Aerosols, Cumulus clouds, Definitions, Fog, Stratocumulus clouds

A study in fog and smog

While yesterday did not have the drama of the prior few days, there was aerosol drama anyway, a real battle took place against the forces of evil, represented by air loaded with urban smog, and good, clean air to its north, in which we were initially immersed.

A rare fog bank streamed out of Tucson toward Marana, Continental Ranch, and south Oro Valley and beyond. The moist air near the ground associated with our recent deluge, and capped by an inversion, combined with very light winds allowed fog to form in the first place. Its westward trajectory into the southern reaches of Oro Valley is associated with the normal sloshing of winds in Tucson, from southeast in the morning, to northwest in the afternoon on “undisturbed” days. On most mornings, all we see is a haze layer close to the ground that streaming out of Tucson down that way. In this case, the smog layer was in the form of fog, droplets wreaking with all kinds of untoward particles and chemicals like sulfates, nitrous oxides, hydrocarbons, etc., these from cars, wood burning stoves, factories, etc, all the things associated with modern life in an urban center except for wood burning stoves. As a smog-containing fog, it was pretty, however.

However, most of the time, maybe nine out of ten, that thin smog layer stays south of Catalina, can’t quite get here. But yesterday, the forces of evil resulted in an advance of the smog-fog to Catalina. A southwest wind came up in mid-morning, and like a tidal wave, that low thin layer slurped its way up the Catalina Mountain sides and Oro Valley, rolling over everything, growing deeper as the long absent sun warmed the ground, dissipating the fog, leaving the aerosol contained in it, “naked”, as it were.

It seemed for a time that a slight north wind might rule the day, and the smog would stay south of us as it usually does.  Instead an ugly southwest wind developed, as often happens here in the afternoon, as air starts rising off the Catalinas to form Cumulus clouds.

And that’s part of what happened yesterday to bring us smog, besides us being in the protected lee of the Catalinas due to northeast winds aloft.  When you’re in the lee, sometimes moisture and aerosols remain trapped there, like those cattails I used to pop open at the north entrance of the University of Washington’s Atmospheric Science Department on days with a strong southwest wind and those seeds would circulate in the lee for maybe an hour in really interesting swirls that could be seen due to all the seeds floating around and around, incoming people waving their arms to get them away because they would stick on your clothes.  I was younger then (40s maybe), and I guess it was pretty childish.  I’m not like that today, as demonstrated by this blog.  I wish I had some cattails today, though.

7:04 AM. Fog streams westward from TUS.
7:04 AM. Fog streams westward from TUS.
7:06 AM. Close up of "sfog" bank. Looks pretty outside, but its not inside.
7:06 AM. Close up of “sfog” bank. Looks pretty outside, but its not inside.  There are people like that, too.
7:27 AM. Another close up, almost surreal looking with Kitt Peak in the background.
7:27 AM. Another close up, almost surreal looking with Kitt Peak Obsy in the background.
7:35 AM. If you ever need to get warm, popping up out of the fog and Stratus is a turret due to a heat source over there maybe off Tangerine Road, I-10 area.
7:35 AM. If you ever need to get warm, popping up out of the fog and Stratus is a turret due to a heat source over there maybe off Tangerine Road, I-10 area.
7:57 AM. It seemed to be a little closer..... Hmmmm.
7:57 AM. It seemed to be a little closer….. Hmmmm.
9:44 AM. NO doubt about it, its creeping on cat's feet toward Catalina! I have never taken so many photos of fog before, too. You could see trees and other prominences disappearing as it came closer.
9:44 AM. NO doubt about it, its creeping on cat’s feet toward Catalina! I have never taken so many photos of fog before, too. You could see trees and other prominences disappearing as this smog-laden fog came closer.
10:54 AM. The warming air had dissipated the leading edge of the fog coming toward Catalina, but now the the invading smog with it was revealed for all to see.
10:54 AM. The warming air had dissipated the leading edge of the fog, leaving only shreds of Stratus fractus clouds that were coming toward Catalina.  But now the the invading smog with it was revealed for all to see, that hazy layer below those clouds along the mountains.
11:35 AM. The smog was reaching Catalina, the smog front advancing here along the side of Samaniego Ridge
11:35 AM. The smog was reaching Catalina, the smog front advancing here along the side of Samaniego Ridge, with almost a little arcus-like Cumulus cloud marking its advance (left of center).  It was a profoundly disturbing moment that what seemed like it was going to be a visually pristine day, was now going to be mucked up by some Tucson smog.
12:35 PM. Got pretty bad down there by Pusch Ridge, before more heating mixed it up into Cumulus and Stratocumulus clouds topping the Catalinas.
12:35 PM. Got pretty bad down there by Pusch Ridge, before more heating mixed it up into Cumulus and Stratocumulus clouds topping the Catalinas.
Also at 12:35 PM, but looking north into the pristine air that was to the north of the smog bank. This was not clearer looking just due to not seeing aerosols in the backscattering view. The prior pictures call out areas of smog due to "forward scattering" of the sun's light toward you.
Also at 12:35 PM, but looking north into the pristine air that was to the north of the smog bank. This was not clearer looking just due to not seeing aerosols in the back scattering view in which itgs much tougher to see aerosols–they’ll look dark or brown. not whitish. The prior pictures call out areas of smog due to “forward scattering” of the sun’s light toward you by the aerosol particles.

 

5:24 PM. The sun set amidst the smog and so the light on the mountains had a slightly more orange look. It was still pretty the way the scene was framed by Stratocumulus clouds.
5:24 PM. The sun set amidst the smog and so the light on the mountains had a slightly more orange look. It was still pretty the way the scene was framed by Stratocumulus clouds.
5:55 PM. The sun sets amidst a well-loaded aerosol layer, looking orangy-red, and producing the reddish orange cloud base highlights in a polluted Stratocumulus layer.
5:55 PM. The sun sets amidst a well-loaded aerosol layer, looking orangy-red, and producing the reddish orange cloud base in a polluted Stratocumulus layer.  The yellowish orange sky below cloud base, with faint undulations in it,  shows that a smog layer is present, and, if you look closely toward the Tucson Mountains at left, you will see the top of the smog layer is becoming visible as an inversion forms, trapping it once again.

No rain in sight.

The End.