Hazy, non-perfect skies continue to plague SE Arizona

First some comparisons of clean and hazy skies so’s you’ll have some idea of what I am talkin’ about in today’s title:

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Clean day, from a few days ago.
5:19 PM. Cumulus fractus and humilis on a hazy afternoon.
5:19 PM.  Yesterday’s Cumulus fractus and humilis form in haze and smoke.  Not exactly the same view, but it was the best I could do to give you an idea of how crummy, well, to a clean fanatic,  it was yesterday
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Pretty clean day from a few days ago, looking toward Twin Peaks area during the afternoon.
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Yesterday afternoon looking toward the same area.  Note how much whiter the sky is toward the sun side of the photo.  This whiteness is due to “forward scattering” of sunlight by tiny aerosol particles.  Not much forward scattering in the prior photo.
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4:50 PM.  Yesterday’s muffin Cumulus (mediocris) over Ms. Mt. Lemmon. No aerosols can be detected in this direction where backscattering of the sun’s light occurs because the aerosols are often dark, Think about when you fly commercially and look out the window away from the sun, say, to the north, and see that ever present black haze line out there, likely the result of black carbon particles.  No ice formed in our Cumulus clouds yesterday, either.  Top temperatures too warm.

Let us see where this Arizona smog might have come from…..  Below a TEN day back trajectory plot which ends over Tucson at 5 PM AST yesterday afternoon at two levels, each below the cloud bases.  Notice in the plot below that the model data thinks the air parcels that arrived here at 1945 and 2945 meters above the ground over Tucson (bottom portion of figure) started out at the surface and went a LONG way before rising up as that air crossed Baja, the Sea of Cortez and NW Mexico.

You can see, too, that it wrapped into our upper level trough, coming down the back side, then curling around from the SW–the air in troughs and ridges moves faster than do those features themselves , and that’s also what this plot is showing you.

116891_trj001 Using a lower level end point over Tucson, ending around 3000 feet above ground level made no difference:117509_trj001

9:15 AM AST sat observations of aerosol optical depth. Blue is clean, red is awful. You can see a pile of awful air SW of us yesterday morning.
9:15 AM AST sat observations of aerosol optical depth. Blue is clean, red is awful. You can see a pretty contaminated air (red tones)  SW of us over Mexico yesterday morning, and that’s likely what moved up this way to give us our hazy skies.

So, it looks like the air may have picked up some aerosols while it stalled around over northwest Mexico before arriving here since its unlikely that the air was hazy and contained so much aerosol loading coming out of the Pacific offshore of Washington and Oregon.  No doubt it would have been out in the Pacific many days before arriving offshore of Washington and Oregon, plenty of time for deposition onto the ocean and washout one would think, leaving that bit of doubt.  And of course, this is all dependent on how accurate our back trajectory calculations are.  So, with those caveats, we can conclude that the aerosols likely came from Mexico and not the LA Basin as was mused about here yesterday.

Today’s clouds

Get cameras ready.  Should be a nice day for patterned clouds, such as Cirrocumulus, maybe some lenticulars as well since the wind remains pretty strong aloft.  Also with a minor trough coming through later today, the clouds are likely to fill in during the afternoon, and being that bit colder aloft, some of the Cu that form oughta develop a little  ice and snow virga.  That means a chance of a sprinkle somewhere in the area today.  Right now, as the sun comes up seeing some nice CIrrus castellanus, some mammatus underneath, and a few Altocumulus clouds here and there.

Still thinking about an early cold rain on Saturday morning….

The End

Author: Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.