Geoscience Reference
In-Depth Information
Temporary perturbations
Perturbations in oceanic circulation
Oceans cover about two-thirds of the globe and are strongly coupled to the
overlying atmosphere through sea-surface temperature. Regular changes in sea-
surface temperature that occur annually in response to solar heating influence the
frequency of tropical storms. Changes at longer timescales such as occur in El
Niño and La Niña events or during the Pacific Decadal Oscillation (PDO) are
associated with consequential shifts in atmospheric circulation that influence
terrestrial hydrometeorology.
Perturbations in atmospheric content
Some important impacts of activity on continental surfaces arise indirectly through
associated changes in atmospheric constituents that participate in the process that
control radiation transfer through the atmosphere. Erupting volcano and natural or
human-induced atmospheric pollution can alter aerosol concentrations and
influence regional and global hydroclimate by altering the absorption of solar
radiation. Changes in hydroclimate also occur in response to natural or human-
induced changes in the concentration of the radiatively active gases such as carbon
dioxide that control the transfer of longwave radiation through the atmosphere.
Perturbations in continental land cover
The general contrast between the surface exchanges of oceanic and continental
surface can be modified by changes in continental land cover. Such changes alter
the albedo and hence solar radiation capture, the aerodynamic roughness of the
surface and hence momentum capture, and the partition of available energy
between latent and sensible heat fluxes. Changes in land cover may occur naturally
in response to changing climate, or they may result from large-scale intervention
that alters the vegetation present over land areas, such as deforestation.
Latitudinal imbalance in radiant energy
As discussed in Chapter 5, all the radiant energy entering the Earth system from
the Sun is within a spectrum that is determined by the temperature of the Sun and
is mainly in the wavelength range of 0.15 to 4
m. The intensity with which solar
radiation enters the top of the atmosphere is strongly determined by latitude, with
more arriving at the equator and less at the poles. On the other hand, most of the
energy leaving the Earth system is in the longwave, mainly in the wavelength
range of 3 to 100
μ
m. The spectrum and amount of outgoing radiation is
determined by the temperature of the surface of the Earth and overlying
atmosphere at the latitude at which the longwave radiation leaves. The temperature
μ
