Thursday, September 18, 2014

The iPhone 6 has a barometer!

One of my major research projects has been to explore the potential for improving weather prediction using the pressure sensors in smartphones, something I have talked about in previous blogs.

A number of Android phones has decent barometers in them, including the highly popular Samsung Galaxy series.   A Windows-based phone, the Nokia 1020, also has a pressure sensor.   Amazingly, tens of millions of phones in North America have pressure sensors!

But we now have a major new addition to the pressure-enabled smartphone stable:  the new iPhone 6.
Both iPhone 6 models have a pressure sensor

According to online reports, the iPhone6 has a Bosch BMP280 sensor (see image), with fairly good numbers:  absolute accuracy of +-1 hPa and relative accuracy for pressure changes of +-.1 hPa (normal sea level pressure is roughly 1013 hPa).   To give you a better idea of the accuracy of this barometer, the average decrease in pressure with height near sea level is 1 hPa per 8 meters (26 ft) .

Bosch Pressure Sensor

So why am I so excited by smartphone atmospheric pressure sensors?  Why do I believe they have revolutionary potential for weather prediction?

Because they offer the chance to get a extraordinary density of pressure observations, which  provides the potential to describe small scale atmospheric structures.  Structures we need to knwo about if we are to predict key weather features like strong thunderstorms.

Let me illustrate how many surface pressure observations there are.  Currently, I am getting real time feeds from two small companies, Cumulonimbus, Inc, (with the Pressurenet app) and OpenSignal (with their WeatherSignal app).   Right now, there are about 115,000 pressure observations coming in per hour from these innovative firms, (90% of them coming from the PressureNet app).  Here is the map.
Amazing coverage from DC to Boston, and around other major cities.  But there is substantial density beyond, particular east of the Mississippi and along the West Coast.

 But keep in mind that this is less than one-hundredths of the smartphones with pressure sensors.  Yes, 1/100.  In a few years there will be at least 100 millions smartphones over North America with pressure sensors. So the additional of the iPhone 6 pressure sensors will only accelerate the growth, with Cumulonimbus, Inc already working on an appropriate iPhone pressure app.

If we could collect, say pressure from 1/10 of the phones with barometers, the eastern U.S. would be virtually covered and only few uninhabited western areas would have pressure observations.

So why would these pressure sensors be a boon for weather prediction?  Because the numerical weather prediction is now going to smaller and smaller scales, and meteorologist are trying to do much better in predicting  what will happen during the next few hours (called Nowcasting).

To forecast fine-scale weather features (like thunderstorms), you need a fine-scale description of the atmosphere, and the current observational network is often insufficient.  We need millions of observations per hour over the U.S. to do the job.  Same situation in China, Europe, and the rest of the world

And pressure is the perfect surface observation:  it reflects the deep structure of the atmosphere and has less exposure problems than temperature or wind.  Pressure can be measured inside our outside a building, in your pocket or hanging on your belt.  A number of number experiments have shown that  surface pressure measurements alone can produce a very good THREE-DIMENSIONAL description of the atmosphere.  Almost sounds like magic.

I believe that dense pressure observations could radically improve weather prediction, and early numerical experiment support this claim.

But the big promise will NOT be met until we find a way to collect a higher percentage of the smartphone pressures.

Google could obviously do this.  I have approached Google about capturing pressure observations on Android phones, but Google management does not seem interested (but a number of Google engineers have been very supportive).

Another approach would be for Samsung or Apple to preinstall the code for capturing and transmitting the pressure information

Or a group with a very popular app (like the WeatherChannel or the Weatherunderground) could include the relevant code .

Anyway, it is frustrating...a huge improvement in weather prediction is possible.  Their is no major technical hurdle.  The pressure sensors are in place.  And we have not put it together.   Maybe soon....

Tuesday, September 16, 2014

Smoke Front Hits Washington State

Something happened on Monday.   Sunday was warm and clear.  The mountains appeared close and sharply defined.

Monday was just as warm, but the visibility declined greatly with Mount Rainier invisible from Seattle.  The pictures below, taken by the Puget Sound Clean Air Agency at 3 PM Sunday and 3 PM Monday, shows the degradation.

Sunday, 3PM
Monday, 3_M

The reason for this loss of visibility?  

The northward movement of smoke from large fires to the south of Washington.  The USDA Forest Service maps shows the  big fires over Oregon and California (red and blue dots are the largest fires)

A plot of the winds at Seattle Tacoma Airport with height from 10 AM Sunday (right side) to 10 AM Monday (left side) illustrates the switch of winds from offshore (southeasterly) to stronger winds from the south/southwest.  (the y axis is pressure, with 850 hPa being about 5500 ft and 700 about 10,000 ft.  The red lines are temperature)

A visible satellite image over NW Washington on Monday afternoon (from the MODIS imagery) clearly shows smoke moving northward.

Smoke can produce wonderful sunsets and those watching Monday's sunset were not disappointed.  Here are a few examples.  The first by 76johnyb and the second from Skunk Bay Weather looking north from Hansville, Kitsap Peninsula.

When the smoke reached Puget Sound, there was a clear degradation in air quality, as shown by this plot at Seattle's Beacon Hill.

Finally, maximum temperatures on Monday were roughly 15F above normal for many stations, with some locations even reaching 90F and above!

Don't believe it?  Here are the max temps around western WA.  Cooler on Tuesday....

Sunday, September 14, 2014

Huge daily temperature range hits the Northwest

Often during the late summer and early fall, a huge daily temperature range is observed at Northwest stations, particularly those away from the water.

Here is western Washington for example, stations like Olympia have risen into the 80s during day, but drop in the mid-30s at night.   Here is the proof!

And some locations in eastern Oregon have dropped below freezing!

Why have we seen such large daily temperature ranges the past few days?  Why is this season a favored one for such behavior?

Before I answer that, let me show you how cold it has gotten at night.  Here are the minimum temperatures on Saturday morning over western WA.  30s in Olympia and at inland stations around SW Washington.  Lots of 40s over land, but 50s near the water.  Some 60s southwest of the Olympics where downslope warming occurred,

Want even colder?   Here are the temps over eastern Oregon....lots of places got below freezing, particularly in low spots of the high plateau of the region.  A few locations dropped into the mid 20s.

But then the sun comes up and temperatures soared until clear skies.

Why have the minimum temps overnight got so cold?

First, the skies are clear or nearly clear.....and clear skies allow effective emission of infrared radiation to space, which produces cooling at and near the surface.

Second, nights are longer now and that allows greater opportunity for nighttime cooling.

Third, the air became much drier during recent days.   To show this, here is the plot of dew point (a good measure of water vapor) at the surface at Seattle Tacoma Airport.   A major drop from the

previous mid-fifties to the 20s and 30s.    The lower the dew point, the drier the air.    Drier air absorbs less infrared radiation leaving the surface, allow more cooling to occur.  This is because water vapor is a potent greenhouse gas, a gas that absorbs and emits actively in the infrared. Water vapor absorbs some of the infrared radiation leaving the planet and emits some of it back down to the surface.  So the drier air promotes cooling.

By the way, dry air aloft also explains why deserts often have large daily temperature ranges. And I hear that such large daily temperature swings produce excellent wine grapes....another reason why the dry areas of eastern WA give us such excellent wines.

There are some other lesser effects. For example, the ground is relatively dry and that lessens the vertical conductivity of heat from the warmer subsoils during the night.  But that is a secondary.

So enjoy the warm days, but nights cool enough for comfortable sleep.  Today and Monday will continue the nice weather.

So enjoy the cool temperatures at nigth.

Thursday, September 11, 2014

A Very Warm Autumn and Winter Ahead?

Combine the blob of warm water over the northeast Pacific and a developing El Nino and what do you get?

Potentially one of the warmest autumns  in years.

And this is exactly what the National Weather Service's long-range forecasting system is predicting.

We start with "the blob", the highly persistent area of warm water west of the Northwest coast (described in my previous blog).   The sea surface temperature anomaly (difference from normal) for the first 8 days of September are shown below.  You can see the warm water off our coast.

Since the air that reaches the Northwest comes off the Pacific,  you don't have to be a meteorologist to understand that they will tend to warm our area.  The warm blob has been very persistent and will certainly remain in place for the next month or two.

And then there is the developing El Nino (associated with warmer water in the central and eastern tropical Pacific).  Here is the latest prediction from the NOAA/NWS Climate Prediction Center.  Roughly an 65% chance of El Nino this winter.

 And what do El Ninos typical favor in the Northwest?  Warmer than normal temperatures. Here are the typical temperature anomalies (from climatology) for some previous El Ninos... the orange/red colors are above normal

So we have both the warm blob and El Nino working together for warmth.

But what does the National Weather Service's fancy Climate Forecast System (CFS) say?  A sophisticated coupled ocean/atmosphere combination that takes everything into account?  Here are the air temperature anomalies (right above the surface) for  October-November-December.   Warm.

The El Nino should rev up during the winter and here is the December, January, February prediction...much warm than normal (1-2 C, 2-4F).
I am not going to say anything about whether you should get a season pass to the lower ski areas in the Cascades.  Last time I did so I got complaints from certain people.

And what about the official Climate Prediction Center forecast for this fall? (see below).  Not surprisingly warmer than normal.

The rest of the winter looks the same.

Is a warm fall and winter guaranteed?   Of course, not.  But the meteorological dice are heavily weighted in this direction.

Particularly, when these two folks below combine forces.

Tuesday, September 9, 2014

Did "THE BLOB" cause our warm summer?

This has been an unusually warm summer here in the Pacific Northwest.  But why?

Several people have suggested the cause is a pool of unusually warm water over the northeast Pacific, one my colleague Nick Bond has amusingly  termed "the blob."   How did this blob develop and what are the implications?

As noted above, the blob is a region of unusually warm water off the Northwest coast.  Here is the difference from normal sea surface temperature (the SST anomaly) for this summer (courtesy of NOAA).  Can you see the orange area off our coast, that is the "blob".  It represents an area of water about 2-3 C warmer than normal.

The blob developed last fall and early winter, as illustrated by the sea surface temperature anomaly maps for September 26, 2013 and January 23, 2014, shown below.

But why?

The warm blob developed last winter as a result of the unusual persistence of high pressure over the eastern Pacific.  Here is difference from normal for sea level pressure for Sept to December 2013.  WOW!   A huge anomaly with the pressure over the northeast Pacific being over 6 millibars (aka hPa) above normal.  Folks, that is a big anomaly.  And it was associated with our dry fall and early winter last year.
Nick has analyzed the impacts of this high pressure area; one associated with far less storminess than normal (storms are generally associated with low pressure regions).  With less storminess, there were fewer waves and less mixing of the upper Pacific, mixing that tends to bring up colder water from beneath the surface.   Thus, the surface layer of the ocean ended up several degrees warmer than normal and this anomaly persisted into the spring and summer.

So now you know the origin of the blob: the impact of unusual fall high pressure.  But how does that warm the air over us?

During the summer, the East Pacific High builds northward in the eastern Pacific and the air that reaches us on the typical summer day comes off the Pacific.  To prove this, here is the trajectory of air ending over Seattle on August 29th.  It was over the blob a few days earlier!

The temperature of the low-level air is greatly influenced by the sea surface temperature and thus warmer water tends to cause the air reaching us to warm.    The temperature anomaly of the blog is 2-3C (roughly 4-5F) , which is quite similar to the degree of warming above normal this summer over much of the Northwest (see graphic)

A number of you have complained about the humidity being unusually high this summer.  Blame the blob.  Warmer air can acquire more water vapor than cooler air and the amount of water vapor air can hold increases VERY rapidly with temperature.

There is, of course, a lot of interest in whether the warm temperatures this summer were associated with global warming.   It does not appear so.  The warming was caused by anomalous high pressure over the eastern Pacific last fall and there is no reason to believe that has anything to do with warming the planet from the greenhouse gases mankind emits.

One final note:  the persistent warm air was a bonanza for extended range weather forecasters.   With the warm water holding in place, our long-range computer models, such as the Climate Forecast System (CFS) accurately predicted the warm summer months earlier.  Don't believe me?  Here is the proof: the June-July-August surface temperature anomaly forecast made in March!  The reds are 1-2 C warmer than normal.  Impressive skill.