Weather systems in mid-latitudes and their interaction with human environments

1. Weather systems in mid-latitudes and their interaction with human environments Winter & summer anticyclones and associated weather

2. Anticyclones • Definition: An anticyclone is a large mass of subsiding air which produces an area of high pressure on the earth’s surface. • Source of subsiding air is upper atmosphere • Air warms at DALR as it descends • Pressure gradient weak as it is one air mass • Winds light & clockwise blowing outward from centre • May be 3000km diameter

3. Anticyclones can block depressions – once established can give several days (or in extreme cases weeks) or settled weather.

4. Polar Front moves north and Azores high pressure system extends northwards to cover much of UK No cloud Intense insolation Hot sunny days (up to 30C in S) Dry Calm – build up of pollutants in lower atmosphere – ozone, pollen, nitric oxides Any wind is southerly bringing in polluted air from mainland Europe Rapid radiation cooling at night Temperature inversions Dew & mist (rapidly clear in morn) Coastal areas – advection fogs & land sea breezes Highlands – mountain & valley winds If source Tc (N Africa) then heat wave conditions Increased risk of thunderstorms & Spanish Plume (East Anglia and SE) Blocking anticyclones occur when high pressure cell detaches from the sub tropic high and stays for long time & block depressions – leads to drought conditions Summer Anticyclone

5. Cold, dense air flows down adjacent slopes and collects on valley floor.Low wind speeds or calm conditions needed.

6. Polar Front moves southwards and polar high pressure system moves southwards to dominate over UK Little insolation due to the low angle of the sun Night – low temp, temp inversions, ground frost, radiation fog, freezing fog – most noticeable inland Longer to disperse in morn due to weak sun When pollutants mix with fog it forms smog – now rare in UK due to Clean Air Act 1956, but in Dec 1952 The Great Smog of London indirectly killed c. 4000! Pc – source central Asia, moves over cold land mass – cold, dry, stable. Over North Sea gets warmth & moisture – can cause heavy snow on the East coast. Winter Anticyclone

7. Weather & People • Any weather will have an effect on economy of a country and society in general e.g. hours worked, communication systems, migration & life itself. • Effects on people: • HEALTH ISSUES Disease - most likely in Spring & Autumn due to change in temp e.g. measles & colds are common during this period. Psychological issues – people get depressed during long dark winters, increased suicides in spring as others celebrate new life, more crime in summer as people get aggravated. Elderly cannot afford to heat their homes properly in winter (homeless people)– hypothermia. Heat stroke and sun burn in summer. Respiratory problems brought on by smog. Very cold weather helps to kill germ.

8. Weather & People 2. SOCIAL ISSUES: • Amount of hours spent at work – very long hours for some outdoor jobs in summer • Working conditions – increased heat in building due to double glazing, central heating – people more irritable • Quicker spread of disease in air conditioned buildings • More social life style in summer – eating, drinking out doors, more relaxation • Canopies or heaters can be used outdoors e.g. parasols and patio heaters in summer • Fetes, festivals held in summer months – winter less eventful, less to look forward to. • Seasonal change in our diet – fruit & veg. in season, more cold food (salad) eaten in summer, more soups and hot drinks in winter, ice cream sales • Different clothing worn in different seasons – retail driven by the weather • Long school holiday taken in summer because weather better and every one finds it more difficult to work and concentrate in the heat • Hose pipe bans affect gardeners, swimming pool owners • Coastal damages due to waves during storms • Filling of reservoirs and groundwater storage – good for home owners and farmers • Loss of electricity due to winds

9. Weather & People 3. AGRICULTURE - Weather dictates choice of crops • Several months of year when nothing grows • Aspect (S facing slopes) influences what crops are planted where – fragile plants would not be grown on valley floor as frost hollows are created there • Green houses used to counterbalance weather • Crops covered in plastic to encourage germination and early growth, portable heaters - Wind breaks planted to protect crops • Canopies or heaters can be used outdoors e.g. parasols and patio heaters in summer • Intense r.f. or hail can destroy crops (flatten, flood) • Animals brought inside in winter, out in fields in summer • Number of farms and farmers in decline due to long hours of work out in the elements • Crop failure due to drought if prolonged summer anticyclone • Need for irrigation

10. Weather & People 4. TRANSPORT -black ice on roads very dangerous -Glare from sun accounts for 25% of all road accidents -strong winds mean bridges may be closed due to risk to high sided vehicles, roads closed due to fallen trees -heavy snow fall – roads (chains on tyres, people by 4 wheel drive, heated roads to hospitals), airports closed, weight on roofs – buildings collapse, skiing, sledging -sea travel – storms dangerous, calm weather slows sailors -flights to USA use jet stream (return journey quicker, less fuel needed) -rail travel – freeze-thaw cycles can buckle tracks, metal also corrodes

11. Exam questions • You need to identify the disadvantages and advantages of the weather associated with each weather system - depressions and anticyclones. • You need to be able to clearly describe the sequence of weather associated with each and then how each affects human environment. • Good to use examples of each such as Great Storm of 1987 (depression) and Great UK Drought of 1976 (anticyclone).

12. Essay questions – past papers(12 marks) • Describe and explain how the weather experienced during both winter and summer anticyclones in mid-latitudes affects the human environment. June 2005 • Discuss how low pressure systems in mid-latitudes interact with human environment. Jan 2004 • Describe and explain the weather changes associated with the passage of a frontal depression in the mid-latitudes. May 2003