Transcript Aviation Meteorology

Lesson 01
Atmospheric Structure

Composition, Extent & Vertical Division
Composition

By Volume
Nitrogen
(N2) 78%
Oxygen (O2) 21%
Others (1%)
 Carbon
Dioxide (CO2) 0.035%
 Ozone + Others(Neon, Xenon etc)
Water
Vapour (variable from 0 - 4% locally)
Composition con’t



Analysis reveals no variation in its composition
up to at least 60km
except for increasing concentrations of Ozone
in the upper Stratosphere.
At higher altitudes, the force of gravity being
less causes the proportions to change.
Composition con’t


None of these gases changes its state within the
normal temperature range of the atmosphere so dry
air remains invisible.
Only water vapour changes its state
 water
 gas  solid
The water cycle, illustrating evaporation,
condensation & precipitation
5
The 3 M’s:-

Moisture
 Mass
 Movement
6
Properties of the Earth’s Atmosphere

The earth’s atmosphere varies both vertically and
horizontally in terms of:
- Pressure
- Temperature
- Density
- Humidity
Properties of the Earth’s Atmosphere, contd.

The atmosphere is also a poor conductor of heat and
being a gas is extremely fluid and only supports life in
the lower levels.
Fifty percent of the
atmosphere is below the
500mb pressure level
(about 18,000 feet).
Vertical Division



The atmosphere extends to about 1000 km
above the earth’s surface and
consists of several layers, each with its own
properties.
The layers are defined by the temperature
profile as shown in the following diagram..
Vertical Division
Ionosphere
11
Troposphere








Layer in contact with surface
Contains 80% of atmosphere
Temperature decreases with height
Until Tropopause reached
Zone of vertical mixing by convection and
turbulence
Contains most of water vapour
Zone of clouds and weather
Heated from below
Tropopause

Indicated by marked change in lapse rate

Upper limit of cloud and weather




Lowest tropospheric temperatures at this
level
Strongest winds aloft just below it
Height varies according to season and
latitude
H2O decreases, O3 increases
Typical Average
Tropopause Heights and
Temperatures
Tropopause
Height
Tropopause
Temperature
Equator
56 000 ft
-75C
Latitude 50N
37 000 ft
-55C
Poles
27 000 ft
-45C
Variation in Height of Tropopause






The thickness of the Troposphere will vary
according to temperature.
Lower when the air is cold (i.e. polar latitudes)
Higher when air is warm (i.e. equatorial latitudes)
Height therefore depends on season and latitude
Coldest tropopause temperatures over the equator
Breaks in tropopause caused by jet streams
Variation of Surface Pressure with
Height of Tropopause

High tropopause
 high
air column
 high surface pressure
 more prevalent in summer
 near equator

Low tropopause
 low
air column
 low surface pressure
 more prevalent in winter
 near polar latitudes
JA, JB, JC =
Jetstreams
Height/temperature graph for tropopause
17
Layered structure defined by the temperature profile (ELR) through the
atmosphere.
(Radio sounding)
Radio Sonde
19
Stratosphere




Temperature increases with height to
about 50 km.
Contains warm Ozone region in upper
levels at 40-50 km.
Weather does not penetrate but some
severe CB’s may penetrate several 1000’s
of feet.
Nacreous clouds form at about 20-30 km
Nacreous Clouds
Stratopause


Marks upper limit (50 km), of
the stratosphere.
Maximum temperature just
below freezing.
Mesosphere



Region of decreasing temperature
Noctilucent clouds form at
approximately 80 - 85 km.
Usually visible in summer in
Northern sky near midnight.
Noctilucent Cloud
North Ayrshire Scotland
1988 July 02-03 00005 UTC
Mesopause



Marks the upper limit of the
Mesosphere.
Height approximately 80-90 km.
Temperatures between -120°C
(summer) & -50°C (winter) at high
latitudes
Thermosphere



Zone of increasing temperature
Upper limit undefined.
Merges into the
Exosphere/Ionosphere.
Ozone in the
Stratosphere



90% of Ozone found
here.
Absorbs harmful Ultra
Violet (UV) radiation.
UV Radiation
causes skin cancers.
 destroys DNA
molecules.


Ozone filters in
aircraft



Strongly absorbs IR
earth radiation
Absorbed energy reradiated back to earth
Helps maintain the
thermal balance in the
atmosphere
Ozone Production


Ozone produced by interaction of
molecular O2 and UV radiation
 O2
+ UV  O + O
 O2
+ O  O3
Ozone forms mainly above 25 km
but drifts down producing a peak
concentration at 25 km.
Ozone Destruction


Ozone is also destroyed by UV
radiation.
 O3
+ UV  O2 + O
 O3
+ O  2O2
Ozone is also destroyed by the
collision between two ozone
molecules.
 O3
+ O3  3O2
Ozone Balance



Ozone between 25 and 35 km is maintained
by a delicate natural balance
Ozone can be reduced by natural events e.g.
solar flares and cosmic rays.
Pollutants such as fluorocarbons also destroy
ozone.