368
E. M. Koriesh and I. H. Abo-Soud
8.3 Shortwave and Longwave Radiation
Profound changes in vegetation composition in the Arctic tundra have been observed
and are predicted in a warmer future climate. Shrub expansion may positively feedback to climate warming by decreasing the shortwave albedo. In Canadian studies
[87], they measured an average transmission of 36% of the incoming shortwave radiation below dwarf shrub (Betula nana), the transmission of wet sedge (Eriophorum
angustifolium) was 28%.
Global warming can be affected by shortwave and longwave radiation. Results of
Donohoea et al. [88] suggest that, although greenhouse gas forcing predominantly
acts to reduce outgoing longwave radiation, the resulting global warming is likely
caused by enhanced absorbed solar radiation. They added that global conservation
of energy is a powerful constraint for understanding Earth’s climate and its changes.
Variations in atmospheric composition that result in a net positive energy imbalance
at the top of atmosphere drive global warming, with the world ocean as the primary
reservoir for energy accumulation. In turn, increasing global surface temperature
enhances emission of longwave (LW) radiation to space. Anthropogenic radiative
forcing is dominated by LW active constituents, such as CO 2 and methane, and
shortwave (SW) forcing agents, such as sulfate aerosols (used for a suspension of fine
solid particles of a sulfate or tiny droplets of a solution of a sulfate [89]), are thought
to be acting to reduce absorbed solar radiation compared with their preindustrial
levels. Reduced outgoing longwave radiation, thus, seems the likely cause of the
observed global energy accumulation, although the limited length of satellite TOA
radiation measurements precludes determination of the relative contributions of ASR
and OLR by direct observation [90].
Trees in the urban area strongly reduce pedestrian level heat stress by absorbing
and reflecting solar irradiance although air temperature reduction effect is weak.
Modeled results are verified by measuring shortwave radiation under trees and roof
of the adjacent building [91].
Absorption profiles of incoming solar radiation determine incoming fluxes
between vegetation-covered ground and the atmosphere. Model calculations demonstrate significant deviations of absorption profiles from an exponential distribution in
the near-IR spectral region and high dependence of profiles on foliage orientation and
the solar zenith angle. The set of input parameters of the model coincides with that
of the Nilson-Kuusk canopy reflectance model. These parameters can be estimated
from remote measurements [92].
E. M. Koriesh and I. H. Abo-Soud
8.3 Shortwave and Longwave Radiation
Profound changes in vegetation composition in the Arctic tundra have been observed
and are predicted in a warmer future climate. Shrub expansion may positively feedback to climate warming by decreasing the shortwave albedo. In Canadian studies
[87], they measured an average transmission of 36% of the incoming shortwave radiation below dwarf shrub (Betula nana), the transmission of wet sedge (Eriophorum
angustifolium) was 28%.
Global warming can be affected by shortwave and longwave radiation. Results of
Donohoea et al. [88] suggest that, although greenhouse gas forcing predominantly
acts to reduce outgoing longwave radiation, the resulting global warming is likely
caused by enhanced absorbed solar radiation. They added that global conservation
of energy is a powerful constraint for understanding Earth’s climate and its changes.
Variations in atmospheric composition that result in a net positive energy imbalance
at the top of atmosphere drive global warming, with the world ocean as the primary
reservoir for energy accumulation. In turn, increasing global surface temperature
enhances emission of longwave (LW) radiation to space. Anthropogenic radiative
forcing is dominated by LW active constituents, such as CO 2 and methane, and
shortwave (SW) forcing agents, such as sulfate aerosols (used for a suspension of fine
solid particles of a sulfate or tiny droplets of a solution of a sulfate [89]), are thought
to be acting to reduce absorbed solar radiation compared with their preindustrial
levels. Reduced outgoing longwave radiation, thus, seems the likely cause of the
observed global energy accumulation, although the limited length of satellite TOA
radiation measurements precludes determination of the relative contributions of ASR
and OLR by direct observation [90].
Trees in the urban area strongly reduce pedestrian level heat stress by absorbing
and reflecting solar irradiance although air temperature reduction effect is weak.
Modeled results are verified by measuring shortwave radiation under trees and roof
of the adjacent building [91].
Absorption profiles of incoming solar radiation determine incoming fluxes
between vegetation-covered ground and the atmosphere. Model calculations demonstrate significant deviations of absorption profiles from an exponential distribution in
the near-IR spectral region and high dependence of profiles on foliage orientation and
the solar zenith angle. The set of input parameters of the model coincides with that
of the Nilson-Kuusk canopy reflectance model. These parameters can be estimated
from remote measurements [92].