Photo: John Tann
The Bureau of Meteorology (BOM)’s radars have been detecting rain in NSW skies despite it being dry on the ground.
A BOM spokesperson told TDA “it is possible” its radars are confusing rain with Bogong moths migrating south.
Radars detect precipitation by sending out waves, with things like ash, birds, and insects sometimes wrongly setting off the radar.
Here’s what you need to know.
Background
Weather radars work by sending out radio waves.
If these pulses of radio waves hit water, they reflect back to the radar.
This is called an echo.
The longer the echo takes to return, the further away the water is from the radar.
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The strength of the echo can indicate if the precipitation is rain, hail or snow.
On its website, the BOM says radars are “useful” but “not perfect”, and can pick up echoes from insects, birds, aircrafts, smoke or ash.
Is it the moths?
Over the past month, Bogong moths may have been triggering the radar, particularly in eastern NSW.
Strong winds have blown large numbers of the moths off their usual migration path.
A BOM spokesperson told TDA that it is “possible that radars... are detecting Bogong moths,” rather than rain.
They said this does not mean the radars are “malfunctioning”, however.
The spokesperson explained that newer radars are able to correct instances where echoes are not caused by precipitation by sending out two sets of radio waves, giving the BOM “extra information”.
In NSW, Sydney’s Terrey Hills and Yeoval in the central west have this capability, but Wollongong and Newcastle’s radars “can’t do this filtering”.
