Lecture 1 Part 4

Climate Indices and Fire Season Planning

The sudden oscillation index, along with other indicators, is frequently used to inform decisions related to climate and weather patterns. These indices play a crucial role in planning for events like the upcoming fire season.

El Nino, La Nina, and Their Effects in Queensland

In Queensland, the El Nino Southern Oscillation Index, encompassing both El Nino and La Nina, significantly influences climatic conditions. This influence is observed through:

Mean Sea Level Pressure: Red indicates above-normal pressure, while blue indicates below-normal pressure.
Precipitation: La Nina brings wetter conditions, while El Nino results in drier conditions.
Outward Going Long Wave Radiation (OLR):
- Shortwave radiation from the sun penetrates the Earth's surface.
- Thermal radiation, or longwave radiation, is then emitted back into outer space.
- The warmer the object, the greater the amount of emitted radiation and the shorter the wavelength.
- Thermal radiation ranges from approximately 3 to 100 micrometers in wavelength.
- During El Nino, increased longwave radiation escapes to the north due to drier conditions, resulting in hotter surface temperatures and less cloud cover.
- Conversely, La Nina conditions lead to more cloud cover and reduced longwave radiation escaping into space.

Z 500: Height of the 500 Hectopascal Geopotential Surface

Z 500 represents the height of the 500-hectopascal geopotential surface in the atmosphere.

Atmospheric structure is often analyzed using pressure levels (e.g., 750 hPa, 600 hPa, 500 hPa) rather than specific heights.
These pressure levels vary depending on the temperature of the underlying air.
- Warmer air causes these levels to be higher due to expansion.
- Colder air results in lower levels due to contraction.
During La Nina, the air is warmer, and the 500 hPa surface is approximately 50 meters higher. In contrast, during El Nino, the air is cooler, and the surface is about 50 meters lower.

Impacts of La Nina and El Nino

La Nina:

Above-average rainfall.
Increased occurrence of tropical cyclones.
Reduced bushfire risk.

El Nino:

Below-average rainfall.
Fewer tropical cyclones.
Increased bushfire risk.
Lower minimum temperatures due to less cloud cover, allowing more longwave radiation to escape.
Increased range of temperatures, leading to a higher frost risk and increased heatwave conditions.

Tropical Cyclone Naming

Tropical cyclones are named using people's names, following an alphabetical order. This practice originated in Australia with a New Zealander heading the Bureau of Meteorology, initially naming cyclones after politicians.

Atmospheric Moisture and Rainfall

Warmer atmospheric conditions allow for a higher water vapor content. Theoretically, for every degree of temperature increase, the atmosphere can hold approximately 7% more rainfall. In practice, this can be around 10% to 13%, particularly over topographic features.

Seasonal Forecasts

Seasonal forecasts, based on climate conditions, such as La Nina, are used in agricultural decision-making. Current forecasts indicate a high chance (over 60%) of above-average temperatures across Australia.

Indian Ocean Dipole (IOD)

The Indian Ocean Dipole (IOD) is similar to El Nino but occurs in the Indian Ocean. It is quantified by measuring water temperatures off the coast of Africa and to the northwest of Australia. In 2018-2019, a positive IOD phase, combined with an El Nino event, led to severe drought conditions.

Positive IOD

Unusually warm water off the coast of Tanzania and north of Madagascar.
Cooler waters near Indonesia.
Reduced rainfall in parts of Australia.

Negative IOD

Unusually warm water to the north of Australia.
Cooler waters in the western Indian Ocean.
Increased rainfall in southeastern Australia, facilitated by northwest cloud bands.

Climate Model Forecasts and Ensemble Mean

Climate model forecasts are generated using multiple models with varying physics routines and sea surface temperature models. The divergence among these models is visualized, and the ensemble mean, representing the average of all models, is used for forecasting due to its higher confidence level.

Northwest Cloud Bands

Northwest cloud bands transport water vapor from warm ocean regions, leading to precipitation mainly in southeastern Australia.

Practical Considerations for Field Work

For field work, it's important to bring:

A drink bottle
A sun hat
Enclosed footwear
Sunscreen

Course Assessment

The formal assessment items include:

An Essay (25% of the course mark)
A Field Report or Literature Review (25% of the course mark)
An Exam (50% of the course mark)
Practicals (Pass/Fail)