Weather

• Weather


  The atmospheric conditions of a given place over a short period of time
• Elements of weather


  • Temperature
  • Humidity
  • Precipitation
  • Atmospheric pressure
  • Sunshine
  • Cloud cover
  • Wind
• Weather station


  A place set aside for the observing, measuring and recording of various weather elements
• Locations of weather stations


  • Colleges
  • Schools
  • Agricultural institutions
  • Meteorological departments
• Stevenson screen


  • Directs sunlight away
  • Provides shade conditions for accurate temperature readings
  • Allows free air circulation to measure actual air temperature
• The Stevenson screen is made of wood to prevent absorption of heat
• Factors for siting a weather station


  • Open, away from trees and buildings to allow free flow of air
  • Gentle, fairly level land with wide view of the sky
  • Away from paved surfaces to avoid splashing water
  • Properly fenced for security
• Types of records kept in a weather station


  • Daily records
  • Monthly records
  • Graphical record book for annual graphs
• Sunshine


  The direct rays of the sun reaching the earth's surface
• Factors affecting sunshine


  • Cloud cover
  • Aspect (slope facing the sun)
  • Latitude
• Sunshine recorder


  An instrument that measures the duration of sunshine by burning a trace on a card as the sun moves across the sky
• Temperature


  The degree of hotness or coldness of an object or place
• Types of thermometers


  • Minimum thermometer
  • Maximum thermometer
  • Six's thermometer (minimum and maximum)
• Minimum thermometer


  Measures the lowest temperature of the day
• Maximum thermometer


  Measures the highest temperature of the day
• Six's thermometer


  Measures both the minimum and maximum temperature of the day
• Mean daily temperature


  The average daily temperature, calculated by adding the daily maximum and minimum and dividing by 2
• Daily diurnal range of temperature


  The difference between the daily maximum and minimum temperature
• Mean monthly temperature


  The average temperature for the month, calculated by adding the daily mean temperatures and dividing by the number of days
• Mean annual temperature


  The average temperature for the whole year, calculated by adding the mean monthly temperatures and dividing by 12
• Factors influencing temperature


  • Altitude
  • Distance from large water body
  • Aspect
  • Cloud cover
  • Amount of water vapour
  • Latitude
  • Winds
  • Human activities
  • Position of the midday sun
  • Transparency of the atmosphere
• Temperatures are higher near the earth's surface due to terrestrial radiation, greenhouse gases, and the presence of air molecules and living organisms
• Air cools as it rises due to expansion and rarefaction at higher altitudes
• Clear skies at night allow terrestrial radiation to escape, leading to low temperatures
• Greenhouse gases


  Gases such as chlorofluorocarbons that trap heat in the atmosphere and increase temperatures
• Thick cloud cover at night


  • Traps heat into the atmosphere below, bringing warmer nights
• Humidity


  Amount of water vapour in the atmosphere
• Humid air


  • Absorbs heat during the day and retains it at night, increasing temperature
• Latitude


  Distance from the equator
• Increase in latitude

  Decrease in temperature
• Equator


  Receives high temperatures due to shorter distance and 90 degree angle of sun's rays
• Polar regions


  Receive low temperatures due to longer distance and acute angle of sun's rays
• Tropic of Cancer


  When the sun is overhead, the Northern hemisphere receives longer daylight hours and more heat
• Inter-tropical convergence zone (ITCZ)


  Area within the tropics where temperatures are highest when the midday sun is overhead at the equator
• Cold ocean currents


  • Bring a cooling effect on adjacent lands, lowering temperatures
• Warm ocean currents


  • Bring a warming effect on adjacent lands, increasing temperatures
• Warm winds


  • Bring a warming effect, increasing temperatures
• Cold winds


  • Bring a cooling effect, lowering temperatures
• Vegetation


  • Creates shade which lowers temperatures
• Industrial activities produce greenhouse gases that increase temperatures