July 4th Smoke, Wildfires, and the White Sky

When you looked at this morning did you notice the hazy whiteness in the sky?   July 4th fireworks are too blame.    And such fireworks have started wildfires, including a major burn near Wenatchee.

Let's start by look at the Seattle Panocam at 6:30 AM this and yesterday mornings (below).  I bet you can see the difference.  At my home, the sky looked white near the horizon.  Why white?  More later.

Today

Yesterday, July 4.

Fireworks smoke has caused significant air quality degradation over much of the region.

The western map at 830 AM (courtesy of the Puget Sound Clean Air Agency), show poor air quality (red and purple colors) over extensive areas downwind of population ceners.

And the US EPA's AirNow graphic also show poor air quality near Wenatchee (see below)

Why Wenatchee?  Because someone ignited a major grass fire west of the town with fireworks (see map below).  That individual has been arrested.

 There is another grass fire, supposedly started by powerlines, southeast of Chelan.    The visible satellite image at 6:30 AM shows the smoke from these fires, plus the Pioneer Fire up Lake Chelan.

Plots of air quality (actually small particle concentrations) at Seattle and Marysville (both shown below) illustrate the rapid increase in smoke last night.  The Marysville numbers were crazy high (about 130).

Seattle

Marysville

Finally, why do these particles turn the sky white?

It turns out this is due to something call Mie Scattering.    When light from the sun interacts with smoke particles is it scattered by the particles in many different directions (see below)

Image courtesy of Virtual Labs

Light from the sun includes all wavelengths of visible light (from red to blue/violet).   Light appears white when all wavelengths are represented and if you were above the atmosphere the sun looks pretty white.

Large smoke particles from fireworks scatter all wavelengths of visible light similarly, thus producing a white-looking sky.  This is what is meant by Mie Scattering.  In contrast, small particles in a clean atmosphere (such as the typical gases) scatter shorter wavelengths (like blue) more (called Rayleigh Scattering), which gives the sky a blue cast.    

Heavily polluted cities in China have a lot of big particles, so their skies almost always look white.  Perhaps it is ironic that our fireworks come from China.  They export their white skies to us during our day of celebration of independence.  

The Two Most Turbulent Airports in the U.S.

Many folks are flying this summer and most are not fans of in-air turbulence.

So which airports are most prone to turbulence and why?    

And if you are flying to one of these destinations, how can you minimize the risk of a bumpy flight?

All will be revealed in this blog.

Recently, the aircraft turbulence website, Turbli, published its analysis of the most turbulent airports in North America (see results below).  The top two are Portland and Denver.

I can certainly confirm the results for Denver, to which I fly all the time (the National Center of Atmospheric Research, NCAR, is in nearby Boulder).

So why are landings and take-offs so turbulent for these locations?   

It is all about geography and nearby terrain barriers.

Portland

As shown in the map below, Portland Airport (PDX) is essentially due west of the Columbia River Gorge.

During winter, cold air and high-pressure build to the east of the Cascades, while low centers approach from the west.   The result is a strong pressure difference across the Cascades that produces strong low-level easterly winds in the Gorge that reach the airport (see model simulation below).

While the winds are strong and from the east at low levels, the winds above are generally westerly (from the west).  This produces a strong vertical wind shear (winds changing rapidly with height.

Strong wind shear is a principal driver of turbulent motions.  Summer conditions are less conducive to Portland airport turbulence.

Denver

Denver Airport (KDEN) is northwest of the city and just east of the Front Range of the Rockies (see map).

The Rockies are turbulence generators throughout the year.

During summer, and particularly from June through early September, thunderstorms develop over the Rockies during the late morning and early afternoon and then drift towards the airport.   Thunderstorms produce lots of turbulence.  

Check out his satellite picture for midday on June 23rd...you can see the cumulus clouds bubbling up on the Front Range.   Fly in from Seattle and you will fly through these clouds and will bump around considerably.

If you want to avoid summer turbulence at Denver, FLY IN or OUT EARLY before the thunderstorms rev up.  My rule of thumb:  don't fly in or out of the DIA after 11 AM during the summer.

There are few such thunderstorms during the winter, but there still is plenty of turbulence, this time from strong mountain waves downstream (east) of the Rockies (see schematic below).   Such mountain wave turbulence is encouraged by strong westerly winds approaching the crest of the Rockies for the west, a very frequent situation during the winter!

Such mountain wave turbulence can be extreme.

Happy flying!