1. no fefinite top
2. aurora measured to 600 miles - satellite drag data extends past 1000 miles
3. despite this, half the weight of the atmosphere is in the lower 18,000 feet
4. in Met, our interest generally extends to around 50,000 feet.
B. Composition
1. (78%) nitrogen
2. (21%) oxygen
3. (0.03%) carbon dioxide
4. (0-4% max) water vapor in varying amounts, depending on the temperature
5. argon
6. dust, pollen, salt crystals, smoke particles, pollusion
note: Of these, water vapor is the most important to meterology.
C. Properties of the Atmosphere
1. Physical Aspects
a) Mobility
- air is fluid with complex motions
- there is a great deal more freedom of motion in the atmosphere than in the sea.
b) Ability to Expand
- expansion causes cooling
- air is often forced to rise, and since the pressure decreases with height, expansion occurs and there is cooling
- this cooling is often sufficient to cause condensation of water vapor and hence cloud and/or precipitation form
- hence clouf and precipitation are common in refions of risinfg air ie. in a LOW (low pressure area)
c) Ability to be compressed
- compression causes warming
- air is often forced to descend, and since oressure increases with depth, compression occurs and there is warming.
- this warming is often sufficient to cause evaporation of water and hence cloud and/or precipitation will dissipate.
- hence clear weather often occurs in subsiding air ie. in a HIGH (high pressure area)
note: the warmer the air, the more moisture that it will hold; the RELATIVE HUMIDITY is the precentage of moisture in the air compared with what the air could hold at that particular temperature; the DEW POINT is the temperature at which the water vopor condenses in a parcel of air
2. Temperature aspects
a) Lapse Rate - rate of change of change of temperature with height
1. positive lapse rate - decrease in temperature with height
2. negative lapse rate - increase in temperature with height
3. zero lapse rate - no change in temperature with height, called isothermal
b) Stability - depent on temperature and moisture
1. stable air - aor parcel returens to point of origin after lift ( no vertical cloud development )
2. unstable air - air parcel rises on its own after initial lift
3. steep or positive lapse rate is unstable
4. inversion or negative lapse rate is stable
5. five types of lift to set off instability
- convection ( heating from below)
- frontal lift
- orographic lift
- mechanical lift
- convergence (aroud a LOW)
6. dry adiabat (dry adiabatic lapse rate (DALR)) - standard rate of cooling with height for dry air is 3 per 100 feet
7. moist adiabat (saturated adiabatic lapse rate (SALR)) - standard rate of cooling with height for saturated air is 1.5 per 1000 feet
8. the dry adiabat is the steeper of the two
9. characteristics od stable and unstable air:
STABLE
-layer clouds -seady precopitation -smooth air -low visibility -fog -inversions or isothermal layers -shallpw lapse rate -resists deplacement
UNSTABLE
-heap type clouds -thouderstorms -showers -turbulence -improved visivility -steep lapse rate -vertical motion develops easily
c) Cooling processes
1. radiational cooling (at night)
2. advectional cooling (day or night)
3. expansional cooling (day or night)
d) Heating processes
1. insolation (day
2. advection heating (day or night)
3. compressional heating or suvsidence (day or night)
3. Atmospheric model (base on temperature - see diagram in WEATHER WAYS)
a) Troposphere
- temperature usually decreases with heifht
- most of the weathe is found here
- top varies between 20,000 and 50,000 feet
- topped by the Tropopause, which is the boundary between the Troposphere and the
b) Stratosphere
- vertical temperature profile is isothermal
- little weather found here (tops of CB's or thunderstorms)
- no vertical motion
- topped by the Stratopause
c) Mesosphere
- marked by increasing then decreasing temperature
- topped by Mesopause
d) Thermosphere
- marked by increasing temperature
Copyright (C) 2006- Project 39., All rights reserved.