1.
Monitoring the Climate
Climatologists identify patterns and relationships in meteorological
observations and records. Our understanding of climate variability has
advanced considerably as observation networks and technology have developed,
particularly since the introduction of satellites and powerful computers.
Australia's
first weather men
Large-scale
atmospheric circulations affecting our climate
Climate
Variability and El Niño
El Niño is one of the major climate influences in the world
and the most important one in Australia. Its impacts include decreased
probability of rainfall and it is often associated with widespread drought.
Sea-Surface
Temperatures
During El Niño events warmer than normal water spreads along
the equator into the central Pacific. The measurement of Sea-Surface
Temperature anomalies helps to determine whether climate patterns like
El Niño are developing.
Map Information
SOI
or the Southern Oscillation Index
The Southern Oscillation Index is based on the difference in
air pressure across the Pacific Ocean between Darwin and Tahiti. Strong
negative values are generally associated with El Niño, and positive
values with La Niña. SOI definition.
Drought Statement
A routine report identifying areas with long-term Australian rainfall
deficiencies. (Note that this report is issued monthly, and is based
on rainfall received up to the end of the previous month. While it is
issued monthly when required, there will be periods when no issue is
required.)
Recent
Australian temperature and rainfall analyses
2.
Predicting the Climate
Why
we need to predict the climate?
While
most of us feel the effects of climate variation, many businesses, services
and activities depend on climate forecasting to prepare adequately,
to manage risk, protect the environment, and to save lives. Climate
extremes like flood, fire, cyclones and drought cause major impacts
that can be minimised more effectively with climate forecasting.
Can
we predict the climate?
At present, we're
able to forecast out to 7 days ahead using computer weather models.
Prediction of the day to day weather in the mid-Iatitudes does not in
general appear to be possible beyond about 7 to 10 days. This is in
part due to the current limitations of the global computer weather models,
but more importantly because of the chaotic nature of the weather patterns
in the atmosphere.
In the longer term of about three to six months, some predictability
does arise for 3 monthly averages (temperature) or 3 monthly totals
(rainfall). This predictability comes from slow-moving fluctuations
in the broader climate patterns of the Pacific and Indian Ocean basins.
Even so, the Bureau of Meteorology does not attempt to make categorical
forecasts (e.g. this winter's rainfall will be 220 mm), but rather gives
estimates of probabilities that seasonal averages or totals will be
below average (in the bottom half of historical totals) or above average
(in the top half of historical totals). The weather forecasts are less
definitive, the further ahead we look.
Patterns
of climate variation
Assessment of predictability
of the climate starts by looking for patterns in the historical record
between seasonal rainfall or temperature and indices of the larger climate.
These patterns include tendencies towards wetter conditions in eastern
Australia during La Niña events and drier conditions there during
El Niño events. Other patterns such as sea temperatures are also
known to affect winter rainfall, particularly in central Australia.
Improving
prediction
Improvements in
seasonal prediction could come from the discovery of as yet unnoticed
important patterns in the historical data. It is more likely however
that improvements will come from changes in the way seasonal forecasts
are prepared. At the moment, the seasonal forecasts are prepared by
looking at the statistical relationships in the historical data between
seasonal rainfall/temperature and the ocean patterns in the Pacific
and Indian Oceans. For this sort of scheme to be successful, it has
to be assumed that the future is going to be much like the recent past
(i.e. the last 50 to 100 years).
In contrast, today's weather forecasts are prepared by looking at conditions
as they are at the moment, and projecting those conditions forward by
the use of large complicated computer models, which describe a range
of physical processes. It is thought that in the next ten to twenty
years, seasonal forecasts for Australia will be prepared in the same
way. This would allow the impact of any recent climate change to be
taken into account when preparing the forecast.
Using
the Bureau's climate information - Where to start
The Bureau's climate
prediction reports use specific terms you will need to know first.
Climate
Outlooks - Frequently Asked Questions
Seasonal
rainfall Outlook
This is a written and mapped summary of rainfall probability across
Australia over the next 3 months.
Seasonal
temperature Outlook
Rainfall
Variability and Probabilities
Includes an interactive animation along with teacher's lesson plan and
student's worksheet.
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