Download GLOBAL ATMOSPHERIC CIRCULATION

GLOBAL ATMOSPHERIC
CIRCULATION
• GLOBAL ATMOSPHERIC CIRCULATION
• AIR MASSES
• FRONTS
• PRESSURE SYSTEMS
Simple Model of
Global
Circulation
Ideal Global Circulation
Initially, assumes that the
Earth:
• Has a uniform surface
• It is not rotating
• It is not tilted.
Approximate actual global circulation on
the Earth
Actual global circulation
is affected by
- Rotation of the Earth
- The Earth’s Tilt
- The irregular
surface of the land
- The deference in
land and sea
surfaces
Air masses
Huge bodies of air within the troposphere
characterized with uniform weather
conditions and characteristics are called Air
masses.
Regions of air masses origin are known as
source regions.
Ideal source regions are:
• Large continental areas
• Major bodies of water.
Air mass clasification
Typically, air masses are classified according to the
characteristics of their source of origin or area of
formation. According this classification AM can be
equatorial, tropical, polar or arctic. Air masses
are also classified as continental or maritime in
terms of moisture characteristics.
The combination of these two characteristics give the
common classification of AM
maritime polar (mP)
continental polar (cP)
maritime tropical (mT)
continental tropical (cT)
Maritime arctic (mA)
continental arctic (cA)
Arctic AAM Originates in the polar ice cap in
the winter. Antarctic is used for the Southern
Hemisphere
Polar PAM Originates between 40° and 60 °
latitude, in the summer up to 80 °latitude
Tropical TAM Originates in the subtropical
high pressure cells. In summer tropical
regions can also form over the large
continents.
Equatorial EAM Forms in the region between
the subtropical highs on both sides the inter
tropical convergence zone.
Thermodynamical classification of AM
According thermodynamical properties AM can be
classified as:
- Cold AM (It is colder then underlying surface)
- Warm AM (It is colder then underlying surface)
- Stable AM (No conditions for convection)
- Unstable AM (There are conditions for convection)
- Neutral AM (do not change its properties significantly
when travelling from the source region)
As an air mass is moving from the source
region, it is modified or change its properties.
Weather and flight conditions
Unstable and moist
• CU,CB, TS
• Moderate to heavy showers of rain, hail
• Moderate to sever icing and turbulence in
cloud
• Visibility good outside cloud
• Strong squalls and gusts
Unstable and dry
Cu (2-4 octas)
Weather and flight conditions
Stable and moist
• St, Sc
• Drizzle presipitation
• Light to Moderate icing and light turbulence
in cloud and presipitation
• Poor visibility due to Fog, mist and
precipitation
• ice-covered ground
Stable and dry
No clouds, poor visibility due to dust, smoke,
haze , low drifting, blowing (Snow,Dust,Sand)