Weather & Weather & ClimateClimate

Weather and Climate Weather is the state of the

atmosphere at any one place or time. This includes: humidity, temperature, sunshine hours, cloud cover, precipitation (any moisture reaching the earth’s surface). This includes rain, sleet, snow, hail, dew and frost.

Song:

http://www.youtube.com/watch?v=c3MKsTLnTKc

Climate is the average or long term weather conditions of a region. It is the result of years of research into data.

Weather or Climate

Hot and dry conditions, together with strong winds, led to Bushfires near Wagga.

At this time of year Darwin usually experiences hot and wet weather.

The maximum temperature in Moscow today is -23oC

On Monday night a southerly change arrived about 10:30pm

Climate Weather

Weather or Climate

Tully in Queensland is Australia’s wettest town.

September was chosen for the 2000 Olympics because that month usually has the best weather.

On New Year’s Day the temperature in Sydney was 45oC

Sydney receives more rain per year than London

Climate Weather

Bureau of Meteorology

• http://www.bom.gov.au/

• http://www.aus-emaps.com/severe_weather.php

Atmospheric pressure

• Atmospheric pressure or barometric pressure is the pressure exerted by the weight of the air on the earth’s surface.

• Atmospheric pressure is measured in hectopascals (hPa).

• Atmospheric pressure is mapped to form isobars.• http://www.juicygeography.co.uk/animations.htm#do

wnloads/flash/highpressure.swf

Isobars

• Are lines on a synoptic chart joining places of equal atmospheric pressure.

• To estimate atmospheric pressure you need to refer to the two nearest isobars. e.g. if point “A” is situated half way between 1020 hPa and 1024 hPa, “A” would be > 1020 but < 1024 hPa.

Atmospheric Pressure readings

How do they get the land and sea readings?

What do all these dots form when they are linked?

Isobars

How do you work out which are high pressure cells and which are low pressure cells?

An isobar is a line on a map joining places of equal atmospheric pressure

Synoptic Charts• Synoptic charts or weather maps provide a snapshot of

the weather experienced at a particular place at a certain time.

• They show information relating to air pressure, air masses and fronts, cloud cover, wind speed, wind direction and rainfall.

• This information allows us to make predictions relating to temperature, humidity, ocean conditions and the likely weather for the next few days.

Synoptic ChartsSynoptic Charts

What is this feature?

What does the shading refer to?

What is the wind speed and direction?

What is the air pressure?

Pressure cells - are defined by the patterns formed by isobars. •Are these high pressure cell s or a low pressure cells?

•How can you tell?

• http://www.bom.gov.au/lam/Students_Teachers/pressure.shtml

• http://www.bom.gov.au/lam/Students_Teachers/Worksheet23.shtml

High pressure cells (anticyclones)

• occur where atmospheric pressure increases towards the centre of the system. High pressure systems are characterised by light winds, clear skies, dry weather and a high diurnal (daily) temperature range.

• A ridge is an extension of high pressure from a high pressure system.

• http://www.bom.gov.au/weather/national/charts/synoptic.shtml

High pressure cells

•Why does the air descend?

•Why does the air moves outwards?

Typical weather associated with High pressure• light winds• clear skies, dry weather • higher diurnal (daily) temperature range i.e.

hot days (sun rays maximum effect) • cool nights (because of lack of cloud cover). • Frosts are likely in winter.

Highs can bring rain from onshore warm waters

Low pressure cells (cyclones or depressions)• occur where atmospheric pressure

decreases towards the centre of the system.

• Low pressure systems are associated with stronger winds, cloudy skies, rain

• a lower diurnal temperature range. • A trough is an extension of low pressure

from a low pressure system.

Low pressure cells

Ascending air

•Why does the air rise?

•Why does the air moves inwards?

Typical weather associated with Low pressure• strong winds, cloudy skies, rain and a lower

diurnal (daily) temperature range i.e. mild temperatures (sun does not have maximum effect because of cloud cover, heat trapped in at night).

• Frosts are unlikely.

Tropical cyclones (T.C.)

• Are a very intense low pressure system. They generate very strong winds, produce rough

seas and heavy rains

• Wide spread damage occurs if they make landfall (contact with

land).

A cross section of a Tropical Cyclone

Cyclone Larry 2006

What is wind?• Wind is the movement of air masses (common bodies of

air) from high pressure areas (highs) to low pressure areas (lows). The effect of this movement of air is to rebalance

the pressure in the atmosphere.

• Note that:

• the greater the difference between the high and the low pressure, the greater the wind speed will be, and

• the closer together the isobars are on the weather map, the stronger the winds will be.

Wind speed

• is determined by the closeness of the isobars. The closer the isobars the stronger the winds.

• A steep pressure gradient exists where isobars are close together.

• If isobars are far apart a place will generally experience light winds. This is called a slight pressure gradient.

Note the closeness of the isobars

Note the spaced isobars

Reading Wind Direction on a Weather Map

Sydney

N

Close up of a map

Easterly √

(Remember that we name our wind direction on where the

wind came from)

Not where its going too

x

How to Read Wind Speed on a Weather map

Legend- Wind Speed

5 km/hr

10 km/hr

20 km/hr

To work out the wind speed of an area, all you need to do is match up the wind speed symbol found on the map with the symbol found in the key

The wind speed at point A is 5 km/hr

A

30 km/hr

Calm

Wind direction

• Wind is named according to the direction the wind is coming from, e.g. south = southerly.

• Wind direction is largely determined by the location of pressure systems. 

Wind direction

Remember we always refer to where the wind is coming from!

Where has the wind come from?

12

Wind Direction – Anticyclones (High Pressure cells)

• In the southern hemisphere winds blow outwards in an anticlockwise direction from areas of high pressure.

ANTICYCLONE = ANTICLOCKWISE WINDS.

Wind blows outwards in an anticlockwise direction in areas of high pressure.

ANTICYCLONE = ANTICLOCKWISE WINDS.

Wind Direction – Depressions (Low pressure cells)

• In the southern hemisphere winds associated with low pressure systems blow in a clockwise direction towards the centre of the system. 

LOW T. C. = CYCLONE = CLOCKWISE WINDS.

Winds blow towards the centre of a low pressure system and in a clockwise direction

LOW P. C. = CYCLONE = CLOCKWISE WINDS.

Wind indicators • Wind indicators show wind speed and direction.• The feather indicates wind speed• The shaft indicates the direction from which the wind is coming• The black dot is the place that is experiencing the windy conditions

Identifying wind direction• First - Identify the type of pressure system.• Southern Hemisphere

LOW =clockwise

HIGH = anticlockwise.• (the reverse is true in the northern hemisphere)

• Wind, generally speaking, moves across the isobars

How do you read wind direction without windsticks?

The black arrows show the wind direction. High and low pressure regions do not stay in the same place. They move over the Earth's surface.

FRONTS• A front is the leading edge of change. They are the border

zone between warm and cold air. There are two types of fronts:

• Warm fronts occur when warm air is pushed into a cold air mass. These are very rare in Australia. They result in drizzle and light rain over a few days.

• http://www.rnli.org.uk/upload/complete_eCD/fscommand/pop_up_safety.htm Go into sailing and search for weather fronts

A warm front

Cold fronts are far more common in Australia and occur when cold air is pushed into a warm air mass. This forces the warm air to rise causing a number of changes:(a) Decrease in temperature: cold air replaces warm air.(b) Change in wind direction and sometimes speed.(c) Build up of cumulonimbus or rain bearing clouds.(d) Increase in humidity: corresponding to a build up of clouds.(e) Probability of rain.

Make up an acronym to remember these changes.

A cold front

Temperature and humidity:

• are related to the wind. Winds pick up the characteristics of where they form – sea or land – these are called source regions

Remember:• Winds off the land are generally hotter and

drier.• Winds off the sea tend to be cooler and

wetter (greater moisture = greater humidity).

Humidity• Humidity is the amount of water vapour in the

atmosphere A high humidity means there is a lot of water

vapour, and a low humidity means a little. The humidity level varies with temperature. The

warmer air is, the more moisture the air can hold as vapour. The colder the air is, the less moisture the air can hold.

Humidity is measured as a percentage, relative to the saturation point where the air can hold no more water vapour (i.e. 100 percent humidity).

Types of rainfall: Convection

http://www.youtube.com/watch?v=RkgThul2El8

Types of rainfall: Orographic

http://www.youtube.com/watch?v=BVykQfRC_aIhttp://www.radioblogclub.com/open/51998/elevation_u2/U2_-_Elevation

Elevation U2.url

Orographic RainfallOrographic Rainfall

The dry air mass becomes warmer, with little chance of rain. Deserts are often found on the leeward side of large mountain ranges

Warm moist air approaches a mountain barrier

The air mass is forced to rise as it hits the mountain and condenses into clouds

Orographic rainfall occurs on the windward side of the mountains

The air mass, now drier, flows down the leeward side of the mountains

Types of rainfall: Frontal

http://www.youtube.com/watch?v=D88dYNFyBq8http://www.bbc.co.uk/schools/gcsebitesize/geography/weather/elementsofweatherrev6.shtml

Flash video on types of rainfall

Show Weather Rainfall wmv

http://blip.tv/scripts/flash/blipplayer.swf?autoStart=false&file=http://blip.tv/file/get/Gatm-Rainfall922.flv?source=3

Seasons• are determined by the location of various

pressure systems.

Remember: • Summer = Lows over Northern Australia

and Highs over Southern Australia.• Winter = Highs over Northern Australia

and Lows over Southern Australia.

Summer weather map

Where are the different cells located?

Winter weather map

Where are the different cells located?

Clear skies allow the sun’s rays to have maximum effect. Daytime temperatures

are usually high.

At night, clear skies allow heat to be lost causing temperatures to fall. In winter frosts are likely.

Why Do Climates Vary?

Factors Affecting The Climate

What makes a certain place hot, cold, wet, dry, windy…?

Your Ideas

On the A4 paper provided and working in pairs:

Quickly sketch as many ideas as you can as what might cause temperature and rainfall to be different at various places.

You have 3 minutes

World Pattern of Climate

The climate of a particular place on the earth’s surface depends on 5 main factors.

Latitude: Affects temperature

radiation from the sun is stronger and more direct at the equator. Places at the equator are therefore generally hotter than the places near the poles. Also seasonal differences are more obvious away from the equator.

Now copy fig 5.3e from p109 in your text

Latitudehttp://people.cas.sc.edu/carbone/modules/mods4car/

ccontrol/controls/latitude.html

• The sun’s rays are concentrated at the equator but spread out at the poles.

At the Poles the sun’s rays covered a larger surface area, therefore heating is

less efficient.

At the Equator, the sun’s rays covered a smaller surface area, therefore heating is

more efficient.

At the Equator the sun’s rays also have to travel through less of the Earth’s atmosphere, therefore more heat energy reaches earth.

Altitude (elevation):

• The air is generally thinner and therefore colder higher up in the mountains than it is at sea level. Also precipitation (rainfall and snowfall) is generally affected by mountain ranges as moist air will be forced to rise over the mountains (orographic rainfall). This will cause the air to cool and then condense into cloud.

• http://www.abc.net.au/science/articles/2008/08/21/2342845.htm?site=science/askanexpert&topic=latest

Everest.

The higher the relief (elevation), the lower the temperature, about

6degrees C for each 1000 metres.

Distance from the sea:

• The ocean acts as a stabilising influence on temperatures as the sea heats and cools more slowly than the land. Thus diurnal (daily) and annual (yearly) ranges of temperature are smaller near the coast and greater in inland areas. This means that inland areas generally have hotter summers and colder winters than coastal areas. Also moist air near the coast may result in more rainfall in coastal areas than places inland.

Distance from the Sea• In the summer, the sun heats the

land quickly but it takes longer to heat up the water which is large and deep.

http://people.cas.sc.edu/carbone/modules/mods4car/ccontrol/controls/landwater1.html

• However, the water stores heat for longer and so in winter, the temperature of the sea is warmer relative to the land and so keeps coastal places warmer.

Ocean Currents:

• Cold ocean currents cool the air and generally cause dry conditions along the coastline. Warm ocean currents will warm the air and cause warmer, wetter conditions.

• http://people.cas.sc.edu/carbone/modules/mods4car/ccontrol/controls/ocean.html

Also known as the North Atlantic Drift.A current of warm water

that travels from the Gulf of Mexico.

This, along with the prevailing South-

Westerly wind, enables a relatively warmer

climate compared to areas on the same

latitude.

Prevailing Winds• These are the winds that

blow most often. • Winds can affect

temperature and precipitation.

• Winds blowing over tropical oceans bring warm and wet weather.

• Winds blowing from the poles and over land bring cold and dry weather.

Length of day & Night

• Because the earth’s axis is tilted at an angle of 23.5 degrees, there are seasonal differences in the number of daylight hours. The shorter the day the less opportunity there is for the earth to absorb heat.

Sea heats up slowly and cools

slowly.

Land heats up quickly and cools

quickly.

The Seasons

• Seasons are created by the combination of the earths tilt and its orbit around the sun.

• The distance between the earth and sun is about 149 million kms. The earth rotates around the sun in an elliptical, or oval shaped path and takes about 365 days or 1 year to complete an orbit.

• The earth also rotates in an anti-clockwise direction about its north-south axis, an imaginary line that runs between the poles. It takes 24 hours for the earth to spin around once, and this rotation creates day and night. When one half of the world is in darkness, the other is in daylight.

• The earth is also tilted about 23.5 degrees on its axis. So, depending on the time of year, certain latitudes of the earth incline toward the sun more than others. Throughout the year different areas, particularly those that are far from the equator, receive more or less solar radiation. If the earth did not tilt, we would not have seasons.

• During summer in the Northern Hemisphere the longest day (the summer solstice) occurs when the sun is directly over the tropic of Cancer. As the earth continues its year long orbit the North Pole tilts away from the sun, and the South Pole tilts towards the sun.

• The equinox is when the sun is directly over the equator. The Northern Hemisphere winter solstice (the shortest day) occurs when the sun is over the Tropic of Capricorn.

World Sunlight Map

• http://www.die.net/earth/