Transcript Major Forms of Condensation

Major Forms of
Condensation
What are the forms of
condensation?
 Cloud
 Fog
 Frost
and Dew
Differences between Forms of
Condensation
 Cloud,
fog, frost and dew??
– Cloud
– fog
the
– frost and dew
the earth
high in the sky
near the surface of
earth
at the surface of
Similar in Formation
 Cooling
(Temperature drops)
 Air holds less water
 RH increases
 When RH = 100%, moisture
released
Frost at 22/12/1999
FROST & DEW
Frost again
Dew at Spider Web
What is the difference
between Dew and Frost?
–Dew: dew point > 0C
–Frost: dew point  0 C
FOG
Radiation Fog (Conditions)
 Clear
sky
 high RH
 temperature inversion
 calm and still air
 presence of depression or hollow
Advection Fog
Advection Fog
Frontal Fog
Steam Fog
Upslope Fog
CLOUD
Precipitation
 Water
droplets from condensation
is very small in size – 0.1 mm
 Raindrops are much larger – 0.52.0 mm
 The main difference between
condensation and precipitation is
the size of water droplets
Formation Processes
 Air
cooling
 Condensation and cloud formation
 Accumulation of moisture
 The growth of cloud droplets
Collision and Coalescence
 In
tropical and sub-tropical regions
 Cloud top temperature :
 warmer than -15oC
 Turbulence Mixing :
 Different size droplets move at different
speeds
 cumulonimbus
Collision and Coalescence
Fall in
higher
speed
Fall in
lower
speed
wake
capture
Large
Water
droplet
Direct
capture
Ice-Crystal (Bergeron) Process
 In
higher latitudes (temperate regions)
 Super-cooled water – water droplets in
cloud with temperature below 0oC
 Because of extremely small size of
cloud droplets
 Insufficient freezing nuclei
Ice-Crystal (Bergeron) Process
 Saturated
vapour
pressure over
super-cooled
water is
greater than
that over ice
Ice-Crystal (Bergeron) Process
 Air
can be
saturated for
ice when it is
not saturated
for water
Ice-Crystal (Bergeron) Process
 Ice
crystals
grow at the
expense of
cloud droplets
until they are
large enough
to fall
3 main types of precipitation
Convection
Rain
Lifting
mechanism
Real world
examples
Diagram of
formation
Cyclonic / Orographic
Frontal rain / relief rain
Low pressure Warm air
system due to mass meets
thermal nature cold air mass
ITCZ
Polar front
Uplifting
along
slopes
Tai Mo
Shan
Spatial Variation of rainfall
 There
is more
precipitation in
ocean than in
continent.
ocean
continent
Spatial Variation of rainfall
 Primary
maximum
occurs at a belt
between 10oN
to 10oS in the
vicinity of the
ITCZ
ocean
continent
Spatial Variation of rainfall
 secondary
maximum
occurs at a belt
between 40o to
55oN&S in the
vicinity of the
ITCZ
ocean
continent
Spatial Variation of rainfall
 Primary
minima
find in latitudes
higher than
55oN&S
 Secondary
minima in subtropical high
pressure belts
(20o-35oN&S)
ocean
continent
Factors affecting the pattern of rainfall
 Air
pressure
 Zones of convergence and divergence
 Strong convection along low pressure
belts
 Uprising air leads to condensation and
cloud formation
 Descending air along high pressure
belts suppress condensation
 Describe
and
explain the
factor that
influence the
pattern of rainfall
from the
diagram on the
right.
50oN
0o
50oS
Zones of abundant rainfall
 Around
the equatorial regions
 e.g. Amazon Basin
 Doldrum low pressure
 Convergence of trade winds along
ITCZ
 Intense solar radiation promotes strong
convective uplift
 Ares dominated by warm moist
equatorial marine air masses
Zones of abundant rainfall
 Western
sides in middle latitudes
 e.g. Western Coast of Canada
 Under influences of the onshore
westerlies and frequent frontal
cyclones
 Western mountrains(Rockies and
Andes) promote orographic influences
and heavy precipitation
 Describe
and
explain the
factor that
influence the
pattern of rainfall
from the
diagram on the
right.
Zones of scanty rainfall
 Polar
areas of North America
 Air with low moisture content due to
low temperature
 Descending cold upper air masses
unfavourable for condensation
Zones of scanty rainfall
 15o-30oS
in the western side of South
America
 30o-40oN of south-western U.S.A.
 Affected by sub-tropical anticyclone of
high pressure
 Rain-shadow effect of Rockies and
Andes