Climate and weather Flashcards
What are mid-latitude cyclones?
A low pressure cell which develops in the mid-latitudes and travels from west to east.
Converging winds, into the cell, clockwise
What is Coriolis Force?
Force that causes the deflection of moving objects due to the rotation of the earth on its axis; greatest at the poles and least at the equator.
Mid-latitude cyclones in SA
Where, effects
- develop between 35 degrees S and 70 degrees S (at the polar front)
- southwestern Cape receives winter rainfall = week of cold, cloudy, wet weather
Stages of Development of a mid-latitude cyclone
- Initial Stage
- Mature Stage
- Partially Occluded and Occluded Stage
- Degeneration Stage
Initial Stage (MLC)
- bend in polar front
- LP begins to form and winds deflect
- features: winds strengthen and clouds appear
Mature Stage (MLC)
- cold and warm front form and divide into a warm sector and a cold sector.
- features: affected by cold sector (on ground) - strong winds, overcast skies and rain.
Partially Occluded and Occluded Stage (MLC)
- air is lighter in the warm sector
- cold front overtakes warm front = cold air on ground
- features: cold, nimbus clouds and light rain
Degeneration Stage (MLC)
- LP cell disappears and isobars even out
Features: cold, clouds and rain disappearing
Cold front conditions
- temperature decreases
- pressure decreases (approaching) and increases (arrives)
- humidity decreases
- winds backing
Warm front conditions
- temperature increases
- pressure decreases
- humidity increases
What are tropical cyclones?
A low pressure cell that develops over warm oceans between the tropics
Characteristics of a tropical cyclone
- violent weather conditions
- strong winds
- huge waves
- heavy rainfall
Names of Tropical Cyclones
The first letter of the name tells us how many cyclones have occurred that year.
Where do Tropical Cyclones form?
- 30 degrees N and 30 degrees S
- not between 5 degrees N and 5 degrees S as they depend on Coriolis Force
- occur on the east side of continents with warm ocean currents
What factors are necessary for the formation of tropical cyclones?
- Hot, humid, unstable air = occur in February to April
- intense LP cell
- Coriolis Force (clockwise)
Stages of development of a tropical cyclone
- Formative stage
- Immature stage
- Mature stage
- Degenerating stage
What are the weather condition experienced as a tropical cyclone passes?
- in the eye = hot, humid, calm weather (caused by descending warm air)
- eyeballs = dramatic weather - rapid uplift of air, temperature falls to dew point, heavy rain and thunderstorms
Short term effects on tropical cyclones
- strong winds and flooding = destroy infrastructure
- infected water = spread of disease (cholera)
- power/water supply may be cut off
- flooding = loss of crops and livestock
Long term effects of a tropical cyclone
- contaminated water supplies (sewerage)
- large-scale soil erosion - floods remove valuable topsoil
Strategies that hop to prepare for and manage the effects of Tropical Cyclones
- prediction and warning
- preparing the community (educate on evac routes)
- land use planning
- managing the loss
General characteristics of high pressure cells
- descending, dry, warming air = clear skies and sunshine
- air blows out and anti-clockwise
What HP cells affect South Africa
SAA - South Atlantic Anticyclone
SIA - South Indian Anticyclone
KH - Kalahari High Pressure
Why is the southeaster called “the Cape Doctor”
The strong southeasterly winds blow away the polluted air and has a cooling effect (over the Cape Peninsula and southern Cape)
What is a coastal low pressure system?
- moves from west to east around the coast
- autumn and winter
- onshore flow (behind) = clouds and fog
- offshore flow (ahead) = clear, warm weather
= fire hazard
Why is the city warmer than the surrounding rural areas?
URBAN
- built out of artificial substances - absorb more heat
- artificial sources of heat
- polluted air above them - acting as a blanket
RURAL
- heat lost in evaporation
What is an urban heat island?
When the central part of a city is warmer than the surrounding suburban and rural areas
What is a pollution dome?
A dome-shaped mass of polluted air above a city
What are the causes of pollution domes?
- vehicle exhaust
- burning of fossil fuels
What are the effects of pollution domes?
- health problems (lung infections)
- buildings and trees suffer (sulphur and nitrogen gas mix with rainwater = acid rain)
Strategies to reduce the heat island effect
- change dark surfaces to light reflective surfaces
- ‘greening’ the city (add more parks or water fountains)
