A Network Of Smartphones Can Improve Short-Term Weather Forecasts

Now your phone can help predict the weather. Soon weather station might be added to the many functions of your phone. Researchers have shown that air pressure data from thousands of smartphones can improve predictions of a storm's strength, and where and when it will strike. Such a smartphone network would augment the existing system of ground-based weather stations, which, while more accurate and powerful, are expensive to expand.

That mobile observation system is based on the air-pressure sensors built into most new and high-end smartphones to help determine elevation. In a recent study published in the journal Weather and Forecasting, Mass and Conor McNicholas, a graduate student at the University of Washington, show that these sensors can also fill in the gaps of an existing weather station network and improve forecasts.

To make forecasts, meteorologists feed weather data into a computer model, which calculates a prediction of future weather. As the models have improved, they've begun to outpace the data available to them, explained Luke Madaus, a meteorologist at Jupiter Intelligence, a company that determines risks from climate change.

Current weather station networks were designed for an era when models could only simulate storms and other weather phenomena that spanned 100 kilometres, said Madaus, who started the smartphone project while a graduate student at the University of Washington. But models can now simulate weather in much greater detail, resolving phenomena down to several kilometres or hundreds of meters. So to get the most out of models, meteorologists need a denser network of sensors.

The need for better forecasts and more sensors is especially true in regions where weather stations are sparser, such as in the developing world, Mass said. While stations are lacking in some of these areas, smartphones are becoming increasingly abundant.

To see how much smartphones could help, McNicholas wrote an app called uWx that collects air-pressure data from users' phones. Pressure is a fundamental measurement because it tells you what's happening through the atmosphere above, said Josh Hacker, an atmospheric scientist at Jupiter Intelligence, who wasn't involved in the research. Measurements of pressure from a smartphone can be more reliable than, say, temperature or humidity, since pressure doesn't change if the phone is indoors, or in a pocket or purse.

Still, smartphone data can be messy. Individual sensors may not all perform in the same way. The data may not be reliable, for example, if the phone is in a car driving up and down a hill, or if it's on an elevator. The pressure change in a tall building can be as large as a change in a weather system.

To address these issues, the researchers combined information about a phone's environment such as its precise location based on GPS data and machine-learning algorithms to gauge and correct errors in the data in real-time. The correction methods also used information from nearby weather stations to smooth out random fluctuations in the smartphone data.

The improvement was modest, though, and not better than a few percent increase in accuracy. But even a small improvement could make a big difference, a slight shift in a storm's path, taking it over different geography, can mean the difference between a calm evening and downed power lines and tree branches. Those modest changes can send you across thresholds in terms of impact on society.

But as the phones make smaller-scale measurements, the data probably won't be useful for forecasting larger-scale, longer-term weather days ahead of time. Nor would this approach be useful in rural areas where smartphones are scarce.  The researchers will need to do more systematic analyses to show that smartphones are helpful through different seasons and geography, and able to forecast a variety of weather systems. There's more work to be done before it can prove to be generally useful.

The study used only about 0.1 percent of all the potential smartphone measurements in the Pacific Northwest. Getting more data could lead to even better improvements. The researchers have been working with IBM's The Weather Company, using data collected through the company's weather app. To gather more data the researchers might partner up with companies with greater access to phones. More data would help produce a more detailed and probabilistic view of how storms evolve.

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