Weather Week 6,

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WeatherWeek 6,

• Need to understand
• Local influences on weather
• Tasmanias weather!!

This is the small-file version of my
PowerPointpresentation. Please e-mail me if you
want thelarger file with all photos. John Todd
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We have talked about broad scale climate patterns
and introduced some of the factors driving them,
now we move to localised weather patterns where
broad scale synoptic systems are influenced by
local topographic features and human
developments. We are also interested in day to
day variation as well as longer term averages.
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Factors influencing weather

• Variation due to synoptic patterns
• High/low pressure, wind direction
• Variation due to cold or warm fronts.
• Variation due to land/water influences
• Variation due to topographic features
• Human influence heat islands

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Tasmania points of interest

• Rainfall normal and extremes
• Temperature
• Wind - extremes
• Sunshine
• Frost
• Thunder storms

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Remember global average Rainfall is about 1000mm
Bureau of Meteorology An excellent web
site www.bom.gov.au
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Rainfall
Why high in West, low in East?
This air picks up moisture as it passes over the
ocean
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This illustrates one important local influence on
rainfall orographic lifting, with a rain shadow
on the down-wind side of the mountains
See picture on lecture handout or on page 207 of
Christopherson This is an important feature of
air movements that you should understand.
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Highest ever 40.8oC Bushy Park 1945 Hobart 1976
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Lowest ever -13.0oC Central Plateau 1983
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Summer
TEMPERATURE
Highlands cooler than lower areassummer and
winter as expectedbecause air temp. decreases
with altitude
The summer maximum and winter minimum
temperature patterns showsome important
differences. Why?
Winter
Strong coastal influence on winterminimums
(water cools slower thanthe land)
Latitude and warming effect as dryer airdescends
over mountains
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Tasmanias Temperature Illustrates

• Obvious seasonal effects
• Influence of wind direction (warm off Australian
  mainland, cool off Southern Ocean) (large
  influence on day-to-day temp.)
• Altitude
• Moderating effect of coast
• Influence of rising (cooling) or falling
  (warming) air
• Latitude (off-set by Bass Strait - Why?)

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Wind

• Storm damage
• Wind resourcewind farms, King Is, far
  north-west

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Halls Creek very different pattern. Why?
Note that in summer months, not much difference,
but inwinter a big difference.
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Frost

• Above 300m elevation, frosts can occur throughout
  the year in Tasmania
• Below 300m it is rare to have frosts in summer
• Why do frosts occur?

Photo Burroughs et al. 1997
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Frost Formation

• Frost, clear, cold night No frost, under
  tree or when cloudy

Heat radiating out into space
Layer of very cold airclose to the ground
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World-wide 8 million lightning flashes per day
(100 every second)Earths electric
field of 100 volts per metre
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Cold Fronts
Look at the diagram on the lecture handout oron
page 209 of Christopherson
Christopherson p 209
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Moving, on average,500km per day towardsthe east
Visible light image, 8 April 2002, Bureau of
Meteorology
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Summary

• We have applied some of the basic principles of
  atmospheric air movements to gain an
  understanding of Tasmanias weather
• Temperature
• Rain
• Wind
• Frost/thunder storms

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Next Week

• Last of the climate/weather lectures
• Climate change
• Human influence on global climate
• Information
• Australian Greenhouse Officeweb site
  www.greenhouse.gov.au
• Bureau of Meteorologyweb site
  www.bom.gov.au/climate/