ACTIVITY 4: Be a weather presenter

OverviewMeteorologists use weather maps, satellite images and weather radar to produce a weather forecast. They also use atmospheric pressure, temperature, moisture and wind speed data to predict weather.

Weather mapsOn a daily weather map, see below, there will be meandering patterns of relatively high and low pressure systems over Australia. It is these systems that generate variations in wind, temperature and rainfall. In particular the direction and speed of the wind is closely related to the distribution of mean sea level pressure.

In the southern hemisphere the wind flows clockwise around low pressure systems and anticlockwise around high pressure systems. The strength or speed of the wind is related to the spacing of the isobars; closer means stronger winds.

Typical weather map for Australia. Wind direction is shown with the red arrows. Pressure is shown in hectopascals (source BOM www.bom.gov.au).

The main feature of a typical weather map, such as the one shown here, are:

Regions of high and low pressure, delineated by a pattern of isobars. The isobars are generally drawn at intervals of 2 or 4 hectopascals, depending on the scale of the map.

Cold and warm fronts that delineate major boundaries between air masses. These are shown as a bold line with either triangles for cold front or semi-

circles for warm fronts along it. Troughs of low pressure, shown in dashed lines. Areas where rain has fallen in the past 12 or 24 hours, shown by hatching. Surface wind direction and speed at spot locations. The direction from which the wind is

blowing is designated by an arrow shaft and the speed by barbs along the shaft. In some cases weather maps are overlaid on satellite images whereby cloud bands

associated with fronts and low pressure systems are often readily identifiable (source BOM www.bom.gov.au).

SatellitesSatellite-based data has made an immense contribution to Australian meteorology and is essential to weather forecasting and climate research. There are two basic types of weather satellites:

i. Polar-orbiting satellites take measurements from an altitude of 850km at several wavelengths. In the visible region of the spectrum the photographs are of the earth and its clouds during daylight hours. Infra-red images measure the temperature of the surface of the earth, and clouds, night and day. Such satellite images give information on the extend of fog, flood waters, snowfields and pack ice; on sea surface temperatures and wave characteristics; on temperatures, humidity’s and pressures; and on winds, which can be derived from cloud movements.

ii. Geostationary satellites revolve around the earth at a height of 36,000km over the equator at the same speed to earth rotates. Successive images provide a moving picture of the clouds as they form, are carried by the winds, and disappear. Wind speed and direction at different levels in the atmosphere can be calculated by such sequences (Source BOM www.bom.gov.au).

Interpreting weather from satellite images

A – Monsoon cloud clusters composed of heavy thunderstorms.B – Large cloud-free area typical of summertime in the Australian dessert.C – Cold front.D – Cumulus clouds behind a cold front – a mix of showers and clear skies.E – Spiral cloud indicating a low pressure system.F – A slow moving rain depression.G – A tropical cyclone. Note the eye.H – New Zealand – under its ‘long white cloud’.I – A cut-off low pressure system bringing bad weather to Victoria.J – Warm front (rarely seen over Australia) (Source BOM www.bom.gov.au).

Weather radarMeteorologists have long valued weather radar’s ability to depict rainfall location, movement and intensity. Australian meteorologists can draw radar imagery from 43 sites. There is particularly thorough coverage on northern coastal areas subject to tropical cyclones.

Radar antennas transmit pulses of radio waves in a highly-focused beam; when these pulses strike a target, reflected energy captured on a receiver depicts the location and intensity of rain, hail, snow and drizzle. Typical displays shown on TV and the Bureau’s web site use colour coding to indicate levels of estimated rain intensity. Below is an example of a rain radar image showing the different intensities of rain (source BOM www.bom.gov.au).

AimTo understand how to read a weather map, satellite image and radar image.

Objectives To recognise patterns in weather maps To recognise patterns in satellite images To describe the key features of a high pressure and low pressure system

Tasks1. Introduction to extreme weather images

Show PowerPoint 1, 2 and 3. Initially ask students to identify the weather phenomenon in the photos. Explain the phenomenon if needed.

Show PowerPoint 2: Cyclone Yazi 3 February 2011(category 5) (source: BOM). There is an additional video of the weather map you might like to show students -www.youtube.com/watch?v=GuDyTfvjiX0

PowerPoint 3: Victorian floods 3 September 2010 (source: BOM).

2. Weather maps Show PowerPoint 4. Ask students if they have seen a weather map and if so, where. Ask students what a weather map can tell us. Then explain how to read a weather map. A weather map illustrates the meteorological conditions of an area at a specific time. A weather map not only allows us to see what the weather is currently doing, it also shows the observer what type of weather to expect during the hours and days ahead.Show PowerPoint 5. How to read a weather map. High pressure = H and low pressure = L.Isobars are lines of equal air pressure. Isobars are labelled with a number which represents the air pressure in hectopascals or millibars. The air pressure is higher near the centre of a high-pressure weather system, while lower near the centre of a low-pressure system. Isobars that are generally closely spaced mean strong winds, which generally go hand-in-hand with low pressure systems. Bars that are spaced far apart generally indicate calm, high pressure systems (blue skies).

3. Explain to students the following activity enables them to use the information on PowerPoint slide 5 to read a weather map. PowerPoint 6 provides an example.Show PowerPoint 7. Students go to www.bom.gov.au/australia/charts/ > Numerical Weather and Ocean Prediction Maps > Interactive Weather and Wave Forecast Maps.

Students work in pairs, choose a map from a particular date and save the picture.

Students then annotate and locate the following features on the weather map: High pressure system Low pressure system Air pressure Strong winds Light winds What is the weather doing at your current location?

4. Satellite images and radar images Show PowerPoint 8. Watch the video about satellite image and rain radar images. Show PowerPoint 9. Radar (radio detection and ranging) images predict when and where it will precipitate. Satellite images predict cloud cover and also show wind speed and wind direction.

5. Show PowerPoint 10. Students choose a satellite image from the BOM site and note observations. This slide provides an example.

Show PowerPoint 11. Students go to www.bom.gov.au/australia/charts/ > Weather and Warnings > Australia > Satellite Images.Students work with the same partner as before and choose a satellite image (choose the same date as before). Save the image. Read the observation made by the BOM. Note the findings about cloud cover and precipitation. What is the weather doing at your current location?

6. Show PowerPoint 12 and 13. To determine the students’ level of understanding ask them to look at the following weather map image and to identify the best day for a picnic in Melbourne. All the images were taken at 11am. A: As there is a high over Melbourne on Tuesday 15 November this will provide fine sunny weather.

7. Meteorologist presentation Show PowerPoint 14. Students watch the weather presentation by Channel 9 weather presenter Livinia Nixon. www.youtube.com/watch?v=xPVmTRJ1ggEWhat does she talk about? How does she stand? Who does she look at?

8. Make own meteorologist presentation Show PowerPoint 15. Students make their own weather presentation and present it to the class. Students use the weather forecast map data and satellite image data from before to do this. Students should print a copy of their weather map and satellite image and refer to these images throughout the presentation. Students could use iphone, flipcams or video cameras to record their presentations, which can be played to the class. One person films the first half whilst the other presents then vice versa.

9. Class presentations Students should present their videos to the class.

Duration2 hours

Materials Journal – paper and pen style or digital journal Computer, netbook or laptop with internet access White board or interactive white board for teacher presentation PowerPoint – a suggested PowerPoint has been provided to supplement the session. A

suggested order for the presentation is included iPhone, flipcam or video camera.

Resourceswww.bom.gov.au/lam/climate/levelthree/analclim/analclim.htmBOM – Climate educationPredicting the climate: Why do we need to predict the climate? Can we predict the climate? Improving prediction.

www.bom.gov.au/lam/forecast.shtmlBOM – Weather educationHow do we forecast the weather: Observations, analysing the data and preparing the forecast.

www.bom.gov.au/lam/Students_Teachers/pressure.shtmlBOM – High and low pressure systemsIn addition to information on these systems, this also provides animations that might be useful to show students.

www.metlink.org/weather-climate-resources-teachers/weather-systems-video.htmlRoyal Meteorological Society UKWeather system video series. In the series weather systems are explained, why the happen and how to understand weather systems.

Suggested post activities

Predicting the weatherStudents use the weather map image from PowerPoint 12 and 13 and predict the weather for Melbourne on the following day, Wednesday 16 November. Students need to study and compare the two weather maps and understand the weather is moving in a west to east direction. As a

result I would predict the low pressure system over Perth will slowly move its way over towards Victoria.

Animate a series of weather mapsIf students have good IT skills they will be able to collect a series of daily weather maps and animate them. They could do this by scanning, naming and sizing the images appropriately.