How does equation (1) derived to equation (2) and (3)

Elements Of Electromagnetics
7th Edition
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Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
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How does equation (1) derived to equation (2) and (3)
• Evaporation of water stored in the soil or Condensation of atmospheric
water vapour onto the surface.
Each of these processes can be associated with an energy flux density.
Definition: Energy Flux Density The rate of transfer of energy normal to
a surface of unit area. The SI unit is J m 2 s¹ which is equivalent to W m-2.
The energy balance of a surface layer of finite depth and unit horizontal
area can be written as,
or
dQ
dt
= Rn - G - H − AE
. Q is the total heat energy stored in the surface layer.
● R is the net surface irradiance (commonly referred to as the net
radiation). It represents the gain of energy by the surface from radiation.
It is a positive number when it is towards the surface.
. G is the Ground Heat Flux. It is the loss of energy by heat conduction
through the lower boundary. It is a positive number when it is directed
away from the surface into ground. The value at the surface is denoted
Go.
.H is the Sensible Heat Flux. It represents the loss of energy by the
surface by heat transfer to the atmosphere. It is positive when directed
away from the surface into the atmosphere.
AE is the Latent Heat Flux. It represents a loss of energy from the
surface due to evaporation. (A is the specific latent heat of evaporation,
units J kg-¹ and E is the evaporation rate, with units kg m-2 s-¹).
1
(1)
For an infinitely thin surface layer the heat storage in Eq. 1 is zero and
reduces to,
Rn Go H XE = 0
Rn Go= H + XE
Bo=
(2)
The quantity R - Go is known as the available energy. In modelling the
surface energy balance we need to be able to calculate the available energy and
partition it between the sensible and latent heat fluxes.
H
XE
(3)
The way in which the available energy is partitioned between the sensible
and latent heat flux can be quantified by taking the ratio of the sensible to
latent heat flux, which is known as the Bowen ratio,
Transcribed Image Text:• Evaporation of water stored in the soil or Condensation of atmospheric water vapour onto the surface. Each of these processes can be associated with an energy flux density. Definition: Energy Flux Density The rate of transfer of energy normal to a surface of unit area. The SI unit is J m 2 s¹ which is equivalent to W m-2. The energy balance of a surface layer of finite depth and unit horizontal area can be written as, or dQ dt = Rn - G - H − AE . Q is the total heat energy stored in the surface layer. ● R is the net surface irradiance (commonly referred to as the net radiation). It represents the gain of energy by the surface from radiation. It is a positive number when it is towards the surface. . G is the Ground Heat Flux. It is the loss of energy by heat conduction through the lower boundary. It is a positive number when it is directed away from the surface into ground. The value at the surface is denoted Go. .H is the Sensible Heat Flux. It represents the loss of energy by the surface by heat transfer to the atmosphere. It is positive when directed away from the surface into the atmosphere. AE is the Latent Heat Flux. It represents a loss of energy from the surface due to evaporation. (A is the specific latent heat of evaporation, units J kg-¹ and E is the evaporation rate, with units kg m-2 s-¹). 1 (1) For an infinitely thin surface layer the heat storage in Eq. 1 is zero and reduces to, Rn Go H XE = 0 Rn Go= H + XE Bo= (2) The quantity R - Go is known as the available energy. In modelling the surface energy balance we need to be able to calculate the available energy and partition it between the sensible and latent heat fluxes. H XE (3) The way in which the available energy is partitioned between the sensible and latent heat flux can be quantified by taking the ratio of the sensible to latent heat flux, which is known as the Bowen ratio,
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