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OCEAN CURRENTS – CORIOLIS EFFECT - WATER TYPES- MONSOONS –

FOG & MIST- EL NINO – LA NINA – THUNDER & LIGHTNING.

Approximately ¾ of the earth’s surface is covered by water of varying depths. This results in great influence on the

weather in conjunction with the sun. 97% of the water is saline. The 3% which is fresh water is mainly stored in the

Polar, Antarctic & Greenland Ice sheets and the mountain glaciers. There is only about 1% of fresh water easily available

because a proportion of the remainder is ground water.

OCEAN SALINITY Vis Aid 71 & 72

The sea stores and releases heat in a slow and measured fashion under the influence of the sun like a colossal radiator,

according to the seasons. In fact the top 10 ft. of the ocean’s surface holds more heat than the whole of the earth’s

atmosphere. The U.K in particular bathes in a generous helping of this warmth thanks to the Gulf Stream, which gives us

the heat equivalent to about a million power stations.

This variation in heat loss or gain affects the world wide movements of both sea and air currents.

Water provides the moisture for the maintenance of all life on earth and, like air, without it we would never have a

Planet Earth as we have today. It is also necessary for the cloud formations, which in turn greatly affect the weather

systems. They are greatly affected by the rotation of the earth which is responsible for the movement of the great sea

masses or currents. They are also driven by temperature variations of the water in different areas of the world and also

by the winds.

These currents, like the winds, when found initially by the explorers, were kept a secret as it gave them the advantage in

speed, developing trade routes and discovering new lands.

The Spanish & Portuguese were really the first, followed by the British and the Dutch, to find and use the ocean

currents to their advantage. There are also legendary tales about the Vikings and also Irish Monks finding their way

across the great oceans to find new lands. Recently, though, there has been some research about the Vikings that lends

some belief to the legends.

The ocean currents have been likened to a world central heating /air conditioning system. The currents move around

the Northern Hemisphere in clockwise loops and anticlockwise loops in the Southern hemisphere, aided by the winds and

transferring heat as they go. Just to make things a touch more difficult, there is a further aspect to the way these

currents operate. Our old friend, the Coriolis Effect, affects the winds, which assist in the movement of the currents

and to some degree affects the currents.

Coriolis Effect Vis Aid 48

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In 1955 a young English scientist in the National Institute of Oceanography designed a buoy that could float in the

sea at various & fixed depths and go with the currents. This buoy led to the invention of modern robotic buoys called

Argo. There are more than 3600 free drifting profiling buoys measuring the temperature, salinity and velocity of the

upper 2000 m of the oceans. They dive up & down automatically in the oceans relaying back via GPS system satellites the

relevant information to Weather Depts., Govt. Depts., Universities and other organisations which co-operate in

developing info about the seas & weather. With a life of approx. 18 months, they send information about the powerful

currents in the ocean’s depths, knowledge that wasn’t as available prior to the invention of the buoys. These 3600 buoys,

strung around the world from the Arctic to the Antarctic, are all adding to the data bases which improve weather

forecasting and our knowledge of the global climate. Currently, sea level is rising at about 3 mm per annum, Arctic sea ice

cover is shrinking and high latitude areas are warming, with some melting of Ice Packs.

Due to the earth's rotation the winds blow at an angle to the parallels of longitude. In the northern hemisphere, air

moving North is deflected to the East and if it is moving south, to the West. Normally you would expect warm water to

go straight towards cold water to even the temperature. However, due to the Coriolis Effect on the winds, these have an

effect together with the earth's rotation on the currents. As a result, some have a circular tendency.

Ocean Currents VA 73

There are over at least 14 major ocean currents, including the Agulhas, the Benguela, the Humboldt, the Guroshio

(Japan), the Gulf Stream, Labrador current, California current, Canaries current, E. Australia current, Equatorial

current, N. Atlantic, N. Pacific drift, Kamchatka current and the West Wind drift.

The Gulf Stream is well known in the UK and thank God for it otherwise we should have a much colder climate than we

have. It is one of the world's strongest currents. Here's how it works.

The warm waters of the Caribbean & the Gulf of Mexico moves northward into the North Atlantic, head towards

Western Europe, gradually losing heat and sinking, pushing its way into the semi Polar Regions. The Gulf Stream here

brings an increase of about 9oC to the region, much more than average temps for similar latitudes without proximity to

the sea. The water in these regions meanwhile is becoming even colder, due to the effect of the Polar land mass and

temperature, and sinking itself displaces water to the south which heads towards the Equator. The returning stream

brings cooler summers to the coastal regions of Spain & Morocco. Circular activity takes place and these strong ocean

currents with their attendant air streams move towards the Caribbean Sea. These warm easterly winds are known as the

Trade Winds.

Sometimes the main currents have a terrific effect on the adjacent land mass. It's no accident that much of the

western side of the southern part of Africa is desert. The Benguela current, a cold current from the Polar region, flows

north along the western side of South Africa, past Angola, Namibia, and Botswana, all of which are desert countries with

the Kalahari & Namibian deserts. The Humboldt cold current flows North alongside Western South America, Chile and

Argentina with the Atacama and Patagonian deserts. The ENSO also has an effect here and to some degree the world

over. We’ll come to that in due course. On the eastern side of Africa, the Algulhas warm current, a strong swift flowing

current does not have the same effect, although there are apparently problems for shipping due to rogue waves.

WATERCYCLE V.A. 74/75/76

Although 3/4 of the earth's surface is covered by water, as we have discussed, most of it is salt water, which can cause

problems to life. From the weather viewpoint this doesn't really matter, because water circulates due to the effect of

sun and wind. Water exists in 3 states :- VAPOUR, LIQUID and SOLID.

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Vapour state makes the cloud, water state makes the rain and solid state makes the ice or snow or hail. There is also a

mixture of solid & liquid which we call sleet. When you get a mixture of any or all of these types plus wind plus

temperature rise and fall, that’s when you have weather, and it can be good or bad. Too much of any of these conditions

can be disastrous.

Let’s have a look at this circulation and how the water goes from and returns to the earth.

Evaporation

This is the process of a substance in a liquid state changing to gaseous because of increased temperature or pressure. It

is part of the water cycle.

Condensation

This is the process of state change from gaseous to liquid state due to lowering of temperature or pressure

Precipitation

The action of rain, snow, sleet or hail falling to the ground from clouds

Transpiration

This is the process whereby plants absorb water through their roots and give it out as vapour through their leaves.

Infiltration.

This process is the action of absorption of liquid by the ground surface due to gravity & capillary action. If precipitation

exceeds infiltration, run off and possibly flooding may occur.

RELATIVE HUMIDITY V.A. 77

Besides rain, the water in the air has another effect on us. If the air around us is warm & full of water vapour it is said

to be humid and makes us all feel uncomfortable, and high humidity is said to exist. Why?

It is due to the high amount of water vapour in any given mass of air. This condition is important also from a forecasting

viewpoint and it is known as Relative humidity. This is the measure of water vapour in a specific volume of air compared

to the maximum amount that the air could hold at that temperature. This makes a difference to us from a comfort

viewpoint. Tropical rain forest can sometimes almost reach 100% R.H which is extremely uncomfortable.

MONSOONS. Vis Aid 79

The monsoon most people know of is the Indian summer monsoon, although we apparently sometimes get one in the UK

usually around Glastonbury festival time! The word is based on an Arabic word for season and marks a switch from cold

winter weather to warm summer weather. On the Indian sub-continent, the winter winds blow cold from the centre of

the continental Asian mass. In summer, the winds are reversed and blow north from the warm Indian Ocean. There is

usually a period of extreme heat over India and S. E. Asia in early summer and then comes the clash of the cold dry

winds and the warm wet winds. It is usually welcomed as it brings considerable rainfall and flooding and relief from the

heat. Although vital to the harvest not to mention the comfort of the inhabitants it sometimes causes catastrophic

flooding and tremendous loss of life and incredible hardships to the local inhabitants.

FOG & MIST Fog 81, Mist 82 & Dew Point 80

As we have discussed, as air cools it can’t hold as much water vapour as when it is warm. Eventually the water vapour will

condense, especially in industrial areas and form droplets. The temperature at which vapour in air condenses is known as

the DEW POINT. Condensation is easily seen after a warm day when there is no cloud and the night is clear. The air

radiates heat away from the ground and many surfaces, and becomes cold with the result that water droplets (dew)

forms on them. This situation can also give rise in winter, spring and autumn to the formation of fog or mist. The

temperature drop will determine which it is.

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In the UK fog is defined as a situation in which visibility is 200 m. or less. For aviation purposes it is 1000m. When it

falls below 50m it is very hazardous. Otherwise, restricted natural visibility above 200m is called mist.

There several types of fog.

RADIATION FOG This usually occurs on still, clear night. The air cools and condensation occurs. The resulting fog is

often patchy but may increase in density and area coverage as night wears on and the temperature falls further.

ADVECTION FOG

This occurs when warm damp air moves into a cold area and the lower layers of the air cool down to the dew point. This

often happens in early spring when the ground is snow covered or still very cold. The sun will usually move mist or fog if it

can lift the temperature sufficiently to enable air to hold water as moisture. A wind stronger of about 5 - 10 knots will

usually move both Mist & Fog.

However, in valleys and low-lying enclosed areas these phenomena can stay for some time especially in winter in calm

conditions.

HILL FOG

This occurs when air is forced up a slope or mountain. The air cools down and if it doesn’t reach the hill tops it becomes

fog

COASTAL FOG occurs when moist air is moved over a cooler sea. It often occurs in Spring & Summer very often in the

S.W. & North Sea coasts. It is sometimes known as HAAR in some parts of the U.K. coastal areas and FRET in others.

STEAM FOG

This often occurs after a shower when the earth’s surface is warm and the rain evaporates. If the air above it is

saturated then the excess moisture condenses and looks like steam.

SMOG

We have all experienced the dreadful effect of industrial smoke or haze in conjunction with fog. It is a killer in some

places. It is a mixture of smoke, vehicle and industrial emissions in the air, and in some climates or cities e.g. San

Francisco or Athens there is often a chemical reaction with sunlight. It is harmful to health, has a slightly corrosive

effect on materials and humans and generally is not very nice.

FROST occurs when cold damp air settles on a colder surface, the temperature at the surface falls to 0oC or below and

the moisture in the air turns to ice. If the air is very dry frost will not occur irrespective of the surface temperature.

The Surface Temperature referred to by Met Men incidentally is actually 1.5 m. above the surface. This is because air

temperatures can and do vary at different levels.

There are different types of frost.

AIR FROST

This happens when the air is colder than that in contact with the ground, which may have some warmth remaining. This

can happen in autumn.

HOAR FROST V.A. 88 & 89

This is a layer of fluffy ice crystals, caused by moisture which freezes instantly on ice-cold surfaces. If there is a wind

about it won't happen.

RIME FROST.

This needs a very low temperature to form and as soon as the moist air hits a surface (on the windward side) it forms

sometimes in extraordinary shapes. The vapour in the air is normally supercooled. This occurs when there is no dust or

minute solid on which the water vapour can materialise into moisture. The temperature can drop as low as – 48oC

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FERN FROST

Those of us who are old enough to remember sleeping in bedrooms without central heating in the winter will no doubt

remember the beautiful patterns that used to occur on the inside of the bedroom window on a frosty night. It starts

when DEW forms on the cold glass than freezes as more air hits the window, more ice crystals form and leaf-like

patterns start to form

Sometimes you may hear the term 'Inversion'. We discussed this when we were talking about the sun Vis Aid 69.

An inversion occurs when any layer of air is warmer than the layer beneath it.

PACIFIC NORMAL Vis Aid 83

In the middle part of the 20th Century two strange weather phenomena began to be recognised. It has been said that,

next to the seasons, they are the largest causes of weather /climate variability on the Earth. They can cause extremely

severe weather problems throughout most of the world. They are

El NINO & LA NINA

An El Nino event in 1997/8 caused over 2000 deaths and a global damage bill of over £19 billion. The recent El Nino in

2015 caused considerable damage and we are beginning to experience some effects of the present La Nina. Much more

has been learnt about them since the 60’s and they are the subject of considerable study by meteorologists. Apparently

some archaeological evidence has been found that they have been occurring for at least 15000 years.

EL NINO

The western Pacific is normally about 5o-10oC warmer than the Eastern Pacific. In El Nino years the water increases in

temperature in the Western Pacific causing a strange up welling of warm water and a westerly current carries it to the

western coast of South America interfering with the nutrient rich cold northerly currents, which normally flow north

along the coasts of Peru and Ecuador. It occurs on average about every 5 years, but can appear as frequently as every

three years or as little as every seven years. Its strength varies considerably as obviously do the effects. It usually

starts around during the Christmas season, which is why it has been called El Nino, the boy child. The technical term for

it is E.N.S.O ; El Nino southern oscillation.

NORMAL v EL NINO Vis Aid 84

If normal easterly winds in the Pacific weaken and westerlies appear, the effects on weather conditions can be

considerable over much of the Earth’s surface. Droughts in Southern Africa, S.E. Asia, India and Australia, droughts or

floods over parts of the United States and even some weather effects over Europe also happen. Generally Europe gets a

wetter, colder summer than normal, although Southern Europe may get a drier and hotter summer. Considerable action

has been taken to allow meteorological offices around the world to learn when El Nino is starting although at present

there is still much to learn about its causes.

LA NINA VisAid 85

This is another weather phenomenon, which occurs in the Pacific Ocean and has an opposite effect to El Nino. It usually

but not always happens in the first or second year after an El Nino event. Extensive cooling of the ocean on the eastern

and central areas usually leads to increased temperatures on the western side. The resulting effects of La Nina means

increased rainfall in N & N.E Australia, S. Africa, Central America, China, Indonesia & Papua New Guinea. An increased

monsoon usually occurs in Southern Asia. Overall wet areas will experience more rainfall and dry areas such as Central E.

Africa, SW USA, N Mexico and the normally drier areas of S. America will get less rainfall. Atlantic and Pacific

hurricane and cyclone activity also increases.

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La Nina generally lasts for about 10-12 months at a time, subject to the Jet stream behaving itself. Its effect on the

U.K. varies but a strong La Nina can greatly affect our summers

THUNDER & LIGHTNING. Vis Aid 86

Thunderstorms exist in Cumulonimbus clouds; huge, towering dark threatening clouds caused by extremely rapid ascents

of warm moist air that can reaches heights from up to 3 miles to 12 miles in the Tropics and ice crystals take the place

of moisture in the air. The top of the cloud characteristically has an anvil shape apparently caused when the cloud top

hits the Tropopause. To add to the fun the rapidly ascending air currents are matched by rapidly descending very cold

downdraughts. The ice crystals within the clouds obviously collide and apparently this causes charges of electricity. The

size of the clouds and the turbulence within it generally means that there is a build – up of positive and negative electric

charges building up at the top and bottom of the cloud. The negative charges tend to sink to the lower parts of the cloud

and as the ground is positively charged, the result is an electrical discharge to objects on the nearest ground such as

Lightning conductors. This discharge also happens with the cloud itself. Lightning can generate heat around 25000o C

BALL, SHEET & FORKED LIGHTNING

A small moving ball of light. The cause is as yet unknown but there are weird tales of it moving through pilot's control

areas, frizzing up people's hair, moving through houses etc. It can carry a considerable distance (miles) from its source.

SHEET LIGHTNING

This usually occurs when there is discharge between clouds. A fairly common occurrence, it usually appears as a blinding

flash of light that illuminates the sky, and is caused by electrical discharges between and within clouds.

FORKED LIGHTNING

This is probably the most common as it usually discharges from cloud to ground. More often than not, it has a jagged

path to the ground due to the electric charge taking the easiest path to the ground. The bright flash seen is really the

return flash from ground to cloud. Lightning is dangerous so take precautions when there is lightning walking about! E.g.

don’t play Golf or stand under an isolated tree or go for a walk if you have metallic fillings or hobnailed boots on!

ST. ELMO’S FIRE Vis Aid 87

St. Elmo also known as St. Erasmus. He was martyred in A.D. 303 after considerable torture and is supposed to be the

patron saint of sailors, sufferers from intestinal troubles and labour pains. The sailors thought that the discharges at

the mastheads of ships etc. were proof that he was protecting them.

It isn't fire but a greenish or white light that seems to hover or be attached to elevated objects such as ship's masts,

aircraft wing tips, weather vanes or lightning conductors. It happens when electrical storms are near. The normal name

for it is brush discharge.

THUNDER

Compared to lightning, thunder is a pussycat. It is caused by the lightning discharge generating enormous heat and

therefore expanding the air masses extremely rapidly. The result is boom and bust as the air cools down again

immediately and results in tremendous noise. The Portuguese explorers when passing West Africa where electrical

storms are extremely common named one country Sierra Leone (Mountains of the Lion) because of the almost continuous

thunder at night. Lots of people are frightened by thunder although it does very little damage, except perhaps to the

ear drums. There’s the story about the little boy who was crying in the night and when his mother went to comfort him

he told her he was afraid of the Thunder and asked her if she would stay in his bed with him. She told him she couldn’t

really, the noise wouldn’t hurt him and he had to be a big brave boy. And also she had to sleep in Daddy’s bed. The little

boy got very upset at this and said to her ‘Well you tell him he’s a great big coward’.

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Finally if you want to work out how far away the thunderstorm is count the seconds between the Lightning flash and the

Thunder and divide by five. The answer is the distance the storm is from you in miles. An approximation of course.

Well, that’s all the sessions on Earth, Air, Fire & Water. The next sessions will be on Clouds.

Weather Forecasting and brief details on the history of the development of this extremely important science has been

covered. I hope you have found it interesting! If you like, we can have a session dealing with your questions, comments

and a general discussion on the various aspects of meteorology for a final meet on 3rd November.

Ref Water