Environmental Engineering Reference
In-Depth Information
least 50 years and the elements of the model—such
as cold front, warm front, warm sector—remain
very much part of the current weather forecasting
vocabulary.
models
Idealized, and usually simplified,
representations of complex phenomena, models are
used to describe and explain as well as forecast the
effects of change. Models have been used
extensively in attempts to unravel the complexity
of the earth/ atmosphere system. (See also e.g.
carbon cycle models, climate models, coupled
models, coupled ocean/atmosphere, general
circulation models
.)
moisture deficit
In theory a moisture deficit exists in a
region when
evapotranspiration
exceeds
precipitation
. However, all soils have the ability to
store moisture which will offset the effects of any
deficit. As a result, a true deficit may not exist until
the soil water storage has been used up, and for
most practical purposes—drought evaluation, for
example—the focus is on
soil moisture deficit
(SMD)
rather than the simple relationship between
precipitation
and
evapotranspiration
.
moisture index
A representation of moisture
availability in an area, often used in
drought
and
aridity
studies. Most indices incorporate a
combination of meteorological elements including
precipitation, evapotranspiration, solar radiation,
temperature and wind speed.
moisture surplus
A moisture surplus exists in a region
when
precipitation
exceeds
evapotranspiration,
and
when the
soil moisture storage
is full. Any
additional precipitation will flow across the surface
as
run-off into
rivers and lakes.
molecule
The smallest part of a compound which
retains the composition and chemical properties
of the compound.
Montreal Protocol
An agreement reached in
Montreal, Canada in 1987 aimed at reducing the
destruction of the
ozone
layer. The signatories
agreed to a 50 per cent cut in the production of
chlorofluorocarbons
by the end of the century.
nitrogen and one of
oxygen
. An important natural,
ozone destroying gas responsible for perhaps as
much as 50-70 per cent of the natural destruction
of
stratospheric ozone,
through a long catalytic
chain reaction.
nitrifying bacteria
A group of bacteria found in soil
and in the root nodules of
leguminous plants,
which
are capable of fixing the atmospheric
nitrogen
essential for the creation of the complex nitrogen-
based compounds found in all forms of life.
nitrogen
A colourless, odourless gas which makes up
about 78 per cent of the volume of the
atmosphere
.
Molecular nitrogen is inert and may be considered
as a dilutant for the oxygen with which it shares
most of the atmosphere. When it does combine with
oxygen it forms
oxides of nitrogen,
a group of gases
involved in a number of current environmental
problems.
nitrogen dioxide (NO
2
)
A red-brown toxic gas, in which
each
molecule
consists of one
atom
of
nitrogen
and
two of
oxygen.
It is a major constituent of
automobile exhaust gases and a common
component of urban
photochemical smog
.
nitrogen oxides see
oxides of nitrogen
.
nitrous oxide (N
2
O)
One of the
oxides of nitrogen
in
which each
molecule
consists of two
atoms
of
nitrogen
and one of
oxygen.
Nitrous oxide is a
naturally produced
greenhouse gas,
but owes its
current growth to the increased use of agricultural
fertilizers and the burning of
fossil fuels
.
nomadism
A way of life in which groups of people move
from place to place in search of food for themselves
or their animals. Before the development of
agriculture, nomadic hunting groups were the norm.
normals (climate)
Data representing average climatic
conditions. Usually calculated over a thirty-year
period.
North American Water and Power Alliance
(NAWAPA)
A scheme to divert Canadian rivers,
flowing into the Arctic Ocean, southwards into the
United States, by means of a continental-scale
network of reservoirs, canals, aqueducts and
pumping stations. The main purpose of the scheme
was the provision of water for irrigation and
municipal supply in the arid west and southwest
of the United States. It was not developed beyond
the planning stage.
nuclear autumn (fall)
see
nuclear winter
.
nuclear winter
The result of rapid cooling brought on
by increased
atmospheric turbidity
and reduced
N
natural environment
see
environment
necrosis (of leaf tissue)
The disintegration of leaf tissue
caused by the degeneration of cells in direct contact
with
acid precipitation
.
nitric oxide (NO)
One of the
oxides of nitrogen,
in
which each
molecule
consists of one
atom
of
