Evaluation of the Storm For the South of England to be hot by such winds again is thought to be a 200 year event However, such an event occurring in the North of England most likely has a year return period It is clear that an expected loss of £4 billion (in today’s money) in the U.K. is not that unusual, with a return period for exceedance of only around 35 years. Indeed, insurance loss estimates from other noteworthy storms exceed this value. Weather forecasting was not accurate enough. Some would see this as a criticism, others point to the unpredictable nature of the weather (unforeseen deepening of the depression), and the lack of technology at the time. Could more money have been spent on up to date weather tracking systems? Possibly yes. Since 1987, there has been investments in new technology. Supercomputers now allow models from to be more specific (80km then to 1 and half km now). Models were run 2 times a day, now this is done 4 times. Automated buoys allow better tracking of off shore systems. The setting up of the National Weather Warning system. This consists of a national chain of met office employees on the ground who not only aim to predict the weather, but work with people such as councils and the environment agency to plan ahead

Some people felt that tree damage was partly due to lack of maintenance. Councils now take better care of trees. Register of trees, regular pruning, cutting down those which are unstable Emergency services were overwhelmed by the number of calls. The responses were criticised. Emergency services unprepared and communication systems outdated. Civil Contingencies Act was brought in to statute in 2004 which forced emergency services to communicate with the public. Closer links with met office allowing extra staff to be drafted in. New technology and central response centres allow better co- ordination of a response as opposed to multiple local stations

Anticyclones Describe and explain the UK weather in summer and winter associated with anticyclones

What????? Anticyclones are large areas of settled stable air, which bring settled weather to the UK. Descending air from the Jet Stream causes high pressure. Because they consist of one large air mass, they do not exhibit the complexity of depressions

Summary

Sketch a copy of the anticyclone below. Remember anticyclones form as a result of air piling up aloft. This encourages air to subside / sink down. As the air sinks, it warms, this increases the amount of water the air can hold, and thus keeps the sky relatively cloud free. Leading edge

Depressions and anticyclones Anticyclones form by the same processes that we discussed for depressions. Jet Streams!!!!!!!!!!!!!!!!! Anticyclones stay in place for long periods of time, days or even months. They are bigger in size than depressions

How???? Area of high atmospheric pressure caused by descending air, which becomes warm and dry. Winds radiate from a calm centre, taking a clockwise direction in the northern hemisphere and an anticlockwise direction in the southern hemisphere. Anticyclones are characterized by clear weather and the absence of rain and violent winds. In summer they bring hot, sunny days and in winter they bring fine, frosty spells, although fog and low cloud are not uncommon in the UK. Blocking anticyclones, which prevent the normal air circulation of an area, can cause summer droughts and severe winters.

Anticyclones are characterised by: High pressure readings in the middle. Far apart isobars = calm wind. The air subsides (sinks). It warms adiabatically which leads to a decrease in relative humidity = lack of cloud & dry conditions. Air moving away from the centre of the high. Air spins clockwise around from the high. They normal travel to the British Isles from mainland Europe. High pressure systems form commonly over the Azores – ‘Azores High’.

An Anticyclone

1 - Winds blow clockwise and out from the centre (where it is descending). 2 - These systems move slowly and can last for weeks over the UK. Low pressure systems (depressions) cannot move these high pressure systems out of the way, so move around them. 3 - There is a low pressure gradient, shown by the fact that the isobars are far apart, so there is also little wind movement. 4 - The highest pressure is in the centre of the system. 5 - There are three types of anticyclone in the world. The type over the UK is called TEMPORARY. The others are PERMANENT (sub- tropical e.g. Azores High) and SEASONAL, such as those over Eastern Europe and Russia in the winter when there is a large, cold land mass so the air descends as it is cooled, giving high pressure.

Depression and Anticyclone

Dep v anti (2) The isobars are close together in a depression, high pressure gradient = wind The opposite occurs in the anticyclone Notice the anticyclone moving in a clockwise direction. Depressions go anti-clockwise

Anticyclones and associated clouds

Anticyclones give rise to different conditions, depending on the time of year. Winter Cold day time temps, from below 0 o c to 5 o c Very cold night time temps – frosts below 0 o c Generally clear skies by day & night Summer Hot day time temp, over 25 o c Warm night time temps May not fall below 15 o c Generally clear skies by day & night

Winter Low level cloud may linger and radiation fog may remain in low lying areas Causes high levels of air pollution in urban areas as pollutants are trapped by temperature inversion Summer Hazy sunshine in some areas Early morning mists which disperse quickly Heavy dew in the mornings East coast has sea frets or haars (onshore winds) Thunder storms can occur when RH is high (Spanish Plume) Anticyclones give rise to different conditions, depending on the time of year.

Anticyclones – A Hazard? Think about the weather associated with an anti-cyclone. Why might they pose a hazard as great as that of a depression?

Anti-cyclones good….

Or bad?

FOG Comes in many forms…..

WHAT YOU NEED TO KNOW Definition of fog Under what conditions does fog form? The different types of fog

Definition Natural phenomenon that can be regarded as a hazard. It is an obscurity at the surface where visibility is below 100m. It is water suspended in the surface layer of the atmosphere. MIST = Less dense fog

Airlines <1000m visibility = fog 1000m-2000m = mist HAZE = Obscurity caused by dust or smoke. Cooling of mist leads to dense fog, cooling of haze does not SMOG = Fog mixed with smoke or pollutants such as sulphur dioxide. Reaction between sunlight and oxides.

For Fog to Form….. Air MUST be moist (close to saturation) The air must be forced to cool How it cools makes different types of fog Fog is essentially a cloud

Radiation Fog Radiation fog is formed by the cooling of land due to long wave radiation along with conditions of clear sky. The cool ground then produces condensation in the nearby air. In perfect calm the fog layer can be less than a metre deep but turbulence can promote a thicker layer. Radiation fog is common in autumn/winter and usually does not last long past sunrise unless sunshine is particularly weak

Advection Fog Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area with significant snow pack. It's most common at sea when tropical air encounters cooler higher-latitude waters, or in areas of upswelling, such as along the California coast. Common in summer anti- cyclones where the land is much hotter than the sea

Advection Fog

Up Slope Fog When air tries to move over a terrain obstacle, it cools to some degree as it rises, the degree of cooling depending on the amount of rise. During that cooling, if the air temperature falls below the dew point, the resulting condensation will form a cloud. If that cloud hugs the ground, it becomes fog at that surface. For example, an air mass moving over a water body may gain moisture until it is very near its saturation level. While still over the water, it may not cool enough to reach condensation, but when forced over the shore, the rise from water level may cause enough cooling to form a cloud/fog.

Valley Fog Valley fogs form when the air near the terrain heights cools — usually by radiation at night — and descends through its greater density into the surrounding valleys, flowing like water. Pooled in the valley, the cold air may condense the water vapour present into a fog which fills the valleys to a depth. E.g. Temperature Inversion

Precipitation Fog This fog type generally occurs when rain falling from warm air aloft evaporates at or near the surface under light wind conditions. The evaporating precipitation as it falls through colder air thus increasing the surface air's moisture burden until condensation is achieved.

DEW As air cools, it has the ability to hold less moisture Leaves may be colder than the surrounding air, and so any ‘vapour’ touching it may condense and form dew. The lowest few inches of the atmosphere are likely to have more moisture than that above it. Where does this come from? Explain why wind makes dew unlikely to form?

DEW

FROST NOT simply Dew that gets frozen SUBLIMATION (Vapour – Ice) Gas – Solid missing out the liquid stage

FROST Calm winds Temperature below freezing at grass level Radiation cooling (clear skies) 100% relative humidity

2003 Heatwave

Why? This is a weather map for midday on 5 August It shows an area of high pressure over most of western Europe. Air is moving around the high in a clockwise direction, brings a hot, dry tropical continental air mass to the UK at this time. This pattern occurred for much of the rest of the month. High pressure areas usually bring little cloud and warm conditions in summer.

Brodgale in Kent hit 39 degrees C (UK record) The heatwave lasted almost 2 months June-Aug

Human effects Heat-stroke - normally we sweat, and this keeps us cool on hot days. On very hot days our bodies may not be able to keep cool enough by sweating alone, and our core body temperature may rise. This can lead to headaches, dizziness and even death. Dehydration - this is the loss of water from our bodies. It can cause tiredness and problems with breathing and heart rates. Sunburn - damage to the skin which can be painful and may increase the risks of getting skin cancer. Air pollution - it is thought that one third of the deaths caused by the heatwave in the UK were caused by poor air quality. Drowning - some people drowned when trying to cool off in rivers and lakes.

Environment and social effects Water supplies - drinking water supplies were affected in some parts of the UK and hosepipe bans introduced. Tourism - many parts of the UK reported increased levels of tourism as people decided to holiday in the UK while the weather was unusually dry and hot. Agriculture - many chickens, pigs and cows died during the heat in Europe and crops failed in the dry conditions. This led to higher food prices. It is thought to have cost European farming 13.1 billion euros. Transport - some railway tracks buckled in the heat. The London Underground became unbearable. Some road surfaces melted. Low river levels prevented some boats from sailing. The London Eye closed on one day as it became too hot in the cabins. Energy - two nuclear power plants to close down in Germany. These rely on water for cooling in the power generation process

'Low rainfall' 20-40% less than normal. 'Very low rainfall' more than 40% less than normal.

Rivers/ Lakes The River Danube in Serbia fell to its lowest level in 100 years. This allowed World War 2 bombs and tanks to be revealed for the first time. These caused a danger to people swimming in the rivers. Reservoirs and rivers used for public water supply and hydroelectric schemes either dried up or ran low.

Glaciers 10% of the Alpine glacial mass melted Glaciers were melting rapidly and swelling rivers and lakes to dangerously high levels. Matterhorn 4478 m

Fires Terra Daily LISBON (AFP) Aug 22, 2003 This was the largest area of Portugal hit by forest fires Forest fires destroyed at least 330,000 hectares in Portugal, new record.

Thirty-two thousand fatalities makes it an enormous natural disaster." According to Janet Larsen of the Earth Policy Institute (EPI), 35,000 Deaths in five nations Health

nuclear plant shutdowns It is thought that one third of the deaths caused by the heatwave in the UK were caused by poor air quality. Pollution

Tourism At Bournemouth, in Dorset, the coastline was crammed with about 100,000 sun lovers, and there was said to be no spare space on the sand. Britain has recorded its hottest day ever as the temperature soared to 38.1C (100.6F) in Gravesend, Kent.

Transport Roads to the south and west were jammed as motorists headed out of the sweltering cities Speed restrictions to prevent buckled rails have been in force on the railways from noon each day while temperatures continue above 30C.

Drought: Wheat crops failed by 10% for the whole of Europe. Farming Grape: The heat wave greatly accelerated the ripening of grapes.

Immediate responses to the heatwave France requested aid from the European Union to deal with the effects. Public water supply shortages occurred in several countries, including the UK and Croatia, which led to a temporary ban on using hose pipes. TV news, internet and newspapers informed the public on how to cope with the heat - drinking plenty of water, wearing cool clothing, and staying in the shade in the middle of the day. Network Rail in the UK imposed speed restrictions for trains when the temperature was above 30 °C. This was to help avoid trains derailing when railway lines might have buckled Workers around Europe altered their working hours. Some refuse collectors started earlier to pick up rapidly decomposing rubbish from the streets.

As a result of the European heatwave: A joint Met Office/Department of Health project called the Heat-Health Watch now gives advanced warning of UK hot. weather. It operates every summer from 1 June to 15 September. The French government has made efforts to improve its prevention, surveillance and alert system for people such as the elderly living alone.

Hazard? Explain how anti-cyclones may lead to hazardous conditions