Transcript 2.1 Mist and Fog

Geography Cambridge AS level syllabus 9696
Mist & fog
page 27
Mist & fog are cloud at ground level
Overview
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Types of fog
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Advection fog
Radiation fog
Upslope fog
Evaporation (mixing) fog
Steam fog
Fog formation
(1) by cooling…air is cooled below its saturation
(2) by evaporation and mixing
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For fog to occur condensation must take
place near ground level
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Important concept in fog and cloud formation
Evaporation vs. Condensation
Advection fog
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Forms by condensation of warm, moist air
carried by winds over the cold coastal water
common along summertime coast
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Water near the coast is much colder than offshore
water (see upwelling in Ch.8) + onshore winds
Fog disappears as it is pushed inland by
onshore winds (due to evaporation)
Radiation fog
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Produced by the earth’s radiational cooling
Forms best on clear nights + shallow moist
air near the ground + light winds
Common over land in autumn and winter
Also called valley fog
Valley fog can persist for weeks unless cold
air moves in aloft or strong winds mix it up.
Burn off (of fog)
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Refers to dissipation of fog
Sunlight warms the ground → enhances
evaporation of fog and mixing of air
Geography Cambridge AS level syllabus 9696
Temperature inversions p28
The ‘Normal’ Situation
105’ 38°F
105’ 38°F
64’ 40°F
64’ 40°F
32’ 40°F
32’ 40°F
16’ 41°F
8’ 41°F
16’ 41°F
8’ 41°F
Temperature Inversions
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These are when the
‘normal’ situations are
reversed ie when
warmer air overlies
colder air.
This can be at low
level
Temperature Inversions
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These are when the
‘normal’ situations are
reversed ie when
warmer air overlies
colder air.
This can be at low
level or at high level
Temperature Inversions
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There is a natural
inversion in our
atmosphere as the
stratosphere is the
layer that absorbs
most of the ultraviolet
radiation (high level)
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See Figure 2.8
on p.28
Temperature Inversions
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High level inversions are also found in depressions,
when the warm sector overlies the cold sector
(occlusion)
Temperature Inversions
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Low level or ground
inversions occur in
anticyclonic conditions
when there is a rapid
loss of energy at night.
The air near the surface
is cooled by conduction
of heat to the cold
ground. The lower layer
is therefore colder than
the air above it.
Temperature Inversions
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Low level or ground
inversions occur in
anticyclonic conditions
when there is a rapid
loss of energy at night.
The air near the surface
is cooled by conduction
of heat to the cold
ground. The lower layer
is therefore colder than
the air above it.
Temperature Inversions
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A classic inversion is where the hot emissions
given off by industrial chimneys trap in the colder
air below (see figure 2.9 on page 28)
Signs of a surface
inversion in the
early morning
Lack of heavy cloud cover
Windless or light
variable wind
Ground Fog
Frost (or dew)
Smoke from a chimney forming a layer
Surface inversion - early morning
Definition of inversion
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In meteorology, an inversion is a deviation
from the normal change of an atmospheric
property with altitude. It almost always refers
to a "temperature inversion", i.e., an increase
in temperature with height, or to the layer
("inversion layer") within which such an
increase occurs.
Explanation of cause
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Under certain conditions, the normal vertical
temperature gradient is inverted such that the
air is colder near the surface of the Earth.
This can occur when, for example, a warmer,
less-dense air mass moves over a cooler,
denser air mass.
Consequences
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Temperature inversion stops atmospheric
convection (which is normally present) from
happening in the affected area and can lead
to the air becoming stiller and murky from the
collection of dust and pollutants that are no
longer able to be lifted from the surface. This
can become a problem in cities where many
pollutants exist. Inversion effects occur
frequently in big cities such as Barcelona.
Barcelona smog
http://www.joserodriguez.info/bloc/smog-anticiclones-y-politicaspublicas-en-barcelona
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Estamos sufriendo unos niveles de contaminación
bastante graves. La meteorología se ha conjurado
para que el aire contaminado de la ciudad no pueda
dispersarse (y llegar a otros lugares y así compartir
esa contaminación con el resto del mundo),
elevando los niveles de partículas en suspensión y
gases contaminantes por encima de los niveles que
recomienda la OMS.
Que de tanto en tanto las ciudades sufren SMOG es
algo que hay que saber que ocurrirá. No por
menos en Barcelona mueren más de 3.500
personas al año por problemas respiratorios
asociados a esta contaminación.