Subtropical anticyclones

• What is the main topic of today's lesson?

  Climate and weather with specific reference to subtropical anti-cyclones and resultant weather over South Africa
• What is an anticyclone?

  An anticyclone is a high pressure cell.
• What are the three subtropical anticyclones affecting Southern Africa?

  • South Atlantic High Pressure System
  • South Indian High Pressure System
  • Kalahari Continental High Pressure System
• How do subtropical anticyclones influence weather in South Africa?

  They play an important part in determining weather conditions for summer and winter.
• What is the role of synoptic weather maps in this lesson?

  To interpret the influence of high pressure systems on weather.
• What is the effect of the cold Benguela current on the South Atlantic High Pressure System?

  It strengthens the high pressure system due to more subsiding air.
• Why is the Kalahari High Pressure Cell less strong than the South Atlantic High Pressure System?

  Because it is situated over land and not over oceans.
• What happens to air in the South Atlantic High Pressure System?

  Descending air heats up and creates a permanent inversion.
• How does the South Indian High Pressure System affect weather in summer?

  It brings warm moist air that can cause precipitation.
• What is the Kalahari High Pressure Cell's behavior in winter?

  It is stronger in winter due to colder temperatures and more subsiding air.
• What is the impact of the Kalahari High Pressure Cell in summer?

  It is weaker in summer due to less subsiding air.
• What are the seasonal effects of the Intertropical Convergence Zone (ITCZ) on high pressure systems?

  • In winter, the ITCZ is in the northern hemisphere, affecting high pressure systems.
  • In summer, the ITCZ moves to the southern hemisphere, altering the movement of high pressure cells.
• How do high pressure cells affect cold fronts in winter?

  They bring in frontal rainfall over the western cape and colder conditions.
• What happens to the weather patterns when high pressure cells move southward in summer?

  They block cold fronts from entering, resulting in warmer conditions.
• What is an inversion layer?


  An inversion layer occurs when warmer air is above cooler air, preventing moisture from rising.
• How does the Kalahari High Pressure System affect rainfall in winter?

  It leads to less moisture and very little rainfall over the interior.
• What happens to temperature range during winter under the Kalahari High Pressure System?

  The temperature range will be higher due to dry conditions.
• What changes occur in summer regarding the inversion layer and moisture in the Kalahari region?

  The inversion layer rises, allowing moist air to bring rainfall.
• What are line thunderstorms and how do they form?

  • Line thunderstorms develop along a moisture front.
  • They occur when cold dry air from the southwest meets warm moist air from the northeast.
  • Rapid uplift of warm air leads to cumulonimbus clouds and thunderstorms.
• What is the role of the moisture front in thunderstorms?

  The moisture front separates cold dry air from warm moist air, leading to uplift and storm formation.
• How does the coastal low pressure system affect weather on either side of the pressure cell?

  It causes different weather conditions due to onshore and offshore currents.
• What direction does air circulate in a coastal low pressure system in the Southern Hemisphere?

  Clockwise
• What is the effect of onshore currents compared to offshore currents?

  Onshore currents bring moisture, while offshore currents are dry.
• What are the differences in weather conditions caused by a coastal low pressure system?

  • Onshore current: Brings moisture and affects weather with precipitation.
  • Offshore current: Causes dry conditions and less precipitation.
• What direction do low pressure systems flow in the southern hemisphere?

  Clockwise
• What are the weather conditions on either side of a low pressure cell in the southern hemisphere?

  • Onshore current: brings moisture, leading to moist and cloudy conditions.
  • Offshore current: brings dry air, leading to warmer and drier conditions.
• What happens to air when it moves from land to sea in a low pressure system?

  It causes warmer, drier conditions with offshore winds.
• What occurs when air moves from sea to land in a low pressure system?

  It leads to moist, cloudy conditions and potential rainfall.
• What is the Kalahari high pressure cell associated with?

  It is associated with winter weather conditions.
• What are the necessary conditions for berg winds to occur?

  • A well-developed Kalahari high pressure cell.
  • A coastal low pressure cell.
  • Occurs during winter.
• How does air flow from the Kalahari high pressure cell to the coastal low pressure cell?

  The air subsides from the plateau down the escarpment.
• What is the dry adiabatic temperature lapse rate?


  It is $1 \text{°C for every } 100 \text{ meters}$.
• Why does the air become drier and hotter as it moves down the escarpment?

  Because moisture evaporates from the air as it heats up.
• What type of wind is created by air moving from land to sea in this context?

  It is an offshore wind.
• What can berg winds lead to in terms of fire risk?

  They can cause wildfires due to dry conditions.
• What happens when a cold front comes in contact with a coastal low pressure system?

  It can drop the temperature and bring cooler conditions.
• What are the general winter conditions associated with anticyclones?

  • Anticyclones are in a northerly position.
  • Allow cold fronts to affect the country.
  • Bring frontal rainfall over the western cape.
  • Associated with dry conditions and clear skies over the interior.
• How do summer conditions differ from winter conditions regarding anticyclones?

  In summer, anticyclones generally prevent cold fronts from affecting the country.
• What are the characteristics of light thunderstorms in summer conditions?

  • Associated with higher temperatures and humidity.
  • Can lead to rainfall over the interior.
  • Less frequent in the western cape due to frontal rainfalls.
• What do weather symbols represent in meteorology?

  • Rain, drizzle, showers, snow.
  • Cloud cover (clear sky, octas).
  • Wind speeds and direction.