Download Year 9 Geography

Year 9 Geography
Understanding Climate and Weather
Climate affects every part of our lives - from when and where we go on holiday to
how our food is produced and what it costs. Knowing about the climate can help
us in many ways, such as helping us plant crops at the right time, designing
comfortable houses to live in or planning for possible climate change.
Climate & Weather: what's the difference?
There is a variety of ways to explain the difference. Here are a few that the Bureau
of Meteorology have come up with that may shed some light:
Climate is what you expect; Weather is what you get.
Climate is about long-term records, trends and averages;
Weather
is the day to day experience.
Climate is the sum or synthesis of all the weather recorded over a
long period of time. It tells us the average or most common
conditions, or extremes, or counts of events, or frequencies. Weather
is a description of conditions over a short period of time - a "snap
shot" of the atmosphere at a particular time.
If weather is the
watch then climate is the calendar.
What is weather?
The weather map is possibly the best known map of all—there’s a weather
map on almost every television news bulletin. Everyone has an opinion about
weather and everyone knows something about weather maps! The weather
map is also called a synoptic map or synoptic chart. It shows us a synopsis—
which means a summary—of the weather conditions at a particular time.
The main features shown on weather maps are:
• isobars
• high-pressure and low-pressure cells
• cold and warm fronts
• winds
• areas with rain in the previous 24 hours.
The most obvious feature on weather maps are lines called isobars. Isobars
are lines that join places of equal air pressure, measured in hectopascals (hPa)
by sensitive instruments called barometers. Isobars show us the differences in
air pressure across Australia. The average air pressure around the world is
1013 hectopascals. Isobars surround cells of higher and lower air pressure,
labeled High (or H) and Low (or L). The closer the isobar lines are together,
the stronger the wind is likely to be. When lines are far apart, one can expect
calm conditions with light winds.
QuickTime™ and a
decompressor
are needed to see this picture.
Questions
1.
2.
3.
4.
5.
6.
What is an Isobar?
Draw the symbol for a low pressure trough
What is the symbol for a low pressure cell?
What is the symbol for a high pressure cell?
Draw the symbol for a cold front?
Refer to the map above. Which states have received rainfall in the previous 24
hours.
7. In which season was the above Synoptic Chart taken?
When air is cooled, it becomes heavier than the surrounding air, and falls. This
increases its weight on the Earth’s surface, causing high-pressure cells of air to
develop. When air is warmed, it becomes lighter than the surrounding air and tends
to rise, reducing its weight on the Earth’s surface, resulting in the formation of lowpressure cells of air.
Differences in air pressure cause air to move. Falling air in a high-pressure cell causes
air to flow outwards from the centre towards surrounding areas of lower pressure.
Here it replaces the rising air in the centre of the low-pressure cell.
When the isobars on a weather map are close together, the difference in air pressure
is greater, winds are faster and stronger, and changes in our weather can be sudden
and dramatic. When the isobars are widely spaced, the difference in air pressure is
small, winds are light and changes in our weather are usually more gradual.
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
Under low air pressure systems, air rises. This process drags in air from surrounding
areas as shown in the diagram above. This is how wind is created. The more rapidly
the air rises, the stronger the wind becomes that is being dragged in to replace the
rising air.
Questions
1. What two things happen in a low air pressure system?
2. What causes wind?
Cold and Warm Fronts
Cold air and warm air do not mix easily. When cold winds come up from
Antarctica, they push into warmer air over southern Australia. The air
temperature drops, winds change direction and pick up, and rain is often
associated with this type of change. This is shown on a Synoptic Chart by a line
with triangles on it. Conversely, sometimes warm winds push south from the
desert and warms up southern regions of Australia. This is shown on a Synoptic
Chart by a line with semi-circles on it.
Questions
1. Describe the characteristics of a Cold Front.
2. Refer to the Synoptic Chart on the previous page. Use a highlighter to identify
the location of the Cold Fronts on this map.
3. Which Australian cities will be affected by a cold front in the next 24 hours
according to the weather chart on the previous page.
4. Place a letter X on the synoptic chart in the location where air pressure is
highest. In which direction is the air moving to the east of this location?
5. What was the air pressure over Merimbula at the time this Synoptic Chart was
constructed?
Tracking Weather and the Forecast
Based on surface weather reports, reports from weather balloons and aircraft,
and satellite information, computers develop forecast models that predict
possible sea-level air pressure, rainfall, temperature, humidity and wind
conditions for five to seven days in advance. These models are checked and
changed—in many cases, every 12 hours—to reflect the latest weather
information.
The weather report—on television, radio or the Internet, or in the daily
newspaper—is based on forecast information supplied by the Bureau of
Meteorology (BOM) and other agencies such as the US National Oceanic and
Atmospheric Administration (NOAA). Meteorologists use this information to
prepare weather reports that include weather maps (synoptic charts that
show the state of the atmosphere at the time the report is prepared), forecast
weather maps for up to five days ahead and forecast temperatures and
rainfall.
Pick the forecast
Questions
1. According to the 4 day forecast on the Synoptic Charts from the previous,
on which days is Merimbula expecting rain in the forecast period?
2. Name an Australian city likely to receive the light winds on Friday.
3. Which Australian state is likely to receive the highest winds over the
forecast period?
4. Describe the weather conditions for Darwin during the forecast period.
5. What will the air pressure be on Friday in Sydney according to the Synoptic
Chart?
6. Describe the forecast for Melbourne on Saturday.
7. In which direction is the wind forecast to blow on Friday evening in Perth?