| 26 August 2020
The Pacific Ocean sometimes catches a fever in its Eastern tropical part (off the coasts between Central America and Peru): for extended periods of time, its surface waters are abnormally warm. These are known as El Niño episodes. Sometimes the opposite phenomenon occurs, with extended periods of colder-than-usual temperatures, known as La Niña episodes. This oscillation between cold and warm episodes has wide-ranging effects on the climate of the Earth.
El Niño and La Niña in Australia
In Australia, La Niña episodes are typically associated with large rainfall on the Eastern part of the country, as described in more details by the Bureau of Meteorology. What does this association look like exactly? and what does it sound like?
This can be explored using two datasets:
- Monthly rainfall data in Eastern Australia.
- Monthly values from the Southern Oscillation Index (SOI) with high values denoting La Niña episodes, and low values El Niño episodes.
- Opposite SOI values (-1*SOI) control the pitch and volume of a piano. El Niño episodes can therefore clearly be identified as parts with high-pitched piano notes.
- The same -1*SOI values are averaged at the seasonal scale (leading to 4 values per year, instead of 12). This seasonal series is used to control a bass, drums and cymbals, so that La Niña episodes will be low and loud!
- Rainfall values control the volume and pitch of an organ and a guitar, so only very wet months will be clearly heard.
A few other elements (a drum pattern, saturation and reverberation) are added to improve the way the result sounds, but they are not data-driven.
A few thoughts
Overall, the association between La Niña episodes and high rainfall can be seen and heard quite clearly. However the video also reveals that this association is not systematic: for instance, the La Niña of 1988-1989 did not resulted in particularly high rainfall. Conversely, rainfall was pretty high during the El Niño of 1940-1941. So while the El Niño / La Niña oscillation does influence the probability of seeing low/high rainfall, there remains some degree on randomness in this association. In addition, this oscillation is only one of several mechanisms influencing the climate of Australia. So maybe these other climate sheepdogs played a role as well?
Codes and data: browse on GitHub