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Theme C: Weather & Climate by

Measuring the Elements of the Weather

 

Weather & Climate

Weather is defined as the day to day changes in the conditions of the atmosp­here some examples of this include cold, dry, windy.
However climate is defined as the average weather conditions of an area taken over a period of 35 years. Climate can be temperate, tropical, equato­rical or polar/­arctic.

Recording the Weather

Ther­mom­eter
A thermo­meter measures temper­ature in degrees celcius.
Tradit­ional thermo­meters contained mercury which expanded with the rising temper­ature. It was later replaced with alcohol and red/blue dye.
Now we use digital thermo­meters with electric resistors (therm­istor) which are temper­ature sensitive. As the thermo­meter becomes more conduc­tive, microc­omputer finds the temper­ature by measuring the conduc­tivity displayed.
Anem­ome­ter
An anemometer measures wind speed in kph, km/h or knots.
It consists of a set of 4 plastic cups mounted at the end of bars on a pole, the cups are attached to a meter below centre. One cup is coloured red to show the movement of wind, meter records the speed of wind.
Rain Gauge
A rain gauge measures precip­itation in mm.
A metal cylinder containing a collecting bottle and funnel, stabilised to prevent a tilt from wind. At specific times the water is emptied into a specially calibrated measuring cylinder and measured in millim­etres.
Wind Vane
A wind vane measures the wind direction using the compass points.
Consists of a metal pole about 2m off ground or on top of a building, two bars cross at right angles. Main points of the compass are indicated on 4 ends, set facing north and spins when wind blows.
Baro­meter
A barometer measures air pressure in milibars.
Atmosp­heric pressure is the weight of air pressing down on us. Air is light but because there is so much of it above us, it exerts a pressure on us. Atmosp­heric pressure is measured by a barometer. The units used are millibars. The greater the reading, the higher the pressure. Normal pressure is 1000mb with a reading above this being regarded as high pressure and a reading below is regarded as low pressure.
Stev­enson Screen
Records humity and temper­ature.

Clouds

Clouds

Stratus: These are layered clouds that are low, grey and shapeless and usually are like a blanket of cloud over an area. They can bring some drizzle and rain.
Cumulus: These are clouds that move quite quickly. They are white and fluffy and look like cotton wool. They can bring rain showers – especially when the base is grey.
Cumulo­nimbus: These are much deeper clouds that climb high into the atmosp­here. They often contain a lot of heavy rain and are associated with thunder and lightning storms.
Cirrus: These are very high clouds that are wispy and made up from ice crystals.

Weather Foreca­sting

A weather forecast is made using computers and records of past weather patterns to predict current weather
1. Land based weather station
2. Weather balloons
3. Weather buoys
4. Weather ships
5. Satellites (Geost­ati­onary and Polar)
 

Factors Affecting Climate

Lati­tude
Affects relative position of sun in the sky. Places near or at equator are warmer than poles as they get stronger more direct radiation from sun. Radiation travels through less atmosp­here, reduced chance of being reflected back by particles or clouds.
Alti­tude
Upland areas tend to be wetter than lowland places as air is forced over mountains, cools and water vapour condenses to create clouds and rain. Temper­atures falls as height above sea level increases (1 degree per 100m).
Prev­ailing Winds
Bring different amounts of moisture and heat depending on where they have come from. Places with prevailing winds from dry, hot, contin­ental interiors usually have a desert climate eg. Atacama, South Africa. The prevailing wind for the UK is South-­Wes­ternly
Distance from Sea
(Conti­nen­tially) influences the temper­ature range. Areas close to the sea tend to have a lower temper­ature range than inland. This is because the sea is a liquid and heats up less quickly than land. However it holds heat for longer. In winter months, warmed sea around coastal areas spreads heat to nearby land meaning they are warmer than inland areas.

Air Masses

Air Masses

Airmass
Direction
Moisture Charac­ter­istics
Temp. & Seasonal Variation
Polar Maritime (PM)
N-W
Wet
Cold & wet (Winter) Cool & damp (Summer)
Tropical Maritime (TM)
S-W
Wet
Mild & wet (Winter) Warm & rainy (Summer)
Polar Contin­ental (PC)
N-E
Dry
Cold & dry (Winter) Hot & dry (Summer)
Tropical Contin­ental (TC)
S-E
Dry
Mild & dry (Winter) Hot & dry (Summer)

Synoptic Charts

Synoptic Charts

Synoptic charts are maps which summarise the current weather condit­ions. They record the weather using a set of symbols. They show the fronts of a depression and the variation in pressure of the air using isobars.
 

Weather Systems & Extreme Weather

 

Depres­sions

Depres­sions are low pressure systems. They usually approach from the West and move East. Winds in a depression blow anticl­ockwise and into the centre of low pressure. When air gets into the centre of the low pressure it rises. Depres­sions can be 100s of kms wide. Depres­sions have 2 fronts called the warm front and the cold front. In between these 2 fronts is an area called the warm sector. The circular lines around a depression that show air pressure are called isobars and show air pressure measured in milibars.
 
 
Warm Front
Warm Sector
Cold Front
 
Cirrus - High in sky. Thickens
Low Stratus
Cumulo­nimbus (high), isolated cummulus
 
No rain yet.
Mainly dry
Heavy rain
 
High but decreases
Lowest
Rising
 
Strong
Increases
North Westerly

Depression Cross-­Section

Warm Front
Cold Front
Occluded Front
Warm (TM) air is pushed eastwards and is forced to rise gently over the colder denser (PM). As it rises it cools and condenses to form a band of steady rain which arrives before the warm air is felt.
Cold dense air is pushing hard into the warm air, it causes this warm lighter air to rise, causing tall clouds and heavy rain.
As a depression begins to die the cold front catches up with the warm front and lifts the warm airmass off the ground. This is called the occluded front. If this front passes over you will not notice any change in temper­ature at ground level as it remains cold but you will have a band of very heavy rain.

Anti-C­yclones /

Anticy­clones are high pressure systems. In the centre the air sinks and rotates slowly clockwise. There is little chance of clouds or rain in an anticy­clone because sinking air compressed warms up near the ground. Air can hold more vapour, no conden­sation, no clouds. No clouds, no rain. On a weather map the isobars for an anticy­clone are spaced well apart and this means winds are calm/g­entle. Unlike a depression an anticy­clone has no fronts because there is only 1 air mass. Fronts only occur where there are 2 airmasses. An anticy­clone moves very slowly.
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Summer Anticy­clone
Winter Anticy­clone
- Cloudless skies
- Fog & mist
- High temper­atures
- Form at night
- Sunshine
- Cold

Case Study: Typhoon Haiyan 2013

Typhoons are tropical storms created from low pressure systems in tropical areas. They are also known as hurricanes or cyclones. Distinct structure with spiralling cloud and a central eye that can be seen from space.
The Philip­pines is vulnerable to typhoons as large amounts of warm water surrounds the 7000 islands. Evapor­ation followed by conden­sation releases large energy amounts as latent heat. Few pieces of land to slow typhoon down, meaning powerful storms.
Back­gro­und
Most powerful hurricane to hit area. Locally called Typhoon Yolanda and made landfall on 8th November 2013. Category 5 hurricane that brought sustained winds of 23km/h and gusts of 280/h. Days before landfall carefully watched by joint typhoon warning centre (JTWC) and PAGASTA using satellites and local weather station data. Haiyan tracked through Philip­pines in only 24 hours. Caused a storm surge of 8m in some areas.
Impacts on People
- 6190 dead, 1785 missing
- 371,000 evacuated and many more in refugee centres that were destroyed.
- Further loss of life caused by cholera and dysentery due to decaying corpses and raw sewage contam­inating water supply.
- Millions experi­enced disruption to electr­icity supply, Bogo without power for weeks.
Impacts on Property
- 5mil saw homes severely damaged or destroyed. 90% of structures wiped out across 500mile radius of eye.
- 10,390 schools destroyed
- Newly built civic buildings destroyed. Including new Bogo city hall which was opened in April 2013 - it was destroyed when the roof was ripped off it.
- Many sought refuge in indoor stadium with reinforced yet died when it flooded.
- Airport was severely damaged, terminal destroyed by 5.2m surge. Runway was submerged.
Impacts on Enviro­ment
- 71,000 acres of farmland destroyed
- Thousands of trees uprooted, massive release of carbon dioxide. Habitats destroyed and roads blocked.
- Flooding impacted enviro­ment, power barge. 103 knocked over, oilspill would later affect mangrove ecosys­tems.

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