Strange lines over the northeast Pacific

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The visible satellite imagery over the northeast Pacific Ocean looks very strange today, with weird-looking lines and strange shapes in the clouds.  Take a look at image from 11:15 AM this morning from the National Weather Service GOES weather satellite:


You can also see the low clouds over Willamette Valley and the snow in the Sierra Mountains, as well as those infernal lines over the Pacific.  You can get another view of these clouds from the high-resolution MODIS satellite:


What are these lines?   They are commonly called ship track clouds and are produced by the particles emitted by ships that burn oil, diesel, or coal.    We often see ship tracks in the late spring and early summer, but they are fairly unusual this time of the year...and I will tell you why.

Right now, we have a BIG ridge of high pressure over the eastern Pacific, more like a summer pattern than a midwinter situation.  Here is the surface map at 10 AM to illustrate:

With high pressure we don't have storms or fronts, and certainly none of the clouds associated with them, since high pressure is associated with sinking air.   Sinking air produces a stable situation, often with an inversion (a zone of increasing temperature with height) above a shallow marine air.   Without a lot of mixing from the strong winds of storms, this shallow marine air layer gets saturated (it is in contact with the ocean!), with lots of thin stratus and stratocumulus clouds.

But where do the ships come in?  It turns out that Pacific air is relatively clean, often with only 10-20 particles per cubic centimeter.   Cloud droplets form on this particles and thus over the ocean we tend to have relatively few cloud droplets (but bigger ones) in some volume of air.  But combustion from ships produces lots of particles and can increase the numbers to hundreds per cubic centimeter (see graphic).  That results in a lot more cloud particles, but smaller ones.
Having a lot more particles, but smaller ones, reduces the ability of the clouds to precipitate, so the clouds last longer.  And it turns out that clouds with more small particles reflect much more of the sun's light, appearing brighter.    That is the origin of the ship tracks...the pollution of the ships enhancing the clouds and making them brighter.  The ship tracks tend to get wider downstream of the ship as the combustion particles mix into the environment.

We can look at super high resolution MODIS imagery and can almost see the ships.  Here is an example:


The U.S. Navy was very concerned about ship tracks during the cold war, since it was a way the Russians could spot our non-nuclear ships.  

Now could we use ship tracks to combat global warming?  Some people have suggested we do so.   Ship tracks produce clouds that reflect more of the solar radiation back to space (that is why they are whiter!) and thus help cool the earth.   So lets produce many more ship tracks...but we want to do it without burning fossil fuels.   To do so, it has been suggested we build a fleet of giant ships that inject salt water droplets into the atmosphere--the water would evaporate, leaving huge numbers of salt particles to waft into the atmosphere (see picture).   The result, a huge amount of particles and a lot more cloud droplets...super ship tracks and perhaps a bit cooler climate.