Grounding the world鈥檚 commercial airliners in an attempt to stop the coronavirus crossing international borders could have an unexpected effect: weather forecasts may get less accurate.
That is because commercial planes often carry meteorological instruments, and the readings they gather feed into weather-forecasting models. With , this valuable data set has been temporarily lost.
Stan Benjamin at the US National Oceanic and Atmospheric Administration says a similar situation occurred in 2010. That spring, the ash-laden eruption of Iceland鈥檚 Eyjafjallaj枚kull volcano triggered Europe鈥檚 since the second world war, giving European weather forecasters a brief headache.
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But the coronavirus pandemic is unprecedented, says Daniel Swain at the University of California, Los Angeles. 鈥淩ight now, we鈥檙e talking about an 80 or 90 percent global reduction in traffic, potentially for months,鈥� he says.
Modern weather-prediction models largely rely on three sources: , remote-sensing satellites and planes. In 1979, several airlines, companies and national weather services to attach meteorological equipment to commercial jets and have them automatically report the weather.
Today, these planes can record the temperature, humidity, air pressure, wind speed and wind direction of a large swathe of Earth鈥檚 atmosphere. These measurements have much better spatial resolution and accuracy than satellites, providing information on conditions near-ground during take-off and landing as well as those in the jet streams, the high-altitude rivers of air that influence the weather on the ground.
This stream of high-resolution data lets us fine-tune forecast models, says Jim McQuaid at the University of Leeds. Both private weather-forecasting companies and state-run meteorological agencies use these readings and support the notion that aircraft observations assist forecasts on a range of timescales.
From March 3rd to March 23rd, the European Centre for Medium-Range Weather Forecasts (ECMWF) recorded a in European aircraft reports. Globally, there was a 42 percent reduction. The ECMWF estimates that if all aircraft readings are removed, the quality of near-future wind and temperature forecasts around typical aircraft cruising altitudes of 10 to 12 kilometres will drop by up to 15 percent.
If this is sustained, it will also have an effect on the ordinary forecasts we all rely on, says Swain. The behaviour of the polar jet stream at cruising altitudes defines the path, strength and position of many storms in the northern hemisphere. Knowing what it is doing with less certainty could make weekly weather forecasts less reliable.
Complicating things further, says Swain, is the transition from winter into spring in the northern hemisphere, a time of greater forecast uncertainty.
If flights are grounded for many months, the consequences could be significant. If so, Swain says scientists could reinforce regional forecasts by unleashing more balloons in flight-deprived locations.
Thankfully, climate forecasts shouldn鈥檛 be affected. 鈥淟ong-term climate projections simply don鈥檛 depend on knowing the exact state of the atmosphere right now, whereas weather forecasts absolutely do,鈥� says Swain. 鈥淔rom a climate-modelling perspective, this doesn鈥檛 really present any issues.鈥�
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