Mid latitude cyclones

• mid latitude cyclones are also known as extra tropical cyclones, frontal depression and temperate cyclones
• General characteristics of mid latitude cyclones

  1. move from west to east
  2. driven by westerly winds
  3. found between 30-60 N/S
  4. affects south Africa during the winter season
  5. presence of both the warm front and cold front
• low temperatures are associated with high pressure where the is the divergence of air as air moves from high pressure to low pressure

  high temperatures are associated with low pressure and convergence of air
• front where cold air and warm air meet is called polar front found at the 60 line of latitude N/S
• warm front has a gentle gradient
• cold front has a steep gradient which results in the rapid rising of warm air to form tall cumulonimbus clouds
• clouds that from on the warm front are called nimbostratus clouds
• mid latitude cyclone affect the western cape in winter because during the winter sun the heat equator will be further north as the sun is directly above the tropic of cancer making pressure belts to move northwards
• areas of formation of mid latitude cyclones is that they form between 30 and 60 line of latitude N/S
• conditions necessary for the formation of mid latitude cyclones

  • presence of both warm front and cold front
  • frictional drag caused by the difference in temperature and speed of the two air masses
  • warm front and cold front move in opposite direction, as the cold front is dense and faster it will undercut the warm front forcing the warm air to be uplifted
• 4 stages of development

  1. initial stage
  2. wave formation
  3. mature stage
  4. occlusion stage
• initial stage

  • warm subtropical air meets with the cold polar air at the polar front
• wave formation

  • frictional drag occurs
  • warm air becomes uplifted as the cold dense air undercuts the warm air forcing the warm air to raise
• mature stage

  • wave deepens
  • warm sector and cold sector fully develop
  • warm air moves up the steep gradient of the cold front to form towering cumulonimbus clouds which are associated with heavy rainfall
  • warm air moves up the gentle gradient of the warm front to form nimbostratus clouds which are associated with light rain
• occlusion stage

  • cold front catches up with the warm front as it is dense and faster. warm air is uplifted from the surface and cold air is left from the surface. temperatures decreases and pressure increases
• weather associated with mid latitude cyclones

  1. cold front conditions->temperature drops, pressure increases, humidity increases, wind speed increases, cloud cover increases and associated with heavy rainfall
  2. warm front conditions-> temperature increases, pressure decreases, humidity decreases, wind speed decreases, cloud cover decreases and associated with light rainfall
  3. occlusion depends, if it is a warm occlusion give out the characteristics of the warm front conditions
• Social impacts of natural disasters:

  • Injuries and fatalities
  • Destruction of houses
  • Homelessness and lack of shelter
  • Spread of diseases like waterborne diseases due to polluted water from siltation in dams and destroyed fresh water sources by flooding
• Economic impacts of natural disasters:

  • Soil erosion leading to reduced production in industries
  • Job losses due to the inability to plant crops in eroded soil
  • Increased water availability for agriculture from filled dams leading to higher industrial production
  • Pest control due to low temperatures leading to increased crop production
• Environmental impacts of natural disasters:

  • Destruction of habitats
  • Extinction of animals
  • Soil erosion
  • Infrastructure damage (roads, bridges, buildings)
  • Crop destruction
  • Filling up of dams
• management strategies we can implement

  • build houses on high lying areas
  • evacuate people living in low lying areas to high lying areas
  • update weather systems such as early warning systems that can help people prepare in time for evacuation
  • securing of boats
  • stocking up water, food and medical supplies
  • preparing first aid kits
  • efficient drainage system
  • enclose livestock
• impact of SIHP and SAHP

  • SAHP(south atlantic high pressure)acts as a ridging cell as its isobars extends to the inland area of south africa
  • SIHP(south indian high pressure) acts as a blocking high
  • mid latitude cyclones move from west to east, as it encounters the SAHP it is going to weaken as the mid latitude cyclone should maintain its low pressure for it to function
• on a wave formation diagram, the air underneath is the cold air and the air above is the warm air and the front where they meet is called the polar front
• the oldest mid latitude cyclone is further to the east
• in the southern hemisphere circulation of air is in the clockwise direction and in the northern hemisphere the circulation of air is in the anticlockwise direction