Full Breakdown
Bogong Moth Swarms Trigger False Rain Echoes on Australian Weather Radar
By Drooid · · How we work
Core Event: Radar Echoes Mistaken for Rain Across Eastern New South Wales
During the past month, weather radars in south-eastern Australia have repeatedly displayed patterns that resemble light, widespread rain each night after sunset, even though ground observations show no precipitation. The anomalies are most pronounced across eastern New South Wales and have recently been detected in northern and eastern Victoria.
Background & Context: Seasonal Migration and Historical Radar Confusion
Bogong moths (Agrotis infusa) undertake a massive seasonal migration from low-land regions to the Australian Alps each summer, moving in the millions. A similar swarm attracted to stadium lights during the Sydney 2000 Olympic Games previously confused meteorologists, who initially thought rain was approaching the venue.
Data & Statistics: Scale of the Swarm and Radar Coverage
- Population movement: Millions of bogong moths are migrating southward each night.
- Radar timing: The false echoes appear consistently at the same time each evening, matching the insects’ nocturnal flight behavior.
- Geographic spread: Initially concentrated in New South Wales, the phenomenon now extends into northern and eastern Victoria.
- Visual evidence: An image captured on October 2 over central-eastern New South Wales shows a band of genuine rain alongside a separate clump of false echoes extending from northern Sydney to the Lower Hunter region.
Official Statements & Responses
- A Bureau of Meteorology (BOM) spokesperson explained that large numbers of insects can produce radar signatures that look like very light, widespread rain, especially near sunrise and sunset. The radar equipment is functioning correctly and the echoes are not caused by malfunction or extraterrestrial sources.
- Dr Kate Umbers, associate professor of zoology at Western Sydney University, described the radar data as “absolute gold” for researchers mapping bogong moth breeding sites and migration routes.
- Prof Justin Welbergen, an ecologist at Western Sydney University, noted that radar has been used to track other aerial fauna and that a prototype system, “Aerocast,” is being refined for broader ecological applications.
On-the-Ground Reports
Citizen-science platforms tracking moth sightings have reported a close correspondence between reported moth locations and the nightly radar signals. The “moth tracker” website shows a spread of observations that mirrors the radar-detected echoes, reinforcing the link between the insects and the radar clutter.
Conflicting Reports & Gaps
While the BOM and researchers attribute most of the radar clutter to bogong moths, the bureau also acknowledged that atmospheric phenomena such as temperature inversions and ducting can generate similar false echoes. The precise proportion of the signal caused by moths versus other effects remains undetermined.
Why It Matters
The misinterpretation of insect-induced radar echoes can lead weather-app algorithms, which rely on raw radar returns, to issue false precipitation alerts. Standard forecasts that incorporate modelling, ground stations, and satellite data are not affected, but the situation underscores the need for radar data quality-control when translating signals into public warnings. At the same time, the abundant radar signatures provide a valuable new data source for ecologists studying migration dynamics and for conservation planning.
What’s Next
Researchers plan to enhance radar-based monitoring tools, extending the Aerocast prototype to automatically detect and quantify moth swarms alongside other aerial animals. Ongoing citizen-science contributions are expected to continue providing real-time observations that can be cross-referenced with radar data, improving both scientific understanding and the accuracy of weather-radar interpretation.