mie scattering by aerosols
Barry (1992)
Absorbed Solar Radiation• Absorbed solar radiation depends strongly
on albedo: Abs Solar = Solar (1 – )• Snow cover reflects solar radiation and diminishes
absorbed solar radiation
• Annually, snow cover at high elevation later in season than in valleys tends to cause absorbed solar radiation to diminish with elevation
Whiteman (2000)
Incoming Longwave Radiation
Iijima and Shinoda (2002)
Outgoing Infrared Radiation
• Stefan-Boltzmann Law: IR = T4
• As elevation increases:– temperature decreases, IR radiation decreases– Optical thickness of atmosphere decreases (less
greenhouse gases, including water vapor), atmospheric transparency to outgoing radiation increases, more IR escapes
• Emissivity () of snow and ice is high
Whiteman (2000)
Infrared Radiation: December, Austrian AlpsAltitude (m) Bare ground
W/m2
Snow cover W/m2
200 289 301
1000 270 287
2000 255 274
3000 240 255
Barry (1992)
Net Radiation• Net Radiation =
Absorbed solar radiation + downwelling IR – IR
• Effect of altitude on net radiation is variable and depends most strongly on decrease with height of absorbed solar radiation
Barry (1992)
Peter Sinks
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-100
0.00
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-200
-100
0.00
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EXP2
Sept. 11Sept. 10Sept. 9 Sept. 12
QG
QNET
QH
EXP3
12 18 0 06 12 18 0 06 12 18 0 06 12Hour (MDT)
Clements (2000)
Radiation Budget on Slope
Temperatureslope
Temperature ground
solar
downwelling IR
IR
Variations in sunrise time
Whiteman (2000)
Influence of aspect (orientation)
Barry (1992)
Influence of aspect (orientation)
Barry (1992)
Influence of slope angle
Barry (1992)
Inclination angle, valley orientation,
season
South – north West - east
Whiteman (2000)
Microclimates
• Small topographic irregularities
• Differences in slope angle and aspect
• Types (Turner 1980)• Sunny windward slope (high radiation; high wind)
• Sunny lee slope (high radiation; low wind)
• Shaded windward
• Shaded lee
Microclimates
Barry (1992)