Storm SurgersStorm Surgers

Weather – The BasicsWeather – The BasicsDepressionsDepressions Low pressure systems (often below 1000mb)Low pressure systems (often below 1000mb) Represented on weather map with closed isobars and Represented on weather map with closed isobars and

decreasingdecreasing pressure towards the centre pressure towards the centre Move across the UK from west to eastMove across the UK from west to east Isobars are close together, indicating a steep pressure Isobars are close together, indicating a steep pressure

gradient. This can cause strong windsgradient. This can cause strong winds

Weather – The BasicsWeather – The BasicsAnticyclonesAnticyclones High pressure systemsHigh pressure systems Closed isobars with pressure Closed isobars with pressure increasingincreasing towards the towards the

centrecentre They move slowly and can remain stationary for They move slowly and can remain stationary for

days/weeksdays/weeks Isobars are far apart so there is little pressure difference Isobars are far apart so there is little pressure difference

(light/no winds).(light/no winds).

Storms – The BasicsStorms – The Basics Air covers the surface of our planet and has mass, that Air covers the surface of our planet and has mass, that

is, it has weight and volume, and it can be made to is, it has weight and volume, and it can be made to move.move.

Our atmosphere is dynamic, and it's temperature Our atmosphere is dynamic, and it's temperature constantly changes in response to rotation of the planet, constantly changes in response to rotation of the planet, changes in seasons and earth's orbit around the sun. changes in seasons and earth's orbit around the sun.

Hot air is less dense than cold air, and when hot and Hot air is less dense than cold air, and when hot and cold air collide, the hot air is forced to rise over the cold air collide, the hot air is forced to rise over the colder air. colder air.

Cold air is typically dryer than warm air and originates Cold air is typically dryer than warm air and originates from the poles. Warm air comes from the tropics/equator from the poles. Warm air comes from the tropics/equator (where there is more evaporation). (where there is more evaporation).

Storms – The BasicsStorms – The Basics Whenever cold dry air moves away from the poles, it eventually Whenever cold dry air moves away from the poles, it eventually

encounters warm wet air moving away from the equator. encounters warm wet air moving away from the equator. The warm wet air is forced up and over the cold air. When the The warm wet air is forced up and over the cold air. When the

warm air is forced up, it causes surface air pressure to drop.warm air is forced up, it causes surface air pressure to drop. Cold air rushes in to fill the area of lower air pressure, which Cold air rushes in to fill the area of lower air pressure, which

causes more warm air to be displaced upward, and more cold causes more warm air to be displaced upward, and more cold air moves in, forcing more warm air upward, and a cycle starts air moves in, forcing more warm air upward, and a cycle starts to develop. to develop.

Also, factor-in that the earth rotates from west to east, dragging Also, factor-in that the earth rotates from west to east, dragging the atmosphere with it. The low-pressure area starts to rotate, the atmosphere with it. The low-pressure area starts to rotate, and all this moving air creates wind, and lots of it. and all this moving air creates wind, and lots of it.

So a storm forms in response to an extreme difference in air So a storm forms in response to an extreme difference in air pressure, driven by the movement of cold and warm air. pressure, driven by the movement of cold and warm air.

Eventually either the cold or warm air dissipates, and Eventually either the cold or warm air dissipates, and equilibrium becomes re-established and calm, less-windy equilibrium becomes re-established and calm, less-windy weather prevails. weather prevails.

A storm can last as short as a few days to over a week.A storm can last as short as a few days to over a week.

Storms – The BasicsStorms – The Basics The greater the difference in air pressure between two The greater the difference in air pressure between two

competing systems, the greater the wind. competing systems, the greater the wind. The greater the surface area covered by low pressure, The greater the surface area covered by low pressure,

the greater the size of the area of wind will be. the greater the size of the area of wind will be. The deeper or lower the pressure, the stronger the The deeper or lower the pressure, the stronger the

storm, the stronger the wind, and the greater the storm, the stronger the wind, and the greater the probability for surf to be generated. probability for surf to be generated.

The larger the area of low pressure, the larger the fetch The larger the area of low pressure, the larger the fetch or ocean surface that will be affected by the resulting or ocean surface that will be affected by the resulting wind. wind.

Storm SurgesStorm Surges Strom surges occur when weather conditions create Strom surges occur when weather conditions create

strong winds (large fetch), which in turn produce higher strong winds (large fetch), which in turn produce higher water levels than you would normally get at high tide water levels than you would normally get at high tide (basically the wind blowing across the surface off the sea (basically the wind blowing across the surface off the sea causes water to pile up to a level higher than normal).causes water to pile up to a level higher than normal).

The North Sea and The Bay of Bengal are two areas The North Sea and The Bay of Bengal are two areas where these conditions can occur because they are both where these conditions can occur because they are both narrow areas of sea.narrow areas of sea.

Strong winds drive waves ahead of the storm, which Strong winds drive waves ahead of the storm, which builds up the water levels in areas where there is a builds up the water levels in areas where there is a limited space for the water to go.limited space for the water to go.

North Sea Storm Surge (1953)North Sea Storm Surge (1953)CausesCauses Deep Atlantic depression (low pressure) came over Deep Atlantic depression (low pressure) came over

Scotland and continued to worsen. Strong gales (32-42 Scotland and continued to worsen. Strong gales (32-42 knots). Pressure of 970mbs.knots). Pressure of 970mbs.

A rapid fall in pressure could be responsible for a rise in A rapid fall in pressure could be responsible for a rise in the surface of the sea of about 0.5mthe surface of the sea of about 0.5m

An anticyclone (high pressure) lay west of Britain. The An anticyclone (high pressure) lay west of Britain. The steep pressure gradient (difference between low and steep pressure gradient (difference between low and high pressure system) caused strong winds to move high pressure system) caused strong winds to move south across the North Sea. (The anti-clockwise south across the North Sea. (The anti-clockwise movement of the low system sucked down air from the movement of the low system sucked down air from the North, which created these gales).North, which created these gales).

Large fetch from the North. Storm waves over 6m highLarge fetch from the North. Storm waves over 6m high All at the same time as high spring tides and rivers All at the same time as high spring tides and rivers

discharging into the sea with large volume of water (due discharging into the sea with large volume of water (due to floods)to floods)

North Sea Storm Surge (1953)North Sea Storm Surge (1953)EffectsEffects Lots of extra water in the North Sea.Lots of extra water in the North Sea. Sea defences breached in south east England and the Sea defences breached in south east England and the

NetherlandsNetherlands Thousands of hectares of low-lying land floodedThousands of hectares of low-lying land flooded Damage to property, communication systems and farm landDamage to property, communication systems and farm land 250 people drowned in England compared to 1800 in the 250 people drowned in England compared to 1800 in the

Netherlands.Netherlands. More damage in the Netherlands. More damage in the Netherlands. Both countries responded with coastal management Both countries responded with coastal management

schemes.schemes. Countries affected included the UK, Netherlands, Belgium, Countries affected included the UK, Netherlands, Belgium,

Denmark & France.Denmark & France.

Storm Surges in BangladeshStorm Surges in Bangladesh Events in 1970, 1985 & 1991.Events in 1970, 1985 & 1991.

CausesCauses High winds (due to a cyclone forming to the south) pushed High winds (due to a cyclone forming to the south) pushed

water northwards.water northwards. The Bay of Bengal is narrow, so struggled to contain the The Bay of Bengal is narrow, so struggled to contain the

extra water.extra water.

Causes of CyclonesCauses of Cyclones Low pressure systems that develop in the tropics.Low pressure systems that develop in the tropics. Surface heating causes warm air to be drawn into it in a Surface heating causes warm air to be drawn into it in a

spiralling manner.spiralling manner. The sea needs to be over 27`C = maintain rising currentsThe sea needs to be over 27`C = maintain rising currents

Storm Surges in BangladeshStorm Surges in BangladeshEffectsEffects 10m waves hit densely populated coastline.10m waves hit densely populated coastline. Storm surge travelled several km inland destroying Storm surge travelled several km inland destroying

everything (poorly constructed buildings so easily swept everything (poorly constructed buildings so easily swept away).away).

Densely populated so 300,000 deaths in 1970.Densely populated so 300,000 deaths in 1970. Salt water contaminates soil – country relies on agriculture – Salt water contaminates soil – country relies on agriculture –

subsistence life style. Leaves many dependent on aidsubsistence life style. Leaves many dependent on aid

ResponsesResponses Attempts to protect areas with embankments and mangrove Attempts to protect areas with embankments and mangrove

plantations to act as buffers. Some success, but little money plantations to act as buffers. Some success, but little money for large scale management schemes.for large scale management schemes.

Problem will only worsen with global warmingProblem will only worsen with global warming

Sediment CellsSediment Cells Coastal sediment comes from a variety of places: sea Coastal sediment comes from a variety of places: sea

bed, beaches, cliffs, river channels and estuaries.bed, beaches, cliffs, river channels and estuaries. Some believe that sediment movement occur in distinct Some believe that sediment movement occur in distinct

areas (or cells). These are closed systems with balanced areas (or cells). These are closed systems with balanced inputs and outputs.inputs and outputs.

There are 11 cells in England and Wales. There are 11 cells in England and Wales. http://jncc.defra.gov.uk/pdf/gcrdb/v28chap1.pdf

They are separated by headlands or stretches of deep They are separated by headlands or stretches of deep water.water.

In reality, sediment could easily move cells e.g. around a In reality, sediment could easily move cells e.g. around a headland.headland.

UK sediment cellsUK sediment cells

High & Low Energy CoastlinesHigh & Low Energy CoastlinesHigh EnergyHigh Energy Wave power is strong for Wave power is strong for

most of the year e.g. west most of the year e.g. west coast of British Isles. The coast of British Isles. The prevailing wind is westerly prevailing wind is westerly and they face the direction of and they face the direction of the longest fetch.the longest fetch.

Distribution of these Distribution of these coastlines is controlled by coastlines is controlled by climate and the direction they climate and the direction they face.face.

Strong winds are more Strong winds are more frequent in areas where there frequent in areas where there is a cool temperate western is a cool temperate western maritime climatemaritime climate

High wavesHigh waves

Low EnergyLow Energy These can be found when These can be found when

the coastline changes the coastline changes direction and when there are direction and when there are few strong winds.few strong winds.

Estuaries, inlets and Estuaries, inlets and sheltered bays occur where sheltered bays occur where wave heights are lower.wave heights are lower.

Waves spread outwards and Waves spread outwards and energy is dissipated leading energy is dissipated leading to depositionto deposition

Enclosed sea areas also Enclosed sea areas also have low energy e.g. Baltic have low energy e.g. Baltic SeaSea