MeteorologyMeteorologySubject: ADVANCED AERONAUTICS Subject Code: AER 200Faculty: Brian CARLICK Date: January 11, 2006
– COMPOSITION AND STRUCTURE OF THE ATMOSPHERE– PRESSURE– STANDARD ATMOSPHERE– TEMPERATURE– MOISTURE– STABILITY– WINDS– CLOUDS
Atmosphere CompositionAtmosphere Compositionand Propertiesand Properties
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
atmospheric pressure– Water vapour usually less
than 1% but can be 3.5% 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Oxygen 21%
Water/Other 1%
Nitrogen 78%
Properties / Properties / Structure of the Structure of the
AtmosphereAtmosphere
• Water Vapor is essential for weather– found in lower levels– responsible for clouds and precipitation
• H2O vapour (10) is lighter than O2 (16) or N2 (14)
• H2O content varies hour to hour, day to day, by season and by latitude
• Water content changes depending on temp & pressure
Properties / Properties / Structure of the Structure of the
AtmosphereAtmosphere
• Air is a fluid
• Mobility, expansion & compression
• Lifting agents can be Frontal, Thermal, Orographic, Mechanical
• Rising air is subjected to reducing pressure and expands and cools
As air compresses (sinks) pressure
increases andtemperature
increases
As air expands (rising) pressure decreases and temperature decreases
25 oC
20 oC
15 oC
TROPOSPHERE
TROPOPAUSE
STRATOSPHERESTRATOPAUSE
MESOSPHERE
MESOPAUSE
THERMOSPHERE 3000 ° C @700km
IONOSPHERE
Vertical StructureVertical Structure
SEA LEVEL
Vertical StructureVertical Structure
-110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 500
10
20
30
40
50
60
70
80
90
100
110
120
275,000 feet
36,089 feet-56.5 °C
-2.5 °C
-108 °C
KM
165,000 feet
Temperature distribution
-108 °C
-56.5 °C
-2.5 °C
EXOSPHERE
Starts 500 to 800 km up
6 to 30 miles
MESOPAUSE
STRATOPAUSE
TROPOPAUSE
IONOSPHERE
80km to 400km
°C
Humidity and Dew pointHumidity and Dew point
• Warm air can hold more moisture.• The water vapor a volume of air can hold is governed
by its temperature.• Air is said to be saturated when it contains the
maximum amount of water it can hold at that temperature.
• Dew point - the temperature to which unsaturated air must be cooled to become saturated.
• Relative Humidity - the ratio of actual water vapor present in the air to the amount which that volume of air would hold if saturated.
• When air is heated, without adding water, the relative humidity decreases.
• The Thermosphere is important because it contains properties of mobility, and it has a capacity for expansion and contraction.– Allows movement under it, ie. lows and highs
• The Thermosphere also contains the Ionosphere, which can affect radio waves.
– Jet Streams are found at the top of the troposphere, much lower than the thermosphere. They are higher at the equator and lower at the poles. They descend in winter and rise in summer.
• Is important for determining altitude
• Distribution determines winds (mobility).
• Is Force exerted by the air at that altitude Area
• Station pressure: is the actual atmospheric pressure at the elevation of the observing station.
• MSL: is used to compare the pressures of stations with different elevations.
Pressure:
Pressure, Pressure, Density & & Altimeter settings Altimeter settings
500 feet1000 feet
Sea level29.9229.92
29.4229.92
28.9229.92
18000 feet
34000 feet 7.4029.92
14.9029.92
14.9029.92
Eg. Actual pressure Pressure setting
Defining the Standard AtmosphereDefining the Standard Atmosphere
• 29.92”Hg (1013.2 mb) @ sea level
• 15° C @ sea level
• 1.98° C per 1,000 feet
• 1”Hg = 1,000 feet (varies with height)
• 1 mb = 30 feet
• Air is presumed perfectly dry for standard
Low PressureLow Pressure• Low or Cyclone is rising air• Bad weather, poor visibility • Stratus clouds, light winds • Movement:
– Summer: 500 miles / day– Winter: 700 miles / day
• Winds:– Above 3000agl: parallel to isobars– Below 3000agl: INTO the low
• Consistent day and night temperatures• Low pressure is by comparison to surrounding areas• Counterclockwise rotation in Northern hemisphere
Buys Ballot’s LawBuys Ballot’s Law
• Stand with the wind at your back.
• Stick out your left arm.
• Your fingers will point to the center of the low pressure area !!!
High PressureHigh Pressure
• Anti-cyclone is descending air, compression occurs• Clockwise circulation in Northern hemisphere• Highs fill in Lows• Surface winds blow outwards in a slow spiral• Clear skies predominate• Higher day temperatures, lower night temperatures• Good visibility• Cumulus type clouds• Breezy
WindWind• The heating of the earth’s surface is
responsible for circulation. The sun heats the earth which then radiates the heat, heating the adjacent air at the surface.
• Upper winds flow parallel to isobars, with
wind speed determined by the spacing.• Surface winds are slower due to surface
friction, and will blow in or out depending on the surrounding pressure.
Gusts and SquallsGusts and Squalls
• Gusts: rapid, irregular fluctuation in velocity and direction. Peak 5 kt higher than 2 minute average
• Squalls: longer in duration. 15 kt higher than mean speed and peak for 2 minutes
• Stable vs. Unstable (Horizontal/Vertical)
• 2 main types - Stratus vs. Cumulus
• Heights of clouds give 4 families
- High
- Middle
- Low
- Vertical development
Clouds
GROUP TOPS 40,000
HIGH
CLOUDS
BASE 20,000
TOPS 20,000
MIDDLE
CLOUDS
BASE 6,500
TOPS 6,500
LOW
CLOUDS
BASE SURFACE
CLOUDS OF
VERTICAL
DEVELOPMENT
BASE 1,600 UP
TYPE CIRRUS
CI
CIRROSTRATUS
CS
CIRROCUMULUS
CC
ALTOSTRATUS
AS
ALTOCUMULUS
AC
ALTOCUMULUS CASTELLANUS
ACC
STRATUS
ST
NIMBO STRATUS
NS
STRATOCUMULUS
SC
STRATUS FRACTUS
SF
CUMULUS FRACTUS
CF
CUMULUS
CU
TOWERING CUMULUS
TCU
CUMULONIMBUS
CB
CLOUD CLASSIFICATIONSCLOUD CLASSIFICATIONS