3basics of meteorology
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hidroTRANSCRIPT
Hydrology I
Jozsef Szilagyi, Professor of Hydrology Department of Hydraulic and Water
Resources Engineering Budapest University of Technology and
Economics
Lecture #3: Basics of meteorologySimplified radiation balance of the earth’s land-atmosphere
system:Rc = solar constant (1367 W/m2)
Rscattered
Rdirect
αRc
Rthermal_up
Rthermal_down
Short-wave radiation Long-wave (thermal) radiation
Short-wave:
In: Rsc + Rd = Rc
Out: αRc
Balance(in – out):Rc – αRc = Rc(1-α)
Long-wave:
In: Rtd = εaσTa4
Out: Rtu = εsfσTsf4
Balance: Rtd – Rtu
ε is emissivity (close to 1) of the atmosphere (a) and the land surface (sf), respectively. It is defined as the ratio of energy radiated by the body over the energy radiated by a perfect black body at the same temperature. α is albedo (Rout/Rin), σ is the Stefan-Boltzman constant: 5.78·10-8 W / m2K4.
Net radiation (radiation balance): Net shortwave + net longwave Rn = Rc(1-α) + Rtd – Rtu (for a unit area)
Q1: Why are black cars hotter than white ones?Q2: Why is it that in the winter time (in the northern hemisphere) when the earth is closer to the Sun, it is colder than in the summer, when it is farther away from it?
30% 70%
Log-log scale
• Lab2: (a) What is the mean temperature of the earth’s surface? (b) What would be the same temperature without the presence of the atmosphere and greenhouse gases in it?
(a) Rn = Rc(1-α) + Rtd – Rtu, over a long-term the earth is in a radiation equilibrium (not considering the present climate change), thus Rn is zero. Therefore
0 = Rc(1-α)Acr + εaσTa4A - εsfσTsf
4A
= 1367(1-0.3)Acr + σ23344Acr - σ Tsf4 4Acr
where Acr is the cross-sectional area (this is what blocks the incoming radiation from the Sun) of the globe, while A is the surface area (=4Acr) of it.
(b) 0 = 1367(1-0.3)Acr - σTsf44Acr (Here we assume that the
albedo would be the same)
H
H
H
H
ITCZ in July
ITCZ in January