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The Climate of the British Isles

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1 The Climate of the British Isles
Learning Objectives: Know the characteristics of the climate and British air masses Understand depressions Understand anticyclones Know a case-study of a storm event

2 Precipitation - Clouds
Know the characteristics of the climate and British air masses Precipitation - Clouds Clouds are formed by the condensation of invisible water vapour in the atmosphere. In being forced to rise, the air temperature falls below dew point temperature and water droplets result. Humidity and Dew point Humidity - a measure of the amount of water vapour in the atmosphere. Warm air can hold more water vapour than cold air. In humid weather the amount of water vapour being held is between 80-99% of the maximum it can hold i.e. it is saturated at 100%. Absolute humidity – The mass of water vapour in a cubic metre of air (g/m3) Relative humidity – The amount of water in the air at a given temperature (% of maximum e.g. 50% or below is dry air. Dew point – The temperature at which unsaturated air becomes saturated and water droplets begin to form (condensation).

3 Precipitation – Frontal rainfall
Tropical air warm air LCL cold air Polar air Note for teachers: LCL = Lifting Condensation Level - the level at which a parcel of moist air becomes saturated when it is lifted dry adiabatically. What are the stages in the formation of frontal rainfall? 1. Warm, moist air meets cooler, denser air. 2. Warm air is lighter, less dense and lower pressure so rises over the colder air, 3. The warm air cools as it rises, becomes saturated and rain begins to fall.

4 Precipitation - Relief rainfall
LCL LCL Rain shadow What are the stages in the formation of relief rainfall? 1. Air is forced to rise over a relief barrier. 2. Air cools as it rises and becomes saturated. 3. Water vapour condenses, forms droplets and falls as rain. 4. On the leeward side air warms as it sinks and precipitation ceases. What is the drier area on the leeward side called? the rainshadow

5 Precipitation - Convectional rainfall
LCL What are the stages in the formation of convectional rainfall? 1. Ground is heated and conducts heat to adjacent air. 2. Warm air rises and latent heat is released. The beginning of unstable cumulo-nimbus cloud developing in summer 3. Air cools as it rises and becomes saturated. 4. Water vapour condenses, forms droplets and falls as rain.


7 Quick information: The gulf stream influences the British climate. Water takes longer than land to heat but is slower to cool. Mountains and hills can cause relief rainfall Heat can cause convectional rainfall

8 Know the characteristics of the climate and British air masses
Describe and explain the pattern of rainfall in the British Isles. 8 marks What will the 8 marks be awarded for? Description – Explanation - Average yearly rainfall in Britain

9 Know the characteristics of the climate and British air masses
Average summertime surface temperature in Britain. Average wintertime surface temperature in Britain. Describe the differences in temperature between summer and winter in Britain. Explain the differences in temperature in the British summertime Can you explain why in the winter the isotherms run roughly east-west and in the summer they run roughly north-south?

10 AQA A2 page 48 fig 2.7 On a map of the British Isles use figure 2.7 and the text about wind to annotate your map with information about wind in Britain.

11 Influencing air masses in the British Isles
The UK weather continually changes because of the different weather systems brought by different air masses. Am What are the main air masses affecting the British Isles? Polar maritime (Pm) Pm Pc Tropical maritime (Tm) Tropical continental (Tc) Polar continental (Pc) Arctic maritime (Am) Tm Tc Prevailing wind direction AQA A2 page 50.

12 Know the characteristics of the climate
and British air masses Discuss the relative importance of the physical factors that influence the climate of Britain. 40 marks Use the essay generic mark scheme on the P:drive Essay style question – make notes, plan and write.

13 What do you know? Understand depressions What are depressions?
998 1002 1006 1010 The synoptic chart for a mid-latitude depression Isobars Cold front Warm front What are depressions? Large, LP surface weather systems. They are linked to upper air movements (Rossby waves) and are part of the global atmospheric transfer of energy. Which air masses are most likely to bring depressions to the UK? Tropical maritime/Polar maritime In a northern hemisphere depression, in which direction do the winds blow? Anticlockwise. They usually follow the isobars (lines of equal pressure).

14 Depression from above

15 Depressions Satellite image of a mid-latitude depression over the Atlantic. Synoptic chart of a mid-latitude depression over the Atlantic.

16 Cold wind Warm wind Warm air pushed up as its less dense.
Travelling faster than other side.  Tom Abbott, Biddulph High School and made available through and only for non commercial use in schools

17 Warm wind Cold wind  Tom Abbott, Biddulph High School and made available through and only for non commercial use in schools

18 Warm wind Cold wind  Tom Abbott, Biddulph High School and made available through and only for non commercial use in schools

19 Cold wind  Tom Abbott, Biddulph High School and made available through and only for non commercial use in schools

20 Depressions How and why do mid-latitude depressions form? cold air
Depressions originate at the POLAR FRONT - where the Polar Easterlies (cold air mass from the Poles) blow parallel to the Westerlies (warm air mass from the tropics). The depression begins when the cold air begins to undercut the warm air. warm air cold air A wave develops on the Polar Front. The warmer, less dense air is forced to rise in a spiral movement (due to coriolis effect). This means there is less air at the surface creating lower pressure. Winds begin to blow around it.

21 Depressions – characteristics
Low pressure <1000mb Steep pressure gradient from the outside to the centre Usually move rapidly W to E across UK Strong winds blow inwards in anticlockwise manner

22 Depressions – formation
Dense, moist, cold pm air meets light, moist, warm tm air Warm air is forced to rise over the cold air Rotational forces of the Earth cause the rising air to twist Twisting vortex creates a wave at ground level in the polar front cold front warm sector warm front Warm front is at the leading edge of the depression Behind this is the warm sector Following on is the cold front As the depression moves east (due to Rossby waves), the cold front catches up with and overtakes the warm front, creating an occluded front

23 Depressions – weather Rainfall Temperature
Warm front: As the warm Tm air rises over the cold Pm air, it cools via uplift and contact to dew point, there is condensation and rainfall. The rainfall intensifies as the WF approaches Warm sector: rainfall will stop Cold front: The cold air undercuts the warm air and causes more rapid uplift, therefore higher intensity and shorter duration rainfall Temperature As the warm air passes there will be a sudden increase in temperature. Once the CF has passed it become much colder Winds Veer from S/SE to SW to NW, becoming very strong as CF passes. Anticlockwise circulation into the centre Clouds Thicken and lower towards the WF, become scattered in the warm sector and become towering at the CF Pressure Decreases steadily to the center of the depression

24 Why these changes occur (the processes responsible).
An Integrated Approach page Read and take notes from the book about Depressions over the UK. The passage of a depression over the UK leads to predictable weather change over a period of time. Outline the changes that would occur over Liverpool in a 12 hour period if a mature depression passed from west to east. Refer to: Changes in wind speed and direction, cloud cover, temperature and precipitation. Why these changes occur (the processes responsible).

25 Depressions – Carlisle floods 2005
Case-study: storm events The UK, due to it’s mid-latitude position, is regularly hit by depressions that form out in the Atlantic and are driven westwards by Rossby waves (Polar front jet stream). On January 6Th 2005 an unusually low pressure weather system (depression) hit the UK. Gales and torrential rainfall lashed the NW of England causing extensive flooding, the loss of life and millions of £’s of damage. Carlisle, a town close to the Scottish border, and the surrounding area was particularly badly affected. Continuous rainfall for two weeks in late December was followed by the extreme weather from 6th to 8th January. 15% of the average rainfall fell in 36 hours (about 220mm). Winds of 90mph felled trees and by 2am on the 8th the rivers could no longer hold the vast amounts of water and Carlisle began to flood.

26 Carlisle floods - Effects
3 people died,1,600 homes flooded, estimated cost £100 mill 6,000 people had to be re-housed because of displacement 1,150 trees felled in the gales 70,000 people without power for 3 days Rail services cut for 2 days, roads and bridges closed for 2 days 70 buses lost worth £3 million Ind. Est.flooded damaging 325 business properties- cost £100 million Fire station flooded, relocated to Carlisle Castle Emergency centres set up in a school and church hall to receive rescued residents, ran for 5 days Phone exchange flooded, mobile phone mast down, Radio Cumbria becomes main source of information and broadcast throughout the crisis RAF, Coastguard and Mountain Rescue teams evacuate people by boat and helicopter

27 Carlisle floods – The future
Reappraisal of flood defence needs for the city, works expected to last 3 years costing £20 million • Plans to rebuild Police station on a new site • Plans to significantly alter city centre • Many small family firms closed down • A year on some flood victims still in temporary housing • Increases in household and car insurance premiums throughout the Carlisle postcode area Home learning: Complete some additional research about the Carlisle floods in 2005, get some photos and annotate them. What other storm events have occurred? How were they dealt with?

28 Group exam answer Create notes from your work and home learning
Group exam answer Create notes from your work and home learning. Plan out the essay write the essay. Discuss the impact of storm events in the British Isles and evaluate the responses to them. 40 marks (A2 exam 2010)

29 Anticyclones clockwise Understand anticyclones
An area of high pressure. Bring stable conditions with clear skies. In the UK they are associated with extended warm, dry conditions in the summer and cold, frosty and sometimes foggy conditions in the winter. An anticyclone may be 2500 km in diameter, although many are smaller. 1032 1028 clockwise The synoptic chart for a mid-latitude anticyclone The satellite image shows the cloudless skies associated with high pressure systems. They may remain for a number of weeks causing heat waves across many parts of Europe during the summer.

30 Anticyclones Anticyclonic Weather In The UK
Winter Conditions (Polar Source) Summer Conditions (Tropical Impacts Conditions Ice. Increase in accidents particularly elderly increased power use. Cold day time conditions. Usually below freezing. Hot daytime conditions over 23º. Increase in heart attacks/heat stroke. Sales of lettuce/ice cream/ soft drinks increase. Hose pipe bans/drought. Roads need gritting. Very cold at night with frosts. Warm night temperatures. Sleeping difficulties. Temperatures remain low. Clear skies. Generally clear skies. Sunburn/ sunstroke. Car accidents. Disruption to transport (aircraft, ferries). Stable conditions may produce fog. Some early morning mists especially at coast. May take a while to clear impacted tourists. Breathing difficulties. High levels of pollution due to lack of wind. Thunderstorms may form in evenings due to convection. Flash flooding effects homes and transport. Hospital admissions increase. Subsiding air traps pollutants. Photo-chemical smog and low ozone level trap heat. Increase in deaths from asthmas/breathing conditions.

31 European heat wave of 2003 Use the website to create a study sheet about anticyclone weather and the heat wave of 2003.

32 Winter anticyclones Read page 54 AQA A2 text book.
State the characteristics of a winter anticyclone and give reasons for these. You can draw labelled diagrams to help you answer.

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