Weather and climate

• Circulation cells


  Three circulation cells in each hemisphere that redistribute heat energy
• Hadley cells


  Warmed air rises at the Equator, divides, cools and moves north and south, sinking at 30° north and south
• Ferrel cells


  Some of the cooled air moves back towards the Equator as trade winds, the rest travels towards the Poles
• Polar cells


  Warmer air of the Ferrel cells meets colder polar air, the warmer air rises to form Polar cells that travel to the Poles, cool and sink
• Oceanic circulation


  Wind-driven surface currents and deeper ocean currents move warm water towards the Poles and colder water towards the Equator
• Colder, denser water at the Poles sinks and flows towards the Equator as cold ocean currents. Less dense water from the equatorial areas flows as warm surface currents to replace this cold water. This process is repeated, causing heat energy to be transferred from the Equator to the Poles.
• The Quaternary period covers the last 2.6 million years, when there have been more than 60 cold periods with ice advances, lasting about 100000 years and warmer interglacial periods lasting about 15 000 years.
• In the last 250 years the Earth's temperature has risen significantly compared to before. Average temperature in the middle of the last Ice Age was about 5°C below today's average temperature.
• Milankovitch cycles


  Long-term changes to the Earth's orbit and position, changing how much solar radiation the Earth receives - resulting in changes in climate
• Milankovitch cycles


  • Eccentricity cycle
  • Axial tilt cycle
  • Precession cycle
• Growth rings from trees can provide evidence of past climate change. Wider rings indicate a warmer, wetter climate and thinner rings indicate a colder, drier climate.
• Volcanic activity can cause climate change by ejecting ash and dust into the atmosphere, which acts as a blanket over the Earth, blocking out solar radiation and causing temperatures to fall for a time.
• Human activity releases increasing levels of CO2 and other greenhouse gases into the atmosphere, increasing the greenhouse effect and causing more warming.
• Melting ice sheets and retreating glaciers add water to oceans, making sea levels rise. Arctic melting could cause the Gulf Stream to move further south, leading to colder temperatures in Western Europe.
• Climate change means that longer periods of drought could lead to lower crop yields in some regions, potentially causing food shortages.
• During the Medieval Warm Period (950-1100) higher temperatures meant greater crop yields and a growing population. This was due to increased solar radiation.
• During the Little Ice Age (1600-1685) temperatures were low enough to freeze the Thames, due to increased volcanic activity and decreased solar radiation.
• Maritime influence


  Most of the air reaching the UK contains lots of moisture, as we are surrounded by sea, leading to rainfall all year
• Prevailing wind


  The main or prevailing wind for the UK comes from the south-west, bringing moisture and leading to more rainfall
• North Atlantic Drift


  This ocean current brings warm water north to the UK, making the climate milder than would be expected for its latitude
• Atmospheric circulation


  The UK is near the boundary between the northern Ferrel and Polar circulation cells, where warmer and cooler air meet, causing unsettled weather
• Altitude


  The higher an area is, the cooler and wetter it is, so there are significant regional variations within the UK
• The North Atlantic Drift brings warm water north to the UK, making the climate milder than would be expected for its latitude.
• Tropical cyclones need a source of warm, moist air and warm ocean temperatures (27°C plus) to form.
• Tropical cyclones are more likely to happen in the northern tropics from June-November and in the southern tropics from November-April.
• Tropical cyclone characteristics


  • Very low pressure
  • Form a cylinder of rising, spiralling air surrounding an eye of descending, high-pressure air
  • Cloud banks called the eye wall surround the eye
  • Often 400 km wide and 10 km high
• Tropical cyclone movement is determined by the prevailing winds and ocean currents, and their track is influenced by how far they travel over the ocean.
• The Saffir-Simpson scale classifies tropical cyclones into five categories based on wind speed.
• The most important measurement used to decide the category of a tropical cyclone on the Saffir-Simpson scale is the wind speed.
• Typhoon Yolanda in November 2013 had maximum recorded wind speeds of 315 km/h, with average speeds of 280 km/h, which would classify it as a Category 5 tropical cyclone on the Saffir-Simpson scale.
• Major devastation


  • Destroys buildings, floods up to 10 km inland
• Catastrophic destruction


  • Up to 5 m above sea level. Mass evacuation needed
• The maximum recorded wind speed for Typhoon Yolanda (November 2013) was 315 km/h, with average speeds of 280 km/h.
• What category was this tropical cyclone on the Saffir-Simpson scale?
• Hurricane Sandy travelled across the Caribbean Sea, affecting the island nations of Jamaica, Cuba and Haiti, before moving north to reach the USA.
• It reached New Jersey on 29 October 2012.
• By the time the hurricane reached land, wind speeds of 129 km/h were recorded.
• The storm surges caused most of the damage to East Coast states.
• The use of social media such as Twitter and photographs uploaded to Flickr helped with damage assessment.
• Death toll of at least 150 people