Contrail Fest over Eastern Washington

The satellite imagery over eastern Washington this morning looked like someone had gone crazy with a white crayon,  drawing many white lines, most extending roughly east-west.

Here is a closer view.   The white lines are contrails created by aircraft.

Look very closely, and you will see some black lines as well:  the shadows are produced by the contrails stopping the sun's light from reaching the surface.

Contrails are formed by the combustion of jet fuel in aircraft engines.  This combustion produces water vapor that condenses into water droplets, which eventually freeze into crystals in the cold temperatures aloft.   Combustion particles aid the condensation.

Contrails are thicker when the air is already close to saturation.  Thus, contrails are particularly obvious when the air aloft is already moist.   

Look closely at the satellite imagery above, and you will see a thin veil of cirrostratus clouds, indicating air already at saturation.  Adding more water from the jet engines simply makes the clouds thicker.

Or we can look at the temperatures (red lines) and dew points (green lines) from the radiosonde (balloon-born weather observations) at Forks, on the Washington Coast (below).  Near the level at aircraft fly (marked trop on the figure), temperature and dew point are nearly the same, indicating a moist atmosphere near saturation! (the Y-axis is height in terms of pressure; 500 is about 18,000 ft, 250 is about 35,000 ft).

Temperature (°C)

Climate Change and Contrails

Contrails both cool that atmosphere (by reflecting solar radiation to space) and warm it (by emitting infrared radiation down to the ground).   

A number of careful studies have found that the warming is dominant.  

Thus, contrails contribute to global warming.  Much, much less than CO2, but still a contribution.

One way to reduce this warming by contrails is to alter flight paths to avoid cirrostratus clouds or regions where the upper troposphere (where planes fly) is near saturation with water vapor.   Some folks have suggested this be done.

In any case, the effects of contrails are relatively small, much, much smaller than the aggregate effects of global CO2 increases.

A Strong Morning Inversion Undermines Air Quality and Messes Up the Coastal Radar

This morning, a strong low-level temperature inversion caused the air quality to decline over western Washington and created false radar echoes on local weather radar.

Reminder:  an inversion occurs when temperature increases with height, a reversal (inversion) of the normal situation in which temperature decreases with height. 

Let me show what lower atmospheric temperatures looked like this morning.

At 5 AM at Forks, on the northwest Washington coast, temperatures increased by about 10°C (roughly 18°F) in the lower few thousand feet (red line is temperature).  Above the inversion, the temperature declined with height

An inversion was also present at Seattle-Tacoma Airport at 6 AM this morning, with about a 6°F warming between 400 ft and 1800 ft (see below)

Inversions create zones of strong vertical stability, inhibiting the vertical mixing of pollutants, allowing concentrations to increase near the surface.

This was quite apparent this morning as air quality declined to the moderate level (yellow colors) in the graphic from the  EPA AirNow website.

Low-level haze was apparent on the Seattle PanoCam this morning around sunrise.

Strong-level inversions can also mess up local weather radar, acting as an atmospheric lens that bends the radar beam down.  As a result, the radar beam reflects off the surface and is reflected back as a false echo, indicating precipitation where none is occurring.

Such a false echo was clearly apparent on our local coastal radar (Langley Hill, near Hoquium) at 7:21 AM.  It was not raining offshore!

Over land, spring temperature inversions weaken rapidly during the day as the land surface warms,  as illustrated by the temperatures over SeaTac at 4 PM (below).  No more inversion as temperatures at the surface warmed into the lower 70s!

So, take a deep breath...air quality is quite good now over western Washington...and I am going to go for a few-mile run knowing that bad air quality won't be a problem.