Like a lot of fire pushed across eastern Australia in January 2020, a deadly haze settled in Melbourne, a clear signal for residents to stay indoors. Raising their heads, however, is a less visible signal: Cellular data is flying through the air in a different pattern, one that scientists can use to better understand and predict severe smoke incidents in the future.
Cell signals high up in Melbourne are associated with an atmospheric quirk known as a temperature reversal. Typically, you will find warmer temperatures near the earth, where the sun warms the surface, and cooler temperatures higher in the atmosphere. However, true to its name, it is transferred to an opposite temperature.
If a coating on a city tire absorbs the sun’s energy, it prevents most of the radiation from heating the surface. It creates a layer of warm, dry, smoky air that sits on top of the cooler air at ground level. “You have this double process,” says Monash University atmospheric scientist Adrien Guyot, lead author of a new ROLE in the journal AGU Developments describing the research. “There’s warming on the surface, and the fact that the ground isn’t as warm as usual.”
It has done strange things with signals transmitted between cellular antennas on top of Melbourne buildings. (Guyot and his colleagues are specifically looking at antenna-to-antenna communication on the network, not how they connect to mobile phones.) Usually when these antennas are talking to each other, the signal will fly more or less directly between them. But a fluctuation in temperature creates a kind of cap on the atmosphere, causing the ground signal to bend.
These are known as “anomalous scattering conditions,” meaning that a signal will travel, well, anomaly. “It shall rise from the earth, and then ascend again, and afterward it shall rise from the earth, and ascend again. That is why it is trapped in the inversion layer, ”said Guyot. Because the signal is distorted, the travel time between the antennas is different than it would be in normal conditions, if its path is more stringent. “And because it doesn’t always come at the same time, sometimes there’s a high reception, sometimes there’s a lower reception,” Guyot added. “And the signal is very clear.”
By looking at this cellular data, then, Guyot can identify when Melbourne’s temperature change ended as Australia burned during the wildfire. In addition to trapping signals, the inversion layer is also trapped in smoke, thus creating a data record as city air quality improves. severe in the world. In the future, Guyot thinks, it may be possible to monitor cell signals for indications of where they may form and how heavy they are. That will give officers a much better idea of how fast air quality can be degrading. “If there’s a change in temperature, and if the rotation is working, you’re more likely to increase the smoke concentration as well,” Guyot said.
Consider throwing food coloring in a kiddie pool versus an Olympic pool – even if you have the same amount of dye, you’ll get much darker water in small amounts of water than large ones. The same is true for short smoke trapped in a thin layer of air close to the ground, compared to smoke that is more prevalent in an open environment. “The reversal of these changes means that smoke cannot be picked up at higher altitudes,” said Rebecca Buchholz, an atmospheric chemist at the National Center for Atmospheric Research, who did not participate in the new- ong this work. “That’s why it stays close to the ground, is very concentrated, and there’s a lot of ground pollution that affects people.”