CIE Geo - Weather

• Weather


  The condition of Earth's atmosphere at a particular time and place
• Climate


  The average atmospheric conditions in an area over a long period of time (30 years)
• measuring Relative humidity


  - hygrometer, measures water vapour in air

  - 2 bulbs, one wrapped in damp muslin

  - no difference between bulbs = high humidity

  - difference between bulbs = low humidity

  - when air is dry, it evaporates which cools the thermometer

  - when air is wet, no evaporation so reads the same

  - record difference in readings

  - given in %

  
• measuring Temperature


  - Six's thermometer

  - max and min thermometer

  - degrees C

  - when temp rises, alcohol expands, mercury rises on RHS

  - max temp read from bottom of right (metal) index

  - when temp falls, alcohol contracts in opposite direction

  - min temp read from bottom of left index

  
• Mean daily temp calculation

  Max temp + min temp/2
• measuring Rainfall


  - use rain gauge

  - place in open area, 30cm above the ground to avoid splashing and evaporation

  - measured in mm

  - wait 24 hours to read

  - tip into measuring cylinder and read amount

  
• measuring Air pressure


  - barometer

  - measured in millibars

  - small little metal box inside (very little air)

  - as pressure changes, movement on box moves the arrow

  
• measuring Wind direction


  - use a wind vane

  - N,S,E,W

  - place in open location, no obstacle blocking wind (e.g a building)

  - rotation arm shows where the wind is blowing from
• measuring Wind speed


  - anamometer

  - the cups rotate in the wind

  - measured in km/hr

  - place in high, open location to avoid blocking the wind

  - away from trees, buildings (funnelling, slowing down wind)

  
• measuring Sunshine


  - campbell stokes sunshine recorder

  - measures No. of hours of sun per day

  - glass sphere fixed inside a light sensitive chart

  - as the sun moves, it leaves a trace on the chart when shining bright enough (weak sunshine is not recorded)

  
• Stevenson's Screen


  - wooden box where instruments are kept in

  - painted white to reflect the sun

  - louvered sides for air circulation

  - stands 1.2m above ground -> to measure circulating air, not ground radiation

  - thermometer and hygrometer inside (shade temps)

  - placed in open area, on grass (not concrete)

  - in fenced area to avoid tampering from people and animals, and stealing

  
• Factors affecting climate


  - Latitude

  - Distance from the sea

  - Altitude

  - Aspect

  - Prevailing winds

  - Ocean currents
• Factors affecting climate: Latitude

  Its warmer towards the equator as:

  - the Earth is a sphere

  - there's a smaller layer of atmosphere

  - the sun is overhead

  - smaller surface area to heat

  - more concentrated rays
• Factors affecting climate: Distance from the sea

  - Oceans heat up and cool down more slowly than in land

  Summer:

  - Sea in constant motion, takes longer to heat - convection currents

  - Land heats fast as its solid - conduction

  - Coast is cooler that inland in summer

  Winter:

  - land cools quickly

  - Sea retains heat - convection currents

  - Coast is warmer than inland in winter
• Factors affecting climate: Altitude

  - Temp decrease 1 degree/ 100m

  - Fewer solid particles in higher altitude to retain heat

  - Heat is lost rapidly to space
• Factors affecting climate: Aspect

  Northern Hemisphere:

  - south facing places face the sun

  - Get more sun and are sheltered from cold North winds

  - Warmer and lighter

  - north facing cooler and darker

  - More exposed to wind
• Factors affecting climate: Prevailing Winds


  - Winds blow in UK SW most often

  - Over land, wind is warmer in summer, cooler in winter

  - Over sea, wind is cooler in summer, warmer in winter

  - Wind is dry over land

  - Wind is wet over water
• Factors affecting climate: Ocean Currents

  - Britain has maritime climate

  - Warm ocean current from North Atlantic Drift
• Stages of rainfall


  - evaporated, warm air rises

  - as it rises it cools

  - and as it cools it condenses

  - to form clouds

  - if too heavy, these clouds produce rainfall
• Types of rainfall (3)

  - Convectional Rainfall

  - Frontal Rainfall

  - Relief Rainfall
• Convectional rainfall


  - the sun heats the ground and air above it

  - convection currents of warm air rise

  - the water vapour condenses forming clouds, and rain falls

  
• Relief rainfall


  - warm, moist air is forced to rise over high areas

  - air cools and condenses forming clouds

  - it rains

  - air descends, warms, and becomes drier over the other side

  
• Frontal rainfall


  - condensation forms clouds

  - warm air is forced to rise over cool air

  - it rains heavily along the front

  
• Types of clouds


  cirrus - wispy

  cumulus - heaped looking/fluffy

  stratus - layered sheets

  nimbus - low, grey rain cloud

  
• Anti-cyclones


  - HIGH air pressure

  - descending cool, dry air

  - clear weather

  - Synoptic chart: no weather fronts
• Cyclones/Depression


  - LOW air pressure

  - rising warm, moist air

  - cloudy weather

  - Synoptic chart: weather fronts
• Synoptic charts


  - measured cloud cover by observation

  - measured in oktas

  - 1 oktas = 1/8 sky covered in clouds

  
  

  tips for reading:

  - identify whether there are fronts, and if there is high or low pressure

  - read key carefully