What am I describing?
Some people love this, others hate it.
40,000 people died in Europe because of it in 2003
It always occurs in summer
Usually associated with high pressure, sunny, dry
weather.
Anticyclones, depressions, hot &
drought, cold & snow
Learning Objectives:
•To describe and explain the weather associated
with high and low pressure systems
•Link them to extreme weather, list the hazards
associated with this extreme weather and assess
their impacts on various sectors of the community.
The Global Circulation:
•Weather is driven by the unequal heating of the Earth’s
surface.
•Air heated strongly at the equator becomes less dense
and rises, reaching the top of the troposphere (10-15km)
and then it spreads outwards to both poles.
•When it reaches the Polar Regions, it sinks and through
continuity flows back to the equator.
• This closed cell of circulation creates a low pressure at
the surface where air is rising (i.e. at the equator) and a
high pressure where air is sinking (Polar Regions).
The Global Circulation Continued:
However, due to the Earth’s
rotation, the circulation is
more complex and actually
results in three separate
circulations .
Adding further to the
complexity is the nonuniform nature of the Earth’s
surface (sea, land,
mountains, ice etc).
Video explanation
NASA - 1
Animation
Anticyclones
A large area of high atmospheric pressure,
characterised by outward-spiralling winds - a
"high". Winds are clockwise in the Northern
Hemisphere and anticlockwise in the Southern
(Source: BBC).
Isobars – Lines of equal
pressure
Direction of surface winds
High pressure with pressure
in millibars
H 1034
This animation shows the
affect of the Coriolis force.
Although the air moves from
high to low pressure, the
rotation of the Earth makes it
appear deflect to the right
from the point of view of an
observer on the Earth.
H
Anticyclones continued
•Anticyclones are masses of sinking air creating a
high pressure (>1013mbars) at the surface.
•Horizontal pressure gradients (how much
pressure changes with distance) are often small
and so the surface wind speed is usually low.
•The sinking air inhibits convection and therefore
cloud formation, so hot, dry days usually
accompany high pressure systems in summer and
cold, dry days in winter.
Cyclones
•A large area of low atmospheric
pressure, characterised by
inward-spiralling winds - a "low" also called a "depression".
•Winds are anticlockwise in the
Northern Hemisphere and
clockwise in the Southern
(Source: BBC).
•Cyclones consist of rising air,
creating the low pressure
(<1013mbars) at the surface.
Formation of
a cyclone
Direction of
surface winds
L 984
Low pressure centre with
pressure in millibars
Cyclones continued
•Horizontal pressure gradients can be very steep and so
the surface wind speeds are often high and sometimes
extreme.
•The rising air promotes convection and cloud formation
and therefore precipitation (rain, snow, hail etc).
•Weather fronts (the boundary between different air
masses) are formed with cyclones.
A weather map showing a
complex situation of high
and low pressure weather
systems across the US.
Source NOAA - 2
Weather symbol for a cold front
Cold Front – The boundary between cold and warm air,
where cold air is undercutting the warm air (because it is
denser). This lifts the warm air, possibly to a level where
it can rise by itself (convection) due to instability in the
atmosphere, resulting in clouds and rainfall.
Cold fronts often bring heavy rain, cooler air, and a
clockwise shift in wind direction (veering wind).
NASA -3
Animation of
a cold front
Weather symbol for a warm front
Warm Front – The boundary between cold and warm air,
where warm air is overriding the cold air (because it is
less dense). This air rises steadily, but again may result in
convection occurring.
As warm fronts pass through a location they bring
warmer air, cloud, rain and a veering of the wind.
NASA -4
Animation of
a warm front
Weather symbol for a warm front
Occluded Front – These occur when a cold front catches
up a warm front and undercuts it. Various types of
weather can be associated with an occluded front
including thunderstorms, rain, cloud or very little
apparent change. Normally the air at the surface becomes
drier.
A cyclone showing
the position of each
of the fronts
Animation of
an occluded
front
NWS -5
Triple Point
On your map of Europe, draw in pencil the
position of an anticyclone which could lead to
hot weather in the UK.
Hint: Think of the direction the air coming into
the UK should be from.
Answer – Anticyclone over the North Sea area and
extending across the UK. This gives Southerly or SouthEasterly winds bringing hot, continental air into the UK.
A cyclone to the South West of the UK would also be
likely to occur, further enhancing the Southerly wind.
Social:
•Death
•Hyperthermia (heat stroke)
•Heat rash
•Heat cramps
•Heat exhaustion
•Pressure on NHS and other health services
•Cancellation of outdoor activities
•Difficulty sleeping
•Power cuts due to excess air conditioning use.
•Water shortages/hose pipe bans
Economic:
Video
•+ Shops sell extra ice-cream, bbq, salads, drinks
•+Electricity companies boost sales due to air
conditioning, fans etc
•+Seaside resorts see increase in sales/demand.
•-Cinema’s and other indoor activities lose out
•-More ‘sick’ days taken during hot weather
•-Damage to transport network e.g. Train lines
bending in the heat
•-Crops damaged or destroyed by heat/drought
The overall effect on economy is uncertain
Environmental:
•Stress or death to wild and farmed animals.
•Crops and trees damaged or killed by heat and
drought
•Rivers run low or dry, leading to loss of species
•Extra irrigation of land could lead to increased
soil salinity.
•People making extra journeys to the beach etc
and using air conditioning leads to increase in
greenhouse gas emissions.
•>40,000 people dead across Europe due to the heat wave
•38.5oC (101.3oF) recorded in Brogdale in Kent, UK
•48oC (118.4oF) recorded in Amareleja, Portugal
•France lost 20% of its wheat crops due to drought
•UK rail transport severely disrupted by speed limits
imposed on railways as the heat caused some rails to
buckle.
•215,000 hectares of forest destroyed in Portuguese fires –
an area the size of Luxembourg!
•The river Danube in Serbia fell to its lowest level in 100
years exposing world war two relics.
•Two nuclear power stations were forces to close due to
cooling issues.
•Cost to European farming estimated at 13.1billion Euros.
•The London Eye closed for a day after cabin
temperatures became unbearable.
UNEP – United Nation Environment
Programme – European heat wave review
% of expected rainfall
totals in the UK for Feb –
Oct 2003.
Orange areas –
Substantially below
average
Red areas – exceptionally
low rainfall
Source: UK Met Office - 6
Satellite image of forest
fires in Portugal –
Source: UK Met Office
7
Following this heat wave, the Met Office set
up a warning system to prepare the public and
health service etc in advance of an imminent
heat wave.
Met Office Heat-Health Watch (only available 1st
June to 15th September)
On your map of Europe, draw in pencil the
position of an anticyclone which could lead to
cold weather in the UK.
Hint: Think of the direction the air coming into
the UK should be from.
Answer – Anticyclone to the west of the UK. This gives
Northerly winds bringing cold, Arctic air into the UK. A
cyclone in the North Sea would also likely occur (called a
Polar Low), causing weather fronts bringing snow and
high winds. OR High to NE of UK and low to S bringing
in strong, cold Easterly winds from the continent.
Frost on a windscreen - 8
Frost
During anticyclonic
weather in winter,
skies are often clear at
night. The ground then radiates heat straight out
to space. The ground therefore cools rapidly and
causes the air around it to also cool.
The air may reach temperatures below 0oC and
below its dew point. This means ice will form onto
surfaces (such as grass) – i.e. frost.
South Dakota
Blizzard 2008
A satellite image showing
the UK almost entirely
covered in snow 07-01-10
NASA - 9
Blizzard
Definition (Met Office):
•30mph winds
•Moderate or heavy snow
•Visibility below 200m
A cyclone brings weather fronts with moist
air, precipitation and strong winds. If these
move into cold air or the cyclone comes from
a cold region then snow will fall. Often the
criteria above are reached and a blizzard
therefore formed.
What social, economic and
environmental issues are
associated with cold spells?
Social:
•Death
•Hypothermia
•Travelling difficult for elderly and disabled
•Outdoor activities cancelled or postponed
•Increase in admittance to A&E
•+Parents may spend more time with their
children if schools are closed
Economic:
•Workers stuck at home
•Childcare costs when schools are closed
•Damage to infrastructure e.g. Road surfaces, downed
power lines. Airports, railways & roads closed.
•Extra winter fuel payments to elderly costs the
government.
•Cost of road gritting/salting
•Pipes freeze and crack
•Damage or death to less cold-tolerant crops such as
citrus fruits
•Increase in warm weather clothes sales
•Gas and electricity companies increases profits as
demand increases
Environmental:
•Increased road gritting/salting pollutes the
environment
•Widespread death of animals due to lack of food.
•Extra greenhouse gases emitted as people try to
stay warm by burning fossil fuels.
ITN News Report
•The coldest winter for England and Wales since 19781979
•Mean winter temperature was 1.6oC (2.1oC) below the
1971-2000 average.
•Grit supplies ran out in some council areas. 60,000
tonnes of salt were being used per day.
•A gas supply alert was made to ensure supplies in the UK
were maintained. This meant turning the supply off to
major industrial users who had signed up to interruptible
contracts.
•The temperature fell to -22.3oC at Altnaharra, Highland.
•1000 vehicles were stuck on the A3(M) as over 12inches
of snow fell on 6th January.
•Over 8000 schools were closed on the same day and
5000 homes in Sussex were left without electricity.
•Hampshire council called on 120 farmers to help clear
roads
•All outpatient appointments and non-urgent operations
at hospitals covered by the Oxford Radcliffe Hospitals
Trust were postponed.
•The Royal Berkshire Hospital in Reading sent midwives
out in 4x4’s to help women in labour.
•Football, horseracing and many other sporting fixtures
were postponed.
•100’s of flights were cancelled to and from UK airports
including Heathrow and Gatwick.
Met Office chart showing all of the UK
with negative temperature anomalies
for the 2009-2010 winter compared to
the 1971-2000 average.
10
1. Anticyclone
2. Cyclone
3. Coriolis
4.Cold front
5. Warm front
6.Occluded front
7. Hyperthermia
8. Hypothermia
9. Frost
10. Blizzard
11. Clockwise
12. Anticlockwise
Sources:
1) NASA - http://sealevel.jpl.nasa.gov/overview/images/6-cellmodel.jpg
2) NOAA - http://aviationweather.gov/adds/progs/
3) NASA - http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html
4) NASA - http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html
5) NWS http://www.srh.weather.gov/srh/jetstream/synoptic/cyclone.ht
m
6) UK Met Office - http://www.nercwallingford.ac.uk/ih/nrfa/yb/yb2003/drought2003/fig4.html
7) UK Met Office http://www.metoffice.gov.uk/education/teens/casestudy_heat
wave.html
Sources:
8) Authors own photo
9) NASA - http://rapidfire.sci.gsfc.nasa.gov/gallery/?20100070107/GreatBritain.A2010007.1150.1km.jpg
10) UK Met Office http://www.metoffice.gov.uk/climate/uk/2010/winter.html