Sunday, December 2, 2012

Can Smartphone Observations Revolutionize Weather Forecasting?

The large Galaxy S3 has a decent atmospheric pressure sensor.
It turns out that a number of new smartphones, such as the Galaxy S3, have relatively good atmospheric pressure sensors in them.  Intended to provide elevation information for a variety of apps, these pressure sensors--if collected and quality controlled--could provide thousands, if not millions, of pressure observations each day across the nation.  The implications are huge, particularly since surface pressure is a uniquely valuable meteorological observation.  As described below, a private-sector company has already created an app to collect and display these pressures, and meteorological research (including myself and others at the UW) are doing research on getting maximum benefits from these pressure observations.

First, which smartphones have pressure sensors in them?  Right now they are mainly Android 3 phones, including: the Galaxy Nexus, Galaxy S3, Galaxy Note, Galaxy Note II, Nexus 4, Nexus 10 and Xoom.  Tens of millions of these phones have been sold worldwide, so there are undoubtedly millions in the U.S. alone.  Millions of weather observatories, if only if they were collected in real time.

One company has stepped up to the plate:  a small Canadian firm called, appropriately enough, Cumulonimbus Software.  They have developed a nice app for the Android 3 phones called PressureNet2.1  that can be downloaded for free.  This app accesses your

pressure observation and your location (smartphones use GPS and/or cell phone tower triangulation) to a central database, and allows you to view the observations taken by others.  Here is a screenshot of the graphics provided by the app:

I have been talking to the developers of PressureNet2 and they said that thousands of folks signed up for their app before and during Hurricane Sandy hit the East Coast.  Here is a plot of the smartphone pressure observations for an area of New York City during landfall. can see the pressure minimum and the calibrations were really quite good.

Pressure is a uniquely valuable many ways better than temperature or wind.  Surface pressure expresses the state of the deep atmosphere, since it depends on the weight of the air above.  Pressure doesn't have the same exposure "issues" as temperature (is the thermometer in the sun?) or wind (is the anemometer behind a tree or house?).  Pressure sensor can be inside a house or outside...doesn't really matter since the pressure is essential the same.   Pressure errors are generally easy to remove (e.g., elevation differences or errors in a particular barometer).  And you can also use the  pressure change information.

Even better a number of research groups include those at the UW are studying the use of new data assimilation methods to take advantage of pressure observations. (data assimilation is the combination of models and observations to produce the best possible three dimensional descriptions of the atmosphere.  Data assimilation provides the starting point of weather forecasts done by computers).   With Professor Greg Hakim and Graduate Student Luke Madaus we are testing the use of advanced ensemble-based data assimilation using surface pressure, with sophisticated quality control of the pressure observations.  Here is an example of a Puget Sound convergence zone.  You can see the radar an area of heavy precipitation over Seattle.

These figures show the analysis of our data assimilation system with (left) and without (right) additional pressure observations.  No contest...pressure really helps.

So imagine the possibilities.

Millions of surface pressure observations across the country EVERY HOUR, allowing us to define local scale features, such as the cold pools and dry lines associated with the initiation of severe convection.    Using these observations we could radically improve our definition and description of fine-scale atmospheric features and short-term forecasts.

This could be a major advance in weather prediction technology.  And then we can use the smartphones to provide folks with highly detailed and accurate forecasts at their location.  so the benefits flow both ways.


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