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METEOROLOGYPrivate Pilot License
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REGULATIONS
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The atmosphere Heating process in the
atmosphere
Atmospheric pressure
The general circulation pattern
Pressure system
Wind
Local winds
Atmospheric stability
Temperature inversions
Clouds
Precipitation
Fog and Mist
Thunderstorms
Air masses and Fronts
Tropical Cyclones
Meteorological services
COURSE OUTLINE
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THE ATMOSPHERE
What is Atmosphere? is a mixture of gases, Nitrogen
and Oxygen
So, Meteorology is .
a study of atmosphere and its
various components and how
they interact.
Nitrogen 78.1%
Oxygen 20.9%
Argon 0.9%
Carbon dioxide, Methane,
Rare (inert) gases0.1%
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Vertical Division of the Atmosphere
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Troposphere
The troposphere is the first
layer above the surface and
contains half of the Earth's
atmosphere.W
eather occursin this layer.
From sea level to 20,000 feet
over the poles and up to
48,000 feet at the equator. At the top of troposphere is a
boundary known as
tropopause.
Jetstream and clear air
turbulence is located in this
region.
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Stratosphere
The atmospheric level
above the tropopause is
known as stratosphere.
It extends up to 160,000
feet.
Many jet aircrafts fly in the
stratosphere because it is
very stable. Also, the
ozone layer absorbs
harmful rays from the Sun.
At the top of stratosphere is
a boundary known as
stratopause.
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Mesosphere
Directly above the
stratosphere is the area
called mesosphere.
It extends up to the
mesopause boundary at
about 280,000 feet.
Meteors or rock fragments
burn up in the mesosphere.
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Thermosphere
After mesosphere, is
the another layer
called thermosphere.
The thermosphere is
a layer with auroras. It
is also where thespace shuttle orbits.
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Temperatures in the atmosphere
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Heating Processes in the Atmosphere
Radiation
Solar
Radiation
TerrestrialRadiation
Seasons Winter
Spring
Summer
Autumn
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This phenomenon is related to specific heat.
The ability of an object to heat up, cool
down or retain heat.
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Color of surface
Dark object tends to absorb more
of the suns rays resulting in more
heating.
Light objects reflects most of the suns
rays back to the atmosphere with very
little effect on the surface.
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Effect ofVariable Heating
It creates convection currents,
an important method of heat
transfer.
Hot air expanding becomeslighter and rises. This is an
example ofconvection.
Cool air from the sea moving
to replace the air that hasrisen. We call this as sea
breeze which is an example of
advection.
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Other factors affecting Variable
Heating Clouds
It diffuses solar radiation.
Wind
Its mixing effect affects
different air masses.
Coastal Proximity Temperature in areas near
coastline tend to be less
extreme.
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Atmospheric Pressure
Gas molecules in the atmosphereare constantly moving.
They exert a force on the object they
hit. This force is called atmospheric
pressure.
To measure such pressure, abarometeris used.
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ISA Temperature:
15rC at MSL, decreasing at
2rC/ 1000 feet
Effect of Altitude on Atmospheric
Pressure ISA Pressure:
1013.25hPa, decreasing at
1hPa/ 30 feet
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If air is thin, more speed is required to obtain enoughlift for takeoff, therefore takeoff roll is longer.
At higher altitudes, due to the decreased density of
air, aircraft engines and propellers are less efficient.
Aircraft Performance
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Atmospheric Circulation
Atmospheric circulation is the movement of air around the surfaceof the earth.
The Earth is curve, tilted, rotating and orbiting around the sunthus affecting the amount of heat striking the surface.
In theory, areas of low pressure exist over the equatorial regions
while high pressure exist over the polar regions.
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Solar heating causes air to become less
dense and rise in the equatorial region.
As the warm air flows towards the poles, it
cools, becoming more dense, and sinks
back to the surface. This movement isknown as Subsidence.
The circulation of air is modified by several
factors one of which is the rotation of the
earth. The force created by the earths
rotation is called Coriolis force.
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The Coriolis force deflects air to the right in
the Northern Hemisphere.
The amount of deflection differs depending
on the latitude.
The magnitude of the force depends alsoon the speed. The faster the speed, the
greater deviation.
The speed of the Earths rotation causes
the flow to break into 3 distinct cells in each
hemisphere - Hadley cell, Ferrel cell, Polarcell.
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Hadley cell
Ferrel cell
Polar cell
Circulation Pattern
Circulation patterns are further
complicated by seasonal changes,
difference between surfaces of
continents and oceans, and other
factors.
Frictional force caused by the
topography of the Earths surface
changes the movement of air in
the atmosphere.
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Surface Analysis Chart
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Low Pressure Area Lows are frequently associated with
stronger winds and atmospheric lift.
This lift will generally produce cloud
cover, due to adiabatic cooling, once
the air becomes saturated as it rises.
It turns counter clockwise in the
northern hemisphere.
Weather associated with LPA: The rising air in a low will cool and
cloud will tend to form.
Depending on the stability of air,
large CU, CB or NS cloud will form.
Rain or heavy showers.
Turbulence
Good visibility
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High Pressure Area H
igh pressure area is a region where theatmospheric pressure is greater than the
surrounding area. In some countries, these
regions may be referred to as anti-
cyclones.
Highs are frequently associated with light
winds and subsidence. Subsidence willgenerally evaporate most cloud droplets
after less than 500 meters, due to adiabatic
heating.
Weather associated with HPA:
The subsiding air in a low is stable.
As air descends and warms, any cloud
tends to disperse.
Poor visibility due to stable atmosphere.
Fine weather but hazy.
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Col
It is a region between twoH
PAs and twoLPAs.
It is an area of almost constant pressure
with isobars bending away from the center.
Weather associated with Col:
The wind is typically light and variable.
Fog is possible (during winter) and high
temperature (in summer).
Weather generally is unpredictable.
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Wind It is the flow of air in horizontal motion due to
the difference in pressure between two joining
air masses.
On a MSL Synoptic Chart, the isobars, which
joins lines of equal pressures, indicate both
wind speed and direction.
If the isobars are close together, wind isstrong. And the further apart the isobars the
weaker the wind.
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Local windsSea Breeze (A)
It is a wind from the sea that develops over
land near coasts.
It is formed by increasing temperature
differences between the land and water
which create a pressure minimum over the
land due to its relative warmth and forces
higher pressure, cooler air from the sea to
move inland.
Land Breeze (B) It occurs exactly opposite reason to sea
breeze.
At night, the land cools more quickly than
the sea.
The result is that the flow of air is now from
the land out to the sea.
Land breeze are strongest during the early
hours of the morning.
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Katabatic wind It is a wind that blows down a
mountain slope during the night and in
the early morning when the land loses
heat by radiation.
The land then cools the air in contact
with it and on a slope the dense air
mass slides down the slope under
the influence of gravity.
The katabatic wind speed depends on:
The size and steepness of the
mountain
How cloudy the sky is
Surface friction Length of the night
Anabatic wind The opposite of katabatic wind.
This less dense air flow up the slope.
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Mountain waves
When a wind flows towards a mountain
producing a series of standing waves. They are periodic changes of
atmospheric pressure, temperature and
orthometric height in a current of air
caused by vertical displacement.
They can also be caused by the surface
wind blowing over an plateau or even byupper winds deflected over a thermal
updraft or cloud street.
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Wind Shear
Refers to the variation of wind over
either horizontal or vertical distances,the difference in wind speed and
direction over a relatively short
distance in the atmosphere.
An additional hazard of turbulence is
often associated with wind shear.
It is commonly observed nearmicroburst and downburst caused by
thunderstorms, weather fronts, areas
of locally higher low level winds
referred to as low level jets, near
mountains, radiation inversions that
occur due to clear skies and calmwinds, buildings, wind turbines, and
sailboats.
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Wake Turbulence
The turbulence that is formed behind
an aircraft as it passes through theair. This turbulence includes various
components, the most important of
which are wingtip vortices and
jetwash.
These vortices are at its greatest
strength when the aircraft generatingis heavy, clean, and slow.
Wake turbulence is especially
hazardous during the landing and
takeoff phases of flight.
Wake turbulence generation begins
at rotation and ends at touchdown.
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Atmospheric Stability
As a parcel of air rises the pressure around it
reduces. Therefore as is rises, it will expand and it
will cool. The air is said to be cooling adiabatically.
Adiabaticmeans a change in temperature not due to
heat transfer but a change in pressure around its
surroundings.
The lapse rate is the change of atmospheric
temperature with height.
Environmental Lapse Rate
Adiabatic Lapse Rate
Definitions:
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When unsaturated air cool adiabatically at
approximately 3rC/ 100 feet, this is known as
Dry Adiabatic Lapse Rate (DALR).
When saturated air in a form of water vapor
changes to liquid, it gives off latent heat, it
slows down the adiabatic cooling process.
The air cools at a slower rate, this is called
Saturated Adiabatic Lapse Rate (SALR) at
approximately 1.5rC/ 1000 feet.
Adiabatic Lapse Rate
Refers to the actual change of temperature
with altitude for the stationary atmosphere.
The ELR at a given place varies from day today and even during each day.
As an average, the ICAO defines an ISA with
a temperature lapse rate of 1.98 rC/1,000 ftfrom sea level to 11 km (36,090 ft).
Environmental Lapse Rate
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Atmospheric stability is the airs resistance to any
disturbing effect.
The ability to resist the narrowing of the spread
between air temperature and dewpoint.
Atmospheric Stability
The lapse rate determines the atmosphere's
resistance to vertical motion, or stability.
If the lapse rate equals the DALR then there is
no resistance to vertical motion.
If the lapse rate is larger, or "more stable" the
atmosphere resists vertical motion.
An atmosphere in which the lapse rate is smaller
(more negative) than the DALR is "unstable" andtends to spontaneously mix.
The only region of the atmosphere which is
generally unstable is the layer immediately
above heated ground, in which thermals form.
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Temperature Inversion
It is a deviation from the normal change of
an atmospheric property with altitude (an
increase in temperature with height).
When there is an inversion, it indicates a
very stable atmosphere.
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Types of Inversion
Radiation Inversion
Occurs after an overnight cooling of the
ground which in turn cools the lowest
layer of the atmosphere.
Subsidence Inversion
Usually occurs when different density of
air in the atmosphere subside morecausing some adiabatic warming.
When a warm layer of air overlying
colder air occurs about 4000 to 6000
feet above the earths surface,
inversion sets in.
Frontal Inversion Movement of a cold front results in cold
dense air forcing warmer air aloft.
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Clouds
A cloud is a visible mass of droplets or frozen
crystals floating in the atmosphere above the
surface of the earth.
All clouds are divided into 3 groups based on
the height of theirbase.
High Clouds
Usually forms above 20,000 feet AGL and
form only in stable air.
They are made of ice crystals and pose
no real threat of turbulence or airframe
icing.
Typical high clouds are cirrus, cirrostratus,
and cirrocumulus.
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Mid-level Clouds
Usually forms between 6,500 feet AGL and
extends up to 20,000 feet AGL.
They are composed of water, ice crystals, andsuper-cooled water droplets.
Typical middle-level clouds include altostratus
and altocumulus.
Altostratus clouds can produce turbulence and
may contain moderate icing.
Altocumulus clouds, which usually form when
altostratus clouds are breaking apart, also may
contain light turbulence and icing.
Low Clouds
Low clouds are those that form near the Earths
surface and extend up to 6,500 feet AGL.
They are made primarily of water droplets, but can
include super-cooled water droplets that induce
hazardous aircraft icing.
Typical low clouds are stratus, stratocumulus, and
nimbostratus.
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Basic cloud types
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Precipitation from clouds
Drizzle
Consist of very small water droplets.This type of precipitation is
associated with stratus clouds.
Rain Large water droplets coming from
nimbostratus cloud. Also varying
degrees from stratocumulus andaltostratus clouds.
Showers Occurs as a sudden start and
stopping of precipitation with clear
breaks in between. These fall withvarying degrees of intensity from
cumulus, cumulonimbus and
altocumulus type of clouds.
Hail Usually occurs from large towering
cumulus and cumulonimbus type of
cloud.
Snow
Occurs when star shaped icecrystals develop within a cloud
before falling. This is most
commonly seen from the stratus
group of clouds.
Virga
This doesnt reach the ground, so its
not really precipitation. The rain falls
from the base of a cloud but
evaporates before it reaches the
ground.
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Fog and Mist Fog is a form of stratus cloud at low level
with the horizontal visibility down to below1000 meters.
If the visibility is 1000 meters or more,
then it is known as mist.
Basically fog forms by the same method
as cloud. Fog types are categorized
according to how they form.
Fog is one of the most frequent causes of
low visibility at airports and as such is a
significant hazard to aviation.
Fog forms when the difference between
temperature and dew point is generally
less than 2.5rC.
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Radiation fog
is formed by the cooling of land after sunset
by thermal radiation in calm conditions with
clear sky. The cool ground produces condensation in
the nearby air by heat conduction.
Radiation fogs occur at night, and usually
do not last long after sunrise.
Advection fog
Occurs when moist air passes over a cool
surface by advection (wind) and is cooled.
Wind is required to form advection fog.
Winds of up to 15 knots allow the fog to
form and intensify; above a speed of 15
knots, the fog usually lifts and forms low
stratus clouds.
Advection fog is common in coastal areas
where sea breezes can blow the air over
cooler landmasses.
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Steam fog
Forms when cold, dry air moves over
warm water. As the water evaporates,
it rises and resembles smoke. This type of fog is common over bodies
of water during the coldest times of the
year.
Low-level turbulence and icing are
commonly associated with steam fog.
It often causes freezing fog, or sometimes hoar frost.
Dispersal of fog
Sun light to warm up the earths
surface.
An increase in wind strength.
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Thunderstorms Thunderstorm is a form of weather
characterized by the presence of lightning and thunder.
It is a cumulus cloud that has grown
into a cumulonimbus.
For a thunderstorm to develop, it
needs the following:
An unstable atmosphere
Abundant moisture to feed
the cloud.
A trigger to start the air rising.
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Thunderstorm can be defined by the trigger that
starts the air rising:
Convective storms are caused by surfaceheating over land in summer.
Frontal storms are caused by cold front
forcing warmer air upwards.
Orographic storms are started by air rising
over a mountain.
Nocturnal storms occur over the ocean atnight and are caused by cooling at the top of
a large cumulus cloud.
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Life cycle of a thunderstorm
Cumulus stage ischaracterized by warm,
strong updrafts which may
be as fast as 4000 feet per
minute. No precipitation at
this stage.
Mature stage is
characterized by both
updrafts and downdrafts,
extremely turbulent.
Lightning and rain begins
at this stage.
Dissipating stage last stageof an active thunderstorm.
Both updrafts and downdrafts
mix weakens leaving a
continuous rain until the cloud
is empty.
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Air mass and FrontsAir mass
Is a large volume of air that havecharacteristics of temperature and
water vapor content.
Air masses cover many hundreds or
thousands of square miles, and
slowly change in accordance with the
surface below them. They have continental and maritime
source regions, with different
temperature and moisture
characteristics..
Groupings: Tropical maritime form over
warm tropical waters and bring
warm, moist air.
Tropical continental
Polar maritime forms over a
polar region and brings cool,
dry air with it.
Polar continental
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Cold front
Occurs when a mass of cold, dense, and stable air
advances and replaces a body of warmer air.
Cold fronts move more rapidly than warm fronts,
progressing at a rate of 25 to 30 m.p.h.
A typical cold front moves in a manner opposite that of a
warm front; because it is so dense, it stays close to the
ground and acts like a snowplow, sliding under the
warmer air and forcing the less dense air aloft.
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Prior to the passage of a typical
cold front, cirriform or towering
cumulus clouds are present, andcumulonimbus clouds are possible.
Rain showers and haze are
possible due to the rapid
development of clouds.
The wind from the south-southwest
helps to replace the warmtemperatures with the relative
colder air.
A high dewpoint and falling
barometric pressure are indicative
of imminent cold front passage.
As the cold front passes, towering
cumulus or cumulonimbus clouds
continue to dominate the sky. Depending on the intensity of the
cold front, heavy rain showers form
and might be accompanied by
lightning, thunder, and/or hail.
More severe cold fronts can also
produce tornadoes. During cold front passage, the
visibility will be poor, with winds
variable and gusty, and the
temperature and dewpoint drop
rapidly.
Temperature will fall and barometric
pressure begins to gradually
increase.
Before passage: After passage:
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Warm front
Occurs when a warm mass of air advances and
replaces a body of colder air.
Warm fronts move slowly, typically 10 to 25 miles per
hour (m.p.h.).
The slope of the advancing front slides over the top of
the cooler air and gradually pushes it out of the area.
Warm fronts contain warm air that often has very high
humidity. As the warm air is lifted, the temperature drops and
condensation occurs.
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Prior to the passage of a warm
front, cirrus, cirrostratus, altostratus,
nimbostratus are present. Thenstratus and fog.
Heavy continuous rain because of
rising of stable air forming stratiform
clouds or NS.
Wind from the south-southeast.
Cool temperature and steadilyfalling barometric pressure are
indicative of warm front passage.
Poor visibility.
Clouds starts to clear up.
Some light rain or showers.
Temperature starts to warm upwhile pressure slightly rise.
Before passage: After passage:
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Tropical Cyclone Cyclones are intense low pressure
systems that develop in tropical oceans. The main difference between cyclones
and other depressions is the destructive
winds which can reach speeds of up to
150 knots.
The main characteristics are:
They form between about 5 and 15latitude N.
They form over water whose
temperature is about 28C or warmer.
The lowest surface pressure is in the
eye. The strongest winds are around the
eye.
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Cyclone formation and track
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Meteorological ServicesAerodrome Forecasts (TAF)
A Terminal Aerodrome Forecast (TAF) refers to the forecast conditions
within a 5 NM radius of the center of an aerodrome or runway complex.
New format (TAF)
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Weather codes and translation
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JANDAKOT (YPJT)
TAF AMD YPJT 171043Z 1712/1806
25010KT 9999 LIGHT SHOWERS OF RAIN FEW015 BKN030
FM171700 21005KT 9999 SCT015FM180200 21013KT 9999 SCT030
PROB30 1719/1724 0300 FOG
RMK
T 19 18 16 15 Q 1015 1015 1015 1016
PERTH (YPPH)
TAF AMD YPPH 171040Z 1712/181825010KT 9999 LIGHT SHOWERS OF RAIN FEW015 BKN030
FM171700 21005KT 9999 SCT015
FM180200 21013KT 9999 SCT030
PROB30 1719/1724 0300 FOG
RMK
T 21 18 16 15 Q 1014 1014 1014 1015
HONG KONG (
VHHH)TAFVHHH 171100Z 1712/1818 15010KT 8000 FEW025 TX27/1807Z
TN19/1723Z BECMG 1715/1717 VRB05KT TEMPO 1718/1806 3000 HZ BR
BECMG 1802/1804 29010KT BECMG 1809/1811 12005KT
(TAF) samples
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Aerodrome Weather Reports (METAR)
A Aerodrome Weather Report (METAR) is a report of an actual observation
of weather conditions.
HONG KONG (VHHH)
VHHH 171100Z 1712/1818 15010KT 8000 FEW025 TX27/1807Z TN19/1723Z
BECMG 1715/1717 VRB05KT TEMPO 1718/1806 3000 HZ BR
BECMG 1802/1804 29010KT BECMG 1809/1811 12005KT
VHHH 171600Z 11006KT 060V160 9999 FEW015 23/18 Q1013 NOSIG
SINGAPORE (WSSS)
WSSS 171100Z 1712/1818 VRB05KT 9999 FEW018CB SCT020
TEMPO 1802/1806 4000 THUNDERSTORMS WITH RAIN SCT015CBBKN018
WSSS 171630Z VRB01KT 9999 FEW018 BKN300 27/25 Q1010 NOSIG
MANILA (RPLL)
RPLL 171100Z 1712/1812 12008KT 9999 SCT025 SCT100 TX31/1806Z TN24/1721Z
TEMPO 1712/1718 10005KT 8000 -RA SCT023 BKN090RPLL 171600Z 12006KT 8000 SCT023 BKN100 26/25 Q1012 NOSIG RMK A2989
LAPU-LAPU (RPVM)
RPVM 171100Z 1712/1812 04008KT 9999 FEW020 SCT100 BKN250
TEMPO 1712/1718 02006KT 9000 FEW018CBFEW020 BKN090
RPVM 171600Z 34004KT 9999 FEW020 BKN300 25/23 Q1011 A2985
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ATIS YPPH K 171616
+ APCH
:RWY: 21 AND 24 FOR ARR.
RWY 21 FOR DEP
OPR INFO: TWY LIMA 2 AND
CHARLIE 3, NOT AVBL DUE WIP.
DEP FREQ 118.7
WND: 230/8
VIS: GREATER THAN 10 KM
CLD: SCT035TMP: 19
QNH: 1015
Automatic Terminal Information Service (ATIS)
Is a continuous broadcast of recorded
non-control information in busier terminalareas.
ATIS broadcasts contain essential
information, such as weather information,
which runways are active, available
approaches, and any other information
required by the pilots, such as importantNOTAMs.
Pilots usually listen to an available ATIS
broadcast before contacting the local
control unit, in order to reduce the
controllers' workload and relieve
frequency congestion. The recording is updated when there is a
significant change in the information, like
a change in the active runway. It is given
a letter designation (e.g. bravo), from the
phonetic alphabet.
ATIS YMML W 171616
RWY 16 FOR ARRS.
RWY 27 FOR DEPSWND: 200/6
VIS: GREATER THAN 10 KM
CLD: BKN022
TMP: 13
QNH: 1018
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Example When the bicyclist runs over the nail, the air, having a higher pressure than
the outside air, will rush out. The air does work against the atmosphere asit rushes out from the tire. In doing this work of displacing the outside air,the air from the tire must use some energy. That energy comes from thekinetic molecular energy. The kinetic energy of the molecules from the tireslows and the temperature falls.
No heat has been added or removed from the system yet the expanding aircools.This process is called Adiabatic Cooling. It is also called ExpansionCooling.
This process is reversible.
If we took a pump to compress the air, as we would if we were filling the tire,
then the energy used to compress the air is used to increase the kineticenergy of the molecules. Compression warms the air.This process is called AdiabaticWarming.
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Example 1
if we raise a parcel of air from ground level to100 meters in height, the temperature willdecrease by 1rC. The parcel cools at a rate of1rC per 100 m or 10rC per km.
The parcel expanded and did work on itsenvironment!
Now, bring the parcel back down to thesurface. The environment did work on theparcel.
This is an adiabatic process and is reversible.
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Example 2:
If we use a moist parcel of air (RH = 100%)
The rising air cooled and produced condensation. Thecondensation released latent heat so the rising parcel
does not cool as rapidly with height as a dry parcel. Parcel cools only 0.6rC per 100 m (on average).
Moist adiabatic lapse rate = 0.6rC per 100 m.Remember -- This is an average lapse rate. The actualone varies!!!
If the moisture falls out of the parcel as rain, theprocess is not reversible.
Reversible only if no moisture has been removed!
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If we (somehow) lift the parcel: It will cool at the dry adiabatic lapse rate. The parcel
will find itself cooler than the environmental (sounding) temperature. At the same
pressure, a cooler parcel will be denser than the environment. Being denser, the
parcel will descend back to where it came from.
STABLE!
If we (somehow) lift the parcel: It will cool at the dry adiabatic lapse rate.
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If we (somehow) lift the parcel: It will cool at the dry adiabatic lapse rate.
The parcel will find itself warmer than the environmental (sounding) temperature.
At the same pressure, a warmer parcel will be less dense than the environment.
Being less dense, the parcel will ascend and move farther from where it came from.
UNSTABLE!
If we (somehow) lift the parcel: It will cool at the dry adiabatic lapse rate.
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The parcel will find itself at the same temperature than the environmental (sounding)
temperature.
Being the same density, the parcel will not be accelerated in any direction and will remain
where it is.
NEUTRAL STABILITY! -- Dry Neutral, orConditional Instability
Wh t t i th i i i ?
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What triggers the rising air?
Convection
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What triggers the rising air?
Frontal Lifting
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What triggers the rising air?
Converging surface winds
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Vertical Cross Section View
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Stretching Process
Vertical
stretching (like
by a strong
updraft) also
increases
rotation
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Splitting Process
Right Moving Supercell
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Right-Moving Supercell
Processes
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Storm Tilt Vertical wind shear
and buoyancygradients across thecloud act to tilt theconvective tower inthe downsheardirection. For agiven amount ofshear, a stronger,updraft will not tilt as
much as a weakerupdraft simplybecause its verticalmomentum isstronger.
Right Moving Supercell
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Right-Moving Supercell
Processes
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Additional Effect
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Temperature Inversions
What is an inversion?
An inversion is a stable zone in the atmosphere.
Inversions that are weak may only last a day
while strong inversions can stay around formultiple days until the weather changes. During
a strong inversion, pollution is trapped under this
cap, preventing exhaust like carbon monoxide
from vehicles and wood stoves to mix or rise upin the atmosphere.
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Temperature Inversions
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Change of state
Evaporation is the process by which
molecules in a liquid state (e.g. water)
spontaneously becomes a gas (e.g. water
vapor), without being heated to the boilingpoint. It is the opposite of condensation.
Generally, this manifests as the gradual
disappearance of the liquid, when exposedto a significant volume of gas.
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Change of state
Condensation is the change in matter of
a substance to a denser phase, such as a
gas (or vapor) to a liquid.[1] Condensation
commonly occurs when a vapor is cooledto a liquid, but can also occur if a vapor is
compressed (i.e., pressure on it increased)
into a liquid, or undergoes a combinationof cooling and compression.
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Change of state
Sublimation of an element or compound is the
change from a solid directly to a gas with no
intermediate liquid stage
Deposition is a process in which gas transforms into
solid. The reverse of deposition is sublimation.
One example of deposition is the process by
which, in sub-freezing air, water vaporchanges
directly to ice without first becoming a liquid.
This is how snow forms in clouds, as well as
frost and hoar frost on the ground.
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MOISTURE
Humidity is the amount ofwater vaporin air. Absolutehumidity, relative humidity, and specific humidity aredifferent ways to express the water content in a parcel ofair. Relative humidity is the most frequently used of
these expressions because of its importance in weatherforecasting.
Relative Humidity is a term used to describe theamount of water vapor that exists in a gaseous mixtureof air and water, expressed as a percentage of the
maximum amount of water vapor that could be present ifthe vapor were at its saturation conditions
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CALCULATING CLOUD BASES
Dewpoint- dew point of a given parcel ofairis thetemperature to which the parcel must be cooled, atconstant barometric pressure, forwater vaportocondense into water, called dew.
Cloud bases Unsaturated air 5.4 F/ 1000ft.
Dewpoint Temperature cools 1F/1000ft
4.5F/1000ft Converge
Temperature (F) Dewpoint (F) x 1000ft4.5F
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