Meteorology 2
Quiz Wednesday, 18th
five slide review first
Atmosphere Composition
and Properties
10 0 %
Atmosphere has weight
– 14.7 psi @ sea level or 1013.2 mb
– Half of it is below 18,000 feet
– No well defined upper surface but
satellite drag data indicates
some air at 1,000 miles
– Gases each contribute to
Oxygen
21%
atmospheric pressure
Water/Other 1%
– Water vapour usually less
Nitrogen
78%
than 1% but can be 3.5%
90%
80%
70%
60%
50%
40%
30%
20%
10 %
0%
Vertical Structure
THERMOSPHERE
IONOSPHERE
3000 ° C @700km
MESOPAUSE
MESOSPHERE
STRATOPAUSE
STRATOSPHERE
TROPOPAUSE
TROPOSPHERE
SEA LEVEL
KM
120
110
100
Vertical Structure
-108
90
275,000 feet
80
70
60
-2.5
165,000 feet
50
40
30
20
36,089 feet
10
0
-110
-100
-90
-80
-70
-60
-56.5
-50
-40
-30
-20
-10
0
10
20
30
40
50
HIGH
LOW
2nd low
TROUGH
COL
RIDGE
1000 +/WIND
Pressure Areas
• Lows move at about 500 miles a day in the
summer and faster, about 700 miles a day,
in the winter.
• Flying from
a HI to a LO
“LOOK
OUT
BELOW”
H
L
– LAPSE RATES
– RADIATION
– TEMPERATURE
–
TURBULENCE
–
AIR MASSES
–
FRONTS
–
WATER DROPLETS
LAPSE
RATES
LAPSE RATES
•
•
•
•
•
•
•
•
•
STANDARD LAPSE RATE
1.98OC
DRY ADIABATIC LAPSE RATE
3OC
SATURATED ADIABATIC LAPSE RATE
1.5OC
SATURATED RANGE ACTUALLY 1.1OC TO 2.8OC
STEEP LAPSE RATE
SHALLOW LAPSE
CONDITIONALLY UNSTABLE – AIR DRY – STABLE
CONDITIONALLY UNSTABLE – AIR WET - UNSTABLE
POTENTIAL INSTABILITY – AIR MASS ASCENT
SHORT
RADIATED AS
LONG WAVE
Pg 2-5
Radiation Absorption & Windows
Pg 2-4
Radio Horizon
Radio transmissions less than about 10 metres wavelength (VHF,
UHF, RADAR) are refracted downward by the atmosphere, roughly a third
beyond the distance to the visual horizon.
A strong inversion and a significant humidity decrease with height
can cause greater refraction. Such a layer is called a radio duct. It is
typically 50 to 1,000 feet deep. The bend in the path is just enough for the
wave to curve back to the surface, bounce off the earth, and continue on
several further bounces. This is known as anomalous propagation. It is
not related to the Ionosphere and its influence on radio waves.
Page 4-10 Air Command Weather Manual
SUN’S PARTICLES and
UV RADIATION
THERMOSPHERE
MESOPAUSE
- 108
IONOSPHERE
O2 H2 N2 fluoresce
275000 feet
MESOSPHERE
STRATOPAUSE
- 2.5
165000 OZONOSPHERE ABSORBS UV
STRATOSPHERE
65000 HENCE TEMP INCREASE HERE
DEEP OVER POLES
MAY BE THIN OVER EQUATOR
33000
O3 CORROSIVE & HARMFUL
- 56.5
SEA LEVEL
SEASONAL
HEATING
HEAT & IT’S MOVEMENT
• The atmosphere is heated from below.
• Temperature increase decreases density.
• Advection: horizontal movement of air. Cold air
becomes warmed by the ground as it moves over it
• Convection: sun heats ground, ground heats the air
• Turbulence: vertical mixing of air due to winds and
convection
• Compression: air sinks, compresses and heats
(Chinooks, highs)
AIR IS A HUGE
TRANSPORTER
OF HEAT BY
VIRTUE OF THE
MOISTURE
EVAPORATED IN
IT AS WATER
VAPOUR.
HEATING the TROPOSPHERE
Advection: horizontal movement of air.
Cold air becomes warmed (infrared) by
the ground as it moves over it
CHANGES OF STATE
Convection: sun (short
wave) heats ground,
ground (longer wave)
heats the air
Turbulence:
vertical mixing of air
due to winds and
convection
MECHANICAL TURBULENCE
TURBULENCE
• Mechanical: Friction between the air and ground
causes eddies. Instability in the air aids in turbulence.
• Thermal: Convection currents such as those found in
storm clouds can be great enough to cause structural
failure to some aircraft.
• Frontal: Two opposing air masses produce turbulence
in the frontal zone.
• Wind shear: Any marked changes in wind with
height produces local areas of turbulence.
• CAT: Clear air turbulence (Jet streams)
CLOUD CLASSIFICATION
• Turbulence related – stable or unstable
• Rain - showers vs. steady
• Four families of cloud as below
LOW CLOUD
3,000 ASL
MIDDLE CLOUD
7,000 ASL
MIDDLE CLOUD
11,000 ASL
HIGH CLOUD
30,000 ASL
Turbulence Levels
• Light: slight changes in attitude, slight
strain on seat belts.
• Moderate: more intense, definite strain
• Severe: large abrupt changes in altitude,
attitude and airspeed. Occupants forced
violently against seatbelts.
Mountain Waves
L
C
L
R
Rapid pressure
drop associated
over crest of hill
Cap clouds, Rotor clouds
and Lenticular Clouds
Air Masses
• An air mass is a large section of the
troposphere with uniform temperature
and moisture in the horizontal.
• Weather in an air mass is determined by:
– moisture content
– cooling process
– stability
• Formed over water: Maritime
• Formed over land: Continental
Air Mass Stability
• Weather in an air mass is determined by:
– moisture content – saturated or unsaturated
adiabatic lapse rate if cooled?
– cooling process – various lift types
– stability
• Cold air mass – usually unstable
• Warm air mass – usually stable
Air Masses of North America
• Continental Arctic: Ca
– not in summer; low water content; warmed from below, strong winds produce turbulence;
heap clouds and snow showers; rarely in B.C. except as a cold-air invasion
• (Continental Polar: Cp)
• Maritime Arctic: Ma
– starts as Ca that spends some time over the northern Pacific ocean; moist and unstable
at high altitudes; stratocumulus and cumulus; pe/sn/-shra; Summer: northern lakes affect
air mass
• Maritime Polar: Mp
– more time spent over Pacific ocean; warmer in lower levels; more stable than Ma;
orographic lifting makes rain west of mountains and dry east of mountains; Summer:
Tsra/Cb
• Maritime Tropical: Mt
– very warm and moist; Gulf of Mexico, Caribbean & south of 30°N; Winter: rarely at
surface N of Great lakes, but present at high altitudes; unstable when Frontal lift;
sn/ra/zr/icing and turbulence; FOG (east coast); Summer: shra/tsra
POLAR
FRONT
Fronts
• The transition zone between two air
masses is called a front.
• Named by the movement of the cold air:
– Cold Front: that portion of the front where
the cold air is advancing
– Warm Front: that portion of the front where
the cold air is retreating
– Stationary Front: the cold air is neither
advancing nor retreating.
– Occluded Fronts and Trowals: trough of
warm air aloft.
The Cold Front
• Factors:
•
•
•
•
•
•
• Moisture of the warm air mass
• stability of the warm air mass
• speed and steepness of the frontal surface
Wind: Veer, some gusts
Temperature: drops
Visibility: improves after passage
Pressure: approaching front, pressure will drop, then
rise after passage
Turbulence: usually associated with Cb’s
Precipitation: showery in character, usually a narrow
band 50 n.m.
Cold
Warm
Cold Front
Cold Front
The Warm Front
• Factors:
•
•
•
•
•
•
•
•
• Moisture Degree of overrunning
Wind: Veer
Frontal Slope: 1 in 150 to 1 in 200
Temperature: gradual rise
Visibility: low ceiling and low visibility; fog
Pressure: drop, then rise
Turbulence: usually little
Precipitation: steady precipitation
CI, CS, AS, NS
Warm
Stability
Cold
The Warm Front
WIND SHEAR @ WARM FRONT
FRONTAL WAVE
FRONTS
FRONTS
Warm
Colder
Cold
Warm
Colder
Cold
Warm
OCCLUSION or Occluded Front
Colder
Cold
Precipitation
• Precipitation occurs when water droplets
grow sufficiently in size and weight and
then fall due to gravity.
– Showery precipitation: Cumulus
– Steady precipitation:
Stratus
• Condensation Nuclei
– Smoke, sea salt, etc.
Precipitation
.
Precipitation
MOISTURE CONTENT
@40OC
one cubic metre of air can
hold 50 grams of water vapour. One
M3 of air weighs about 1.35 kg. This
represents about 3.5% by weight.
+