Weather

Weather is the state of the atmosphere in a certain place at a certain time. Weather always changes and is different all around the world. It depends on many elements. It may be warm and sunny in one place but cold, windy and rainy somewhere else.

Climate refers to the weather conditions in a certain area over a longer period of time.

Weather is important to everyone. It affects our daily lives in many ways. What we wear depends on the weather. Weather affects the way plants and crops grow.Extreme weather may lead to dangerous situations. Hurricanes and storms may even kill people and destroy houses and roads.

Our weather is made in the troposphere—the lower layer of the atmosphere. Our atmosphere consists of 78% nitrogen and about 21 % oxygen. Water vapour in the atmosphere produces clouds, rain, snow and fog.

Elements of the weather

Temperature

Temperature is one of the most important elements in our weather. How warm or cold it is depends on many factors.

The temperature of the air is higher when sun rays hit the earth. Temperatures also vary from season to season. During the summer the earth’s axis is tilted towards the sun, so the rays of the sun hit us more directly. The days are longer and we get more sunlight.

Temperatures also depend on altitude. It gets colder when you are higher up in the mountains and it’s warmer near sea level. The temperature decreases about 0.7°C per 100 metres.

Places near the sea usually have more moderate climates than areas far away from the coast. There the summers are very hot and winters very cold.

The average global temperature 

Air pressure

Air pressure is the weight of the air. Cold air is heavier and sinks to the ground while warm air rises. When air moves it produces wind. Air moves from high pressure areas to places where the air is not so dense.

Humidity

Humidity is the amount of moisture that is in the air. Warm air expands and can hold more moisture than cold air.

When the air can hold no more moisture it forms small droplets called clouds.

Meteorologists often measure the relative humidity in the air. That is the amount of water in the air compared to how much water the air at that temperature can really hold. Relative humidity can reach nearly 100%. The air is completely saturated with water.

Precipitation

Precipitation is what comes down to earth from the clouds in the atmosphere. The most common forms are rain and snow. Other forms include hail, sleet, drizzle.

The amount of precipitation that a place gets is different and depends on many factors. Areas near the coast get more rain than places in inner regions. Sometimes high mountains stop wet air from getting to other places.

Heavy rainfall

Wind systems

Because the earth rotates around its axis air does not move directly from high to low pressure areas. The Coriolis effect makes windsshift . There are three big global wind systems:

• Trade winds blow near the equator between 30° north and 30° south latitude. The trade winds north of the equator blow from the northeast, those south of the equator from the southeast.When they meet at the equator they rise. Rising air leads to the formation of clouds and therefore it starts to rain. A system of clouds and rainy weather is always around the equator but it moves its position depending on the position of the sun.

• Westerlies blow in the middle latitudes between 30° and 60 ° north and south of the equator. These winds are especially strong in higher regions. This area of western winds is also called the jet stream. Airplanes travelling from west to east benefit from strongtailwinds. They need much less fuel and can travel faster.

• Polar winds are easterly winds that blow in the Arctic and Antarctic region. Fronts develop where polar winds and westerlies meet. Storms and cyclones arise around this area where warm and cold air meets.

Air Masses

Air can be cold or warm, wet or dry. When different kinds of air masses meet a front forms. When a warm front approaches , air starts to rise and forms clouds . Light rain usually comes with a warm front.

About a day later a cold front follows. Cold fronts move faster than warm fronts and often catch up with them. The cold air moves under the warm front and pushes the warm air up. Clouds and rainfall are the result. Sometimes such a front can even cause short showers andthunderstorms.

Trade winds blow from the northeast and southeast towards the equator

Weather Forecasting

Scientists who study what goes on in our atmosphere are called meteorologists. They can tell us what the weather will be like in the next few days. They gatherinformation from all sorts of instruments.

Today, weather satellites collect data from around the world. This data is entered into computers which produce weather patterns for the future.

Ten thousand weather stations on all continents observe the weather worldwide. They use many kinds of instruments to measure the condition of the atmosphere. The thermometer, for example, measures the air temperature, a barometer measures the weight of the air and a hygrometer shows how much moisture is in the atmosphere.

Weather stations use weather radar to monitor areas of rain or snow, track storms or follow the paths of hurricanes.

Weather balloons are sent into higher regions of the atmosphere and measure changes in temperature, winds and other elements A radiotransmits data back to earth.

Weather forecasts are not always accurate, partly because humans make mistakes when they enter data, partly because thecondition of the atmosphere always changes and is unpredictable.

Meteorologists can therefore predict weather over a short period of time fairly well, however long term weather predictions are veryinaccurate.

Extreme Weather

Although weather experts rely on average temperatures over a longer period of time to predict the weather, there are often extremeweather conditions.

The lowest temperature ever recorded on earth was at Vostok, a station in Antarctica. –89° C was measured in 1983 . The highest temperature was recorded in the Libyan desert in 1922 (57°C). The highest annual rainfall was measured in Cherrapunji, India , at thefoot of the Himalaya mountain range. 26 metres of rain fell over a one year period.

Heat waves and droughts in western Australia

Words

• accurate = exact , correct

• affect = to have an effect on, influence, change

• air mass = large amount of air

• air pressure = the weight of the air

• altitude = the height of a place above the sea

• amount = how much

• annual = yearly

• approach = to come nearer

• axis = the line around which an object turns

• benefit = it helps you, it gives you an advantage

• catch up with = to come from behind and reach someone or something in front of you by moving faster

• cause = lead to

• certain = special

• common = well known

• condition = state, situation

• consist of = to be made up of

• crop = a plant such as wheat or rice that farmers grow and sell as food

• cyclone = tropical storm

• data = information

• decrease = to go down

• dense = thick, heavy

• depend on = it is affected by other elements

• destroy = completely damage

• develop = build up

• drizzle = weather that is a combination of light rain and fog

• droplet = small drop

• especially = above all

• expand = to get bigger

• extreme = great, very unusual, not normal

• fairly = quite, rather

• fog = clouds that are near the ground; they are difficult to see through

• foot = bottom

• forecast = to tell what a situation will be like in the future

• fuel = substance or material like coal or oil used to make energy

• gather = collect

• global = worldwide

• hail = frozen raindrops that fall down as hard balls of ice

• hailstone = a small ball of frozen rain

• however = but

• in a row = happening many time, one after the other

• inaccurate = not exact, not correct

• latitude = distance north and south of the equator measured in degrees

• layer = part, section

• long term = for a longer period of time

• measure = to find out the amount or size of something

• meteorologist = a person who studies weather conditions and the climate

• moderate not too hot and not too cold

• moisture = small droplets of water on the air

• monitor = watch, observe

• mountain range = group of mountains usually in a line

• nitrogen = a gas that has no colour and no smell; it forms most of the earth’s atmosphere

• oxygen = a gas that is in the air and that we need to breathe

• partly = in part, somewhat

• path = route

• pattern = the regular war in which something happens

• predict = foretell

• pressure = force, weight

• radar = machine that uses radio waves to find out where an object is

• ray = line of light from the sun

• record = write down information and save it

• refer = is about

• rely = depend on

• rise = go up

• rotate = to go around an object

• satellite = a machine that is sent to space and flies around the earth at a great height

• saturate = full of

• sea level = the average height of the sea, used to measure mountains and other places

• shift = change direction

• sleet = half-frozen rain that falls when it is very cold

• state = condition

• surface = ground

• tailwind = wind that is blowing in the same direction in which you are travelling

• therefore = that is why

• thunderstorm = storm with thunder and lightning

• tilt = to move towards

• track = follow

• transmit = send back

• unpredictable = changing a lot so that you never know what will happen

• vapour = very small drops

• vary = are different

• weight = how heavy something is