Environmental Engineering Reference
In-Depth Information
to forecast, but it makes a major contribution to
meridional energy transfer in mid to high latitudes
(see also
zonal index
.)
Run-off
See
moisture surplus
.
help of a
catalyst,
the
oxides of nitrogen
are broken
down into harmless
nitrogen
and
oxygen
.
sensible heat
Heat which can be felt or sensed, and
which causes the temperature of a body to change
shifting sands A popular image of desertification
in which desert sand dunes migrate into an area,
covering arable land and pasture and sometimes
settlements, thus creating a
desert
.
short-wave radiation
Radiation from the high energy
end of the
electromagnetic spectrum
. The term is
commonly applied to
solar radiation
which consists
of
ultraviolet
and
visible light
rays.
sink
Natural reservoir or store for materials circulating
through the earth/atmosphere system. The oceans
are a major natural sink for many substances from
heavy metals
to
carbon.
skin cancer
A disease indicated by the alteration of
skin cells and associated with damage to the genetic
make-up of the cells. Levels of skin cancer have
been rising since the late 1970s, apparently in
parallel with the thinning of the
ozone
layer, which
has allowed the
ultraviolet radiation
reaching the
earth's surface to increase. (See also
melanoma
.)
'slab' models
Interactive atmosphere-ocean circulation
models in which the ocean is represented by only
the uppermost layer or 'slab' of water. This is
necessary to accommodate the different response
times of atmosphere and ocean.
smog
A combination of smoke and fog which creates
atmospheric pollution.
soil erosion
The removal of
topsoil
by water, wind
and gravity at a rate greater than it can be formed.
soil moisture deficit (SMD)
A measure of moisture
availability used in drought evaluation. It
incorporates not only traditional elements such as
evapotranspiration
and
precipitation,
but also
considers the nature and state of crop
development—which influences moisture
requirements—and the storage capacity of the
specific soil.
soil moisture storage
Water held in the pore spaces of
the soil. In arid areas it offsets the
water deficit
caused when
evapotranspiration
exceeds
precipitation,
and delays the onset of
drought
.
When the soil moisture storage is full the soil is
said to be at
field capacity
.
soil structure
The form of the aggregates produced
when individual soil particles clump together.
Aggregates may be crumbs, blocks or plates, for
example.
S
Sahel
A semi-arid to arid area, subject to seasonal
and long-term drought, in Africa south of the
Sahara Desert. The Sahel proper consists of the
six nations, Senegal, Mauretania, Mali, Burkina
Faso, Niger and Chad, but the name has come
to include adjacent nations which suffer from
problems of
drought, famine
and
desertification
which are characteristic of the Sahel.
salinization
The build-up of salts in soils as a result of
the evaporation of
irrigation
water.
scrubbers
Structures used to reduce acid-gas emissions
from industrial plants. Wet or dry techniques can
be used, but all involve bringing the gases in contact
with alkaline or basic substances which neutralize
their acidity.
sea-ice models
Models which attempt to simulate the
role of sea-ice in global climates. They may be
incorporated in ocean models or coupled directly
to
general circulation models
.
sea-surface temperatures (SSTs)
A source of
information on potential change in the earth/
atmosphere system. Anomalous warming or
cooling of the sea surface, for example, may be
followed some time later by changing pressure,
wind and precipitation patterns. Once the initial
change has been identified such time-lags allow
subsequent events to be predicted.
seasonal drought
Regularly occurring
drought
restricted to one season of the year and offset by a
distinct rainy season. Seasonal drought is common
in the tropical and sub-tropical grasslands of Africa,
India and Australia where dry conditions are
brought on by the arrival of
continental tropical
air
as the
Intertropical Convergence Zone
advances
equatorwards.
secondary aerosols
Aerosols formed as a result of
chemical and physical processes in the atmosphere.
They are concentrated in the size range of 0.1-1
µm and may make up as much as 64 per cent of
total global aerosols.
selective catalytic reduction (SCR)
An efficient but
costly process developed to reduce the emission of
oxides of nitrogen
from power plants. With the
