Weather vs Climate
- Weather is the short term condition of the atmosphere in a given location.
- Climate is the long-term, average condition of the atmosphere for a location.
Elements of weather + how they are measured
Temperature: thermometer, F or C, Isotherm
Pressure: barometer, bar or Pa (Pascals), Isobar
Humidity: hydrometer, Percentage, Isohumes
Rainfall: rain gauge, mm
Wind direction: wind vane, km/h, Isotach
Sunshine: sunshine recorder, hours (h), Isohel
Anticyclones
An anticyclone (or high) is a wind system rotating around an area of high pressure. It forms when a large mass of air cools down rapidly and descends, increasing surface pressure. As the air descends it warms and is able to pick up more moisture, which is then blown outwards (clockwise direction in NHS, counter-clockwise in SHS), resulting in dry and settled conditions with clear skies.
Rainfall
Rainfall results from warm air, which contains water vapour, rising and cooling down. Cold air cannot hold as much moisture as warm air: as the air continues to cool down and rise, it reaches the dew point, and the water vapour condenses into droplets (rain).
Types of rainfall
- Frontal: Associated with depressions. Occurs when warm, moist air meets cold, drier air. As the two air masses have different densities, they can't merge, and the light warm air is forced to rise over the cold air.
- Relief: occurs when warm, very moist air from the sea is blown inland towards a mountain barrier. The air will be forced to rise over it and will cool, resulting in condensation and rainfall if dew point is reached.
- Convectional: occurs when the ground surface is heated, heating the air adjacent to the ground, causing it to rise. As the air rises, it cools and water vapour condenses, forming heavy storms.
Depressions
A depression (or low) is formed by a large warm air mass rising, thus forming a low pressure area. Pressure is lowest at the centre of the depression. Surrounding air masses from will spiral inwards (counter-clockwise in NHS, clockwise in SHS). Depressions bring rain, cloud cover, and wind.
Fronts
When warm, light, moist air meets cold, heavier, dry air, the two air masses do not mix easily due to their different densities and temperatures. The boundary between these two air masses is called a front
- Warm front: occurs when warm air moves towards colder air, and is forced to rise over the cold air. Brings steady rainfall, cloud cover and strong winds.
- Cold front: occurs when cold air moves towards warmer, lighter air and undercuts it, forcing it to rise. Brings heavy cloud cover and short rainfall periods.
- Occluded front: as the cold front travels faster than the warm front, it catches up with it. Brings a drop in temperature, some cloud cover and rainfall.
The atmosphere
The atmosphere is the layer of gases surrounding a planet. Earth's atmosphere is divided into 5 layers.
- Troposphere (0-10km): the lowest layer of Earth's atmosphere. Almost all weather occurs within this layer. Temperatures drops with increasing altitude.
- Stratosphere (10-50km): the second lowest layer, that contains ozone (an oxygen molecule), which absorbs energy from solar UV radiation, heating the stratosphere. Temps. rise with increasing altitude.
Factors affecting temperature
- Latitude: Places nearer to the Equator are much warmer than places towards the Poles.
- Distance from Sea: as land heats and cools down rapidly than the sea, inland areas will have warmer summer and colder winters than coastal areas.
- Prevailing winds: The seasonal difference in heating between land and sea also affects the temperature of the prevailing winds (when and from where they blow).
- Ocean currents: classified as being warm or cold, they affect the climate and temps. of coastal areas.
- Altitude: temp. decreases with height (1°C every 100 m), so mountains are much colder than lowlands.
Type 5: Hot desert climate
Hot deserts are characterised by high temperatures, a large annual range (25°C) and a large diurnal range, with temps. reaching up to 50°C during the day, around freezing at night. Annual rainfall is low (less than 250mm), which is caused by the dryness of the prevailing winds (blow from land/cross mountains). This climate can mostly in the horse latitudes on the west coast of continents (apart from the Sahara). There is very low biodiversity, with vegetation mostly consisting of cactuses.
Type 4: Cold Climate or Tundra Climate
Cold climates are characterised by a very large annual temp. range (-18/22/40°C) , with very cold winters (days are significantly shorter) and relatively warm, short summers (days are significantly longer). Precipitation is light (300mm annual) as the air is too cold to hold moisture and most places are landlocked.
This climate is mostly found to the polewards side of 60°N in Eurasia and North America (Polar Belt). The vegetation mostly consists of coniferous forests.
Human activities in chosen climate types
- Hot desert: Tourism, solar power, mining (ex: limestone or marble). Challenges include extreme temperatures and limited water supply.
- Cold Climate: extraction of fossil fuels such as gas and oil (abundant in cold environments), fishing. Challenges include deforestation, destruction of natural habitats and contamination (leaks of heavy metals or other substances).