Pressure systems Flashcards
Global circulation cells
Three main cells –
Near equator:
Hadley
Ferrel
Polar
Near poles.
Global circulation cells
Where on the globe are we likely to find the bands of low pressure?
Low pressure areas found at the Equator heat area, and in the region of 60degrees latitude
Global circulation cells
Where on the globe are we likely to find the bands of high pressure?
High pressure areas found at the pole and in the region of 30degrees latitude
Global circulation cells
When you have high level DIVERGENCE, what would pressure would you expect on the surface?
Low pressure found at the surface where high level divergence takes place
Global circulation cells
When you have high level CONVERGENCE, what would pressure would you expect on the surface?
High pressure found at the surface where high level convergence takes place
Low/high pressure areas ?
fronts, secondary depression, trough, thermal low, inland water and geographic
Low pressure areas – fronts, secondary depression, trough, thermal low, inland water and geographic
Low/high pressure areas ?
Ridge, cold and warm highs, blocking high, cold temporary high
Anticyclone (high pressure) areas – high, ridge, cold and warm highs, blocking high, cold temporary high
The central issue in the formation of depressions is ____ _____ __________
high level divergence
Airflow travels which direction around a low in Nth Hemisphere
anti-clockwise
Clockwise in Sth Hemisphere
Ascending air cools leading to cloudy conditions in a high/low pressure?
Depression (low)
A typical front (warm and cold front) occur when a polar depression pushes what into each other?
polar (cold) and tropical (warm) air into each other
Forms within the circulation of the main (primary) depression describes what?
Secondary depression
_________ __________ rotates within the main system in a cyclonic
(clockwise for southern hemisphere, anticlockwise for north hemisphere) direction.
Secondary depression
Troughs of Low Pressure
Can take on two forms (2)
Isobaric trough - extends into other systems
Troughs of Low Pressure
Pressure Systems Aloft: Low
Warm or cold core, where are they likely to be found?
Warm core Low: more likely in tropical depressions
Cold core Low: common for a polar front depression
Cold core will have the top pressure line bulging __
while the warm core will have the top pressure line bulging _____
Cold - down
Hot - up
Thermal lows can occur over relatively warmer _____ in winter.
Thermal lows can occur over relatively warmer seas or lakes in winter.
When cold air over continents move out over a warmer sea in winter
Orographic Low/Depressions (Lee Low)
Substantial wind blowing more or less ______________ to mountain.
Substantial wind blowing more or less at right angles to mountain.
Orographic Low/Depressions (Lee Low)
Windward side: air compressed = localized ____
Windward side: air compressed = localized high
Orographic Low/Depressions (Lee Low)
Lee side: suction effect (convergence) = low pressure
Lee side: suction effect (convergence) = low pressure
Anticyclone (High)
What is Adiabatic warming?
Adiabatic warming occurs in the subsiding air, which generally results in skies becoming cloud free.
Anticyclones (High)
What is the direction of airflow around a high in the northern hemisphere?
Airflow is clockwise in the Northern Hemisphere
Anti-Clockwise in Sth Hemisphere
Anticyclones (High)
What winds would be associated with a high?
Which pressure would be in the centre?
Light winds
Highest pressure is in the centre.
Anticyclones (High)
Hazy conditions may be caused by the ___________ ________
The subsidence inversion may result in hazy conditions
Cold Anticyclones (e.g. Siberia) – Cold Core High
Cold surface temperatures make the lower troposphere cold and dense
Classically found over Siberia in winter.
Pressure levels bulge UP at lower level
Bulge DOWN at high level
Warm Anticyclones (e.g. Azores) – Warm Core High
Excess air in the upper troposphere
Pressure levels bulge UP at both lower and upper levels
Blocking High/Anti-cyclone
Describe: intensity, changeability, examples in summer and winter
The high often becomes very intense
Resulting in consistent weather for a long period of time
Dry & warm in summer
Overcast in winter
