This note pack is a complete summary with diagrams. It summarises all the content for Topic 2 : Climate and Weather Introduction. Chapter 1 : Mid-Latitude Cyclones in the Focus Geography Grade 12 Learner's Book.
Terminology
Converging - coming together
Coriolis Force - force that causes deflection of moving objects due to rotation of Earth on its axis;
greatest at poles, least at equator
Deflects - turn away or cause something to turn away; swerve
Mid-Latitude Cyclone - low-pressure cell develops in mid-latitudes & travels from west to east
Pressure Belts - bands of high / low pressure surround Earth at certain latitudes, eg. equatorial
low-pressure at equator
Air Mass - huge mass of air, extending hundred kilometres, similar temperature & humidity
Jet Stream - band of very strong westerly winds high in atmosphere - above 9 000m - partly controls
development of mid-latitude cyclones
Polar Front - zone where cold polar air mass & warm tropical air mass meet
Cold Front - border zone between cold air mass & warm air mass. Winds cold sector blow against cold
front
Cold Sector - area on the ground affected by cold air in mid-latitude cyclone
Warm Front - border zone between warm are mass & cold air mass. Winds in the warm sector blow
against the warm front
Warm Sector - area on the ground affected by warm air in mid-latitude cyclone
Backing - change direction of winds in anticlockwise direction
Cold front occlusion - occlusion overtaking cold air is colder than cold air ahead of it
Cross-section - side view explain what you would see. Example of weather experienced at MLC
Isobaric diagram - view from top you see on synoptic weather map
Occlusion - late stage development of mid-latitude cyclone
Where cold front to rear catches up with leading warm front, lifts warm air off ground & meet cold air
ahead of warm front
Veering - change direction of winds in clockwise direction
Warm front occlusion - occlusion where overtaking cold air is warmer than cold air ahead of it
General Characteristics
● Low-pressure cell develops in mid-latitudes & travels from west to east
● Bring cold, windy & wet weather
● Caused pressure & wind patterns of mid-latitude cyclones & air masses involved
● Known as Frontal depressions, Temperate Cyclones, Temperate Depressions & Extra-Tropical
Cyclones
● Due to pressure, wind patterns & air masses involved in formation
, Effects of Pressure & Wind Patterns on Mid-Latitude Cyclones
● Low Pressure Cell
● Isobar pattern & winds converge in mid-latitude cyclone in southern hemisphere
● Pressure is low at centre & increases outwards
● Winds blow around and into low-pressure cell clockwise direction
● Winds don;t blow straight along pressure gradient but are deflected by Coriolis Force
● Winds still converge into low-pressure cell but due to Coriolis Force, circulation is anticlockwise
Effect of Air Masses on Mid-Latitude Cyclones
● Develop in middle latitudes, between 30° & 60° north & south of equator
● Where cold polar air mass meets warm subtropical air mass in zone called Polar Front
● When air masses meet, warm subtropical air rises & cold polar air wedges in underneath
● As it rises, warm air cools & condensation of water vapour occurs
● Produces clouds & rain main weather characteristics of mid-latitude cyclones
● Cover large area between 1 500 & 3 00 km in diameter
● Move 1 200 km in a day
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