Category Archives: Dust

Dusty sunset

In case you missed it, due to all the dust, yesterday’s sunset:

Moreover, if you go to the NWS Tucson site and the forecast for Catalinaland, you will see icons showing pretty much the same thing for today and tomorrow as is in these photos. It will be interesting to see how deep the dust gets.

Where did all that dust come from, that plume of dust that moved into Tucson and environs during the mid-afternoon?

The Mexican Sonoran Desert NE of the Gulf of Baja.

You can see rivulets of dust being raised in this visible satelllite imagery loop (this will take a LOT of band width!) if you look hard at the desert regions southwest of the AZ border.  Also check out the U of A’s loop here, but that one will soon be overwritten, so good luck, and there’s nothing I can do about it.

Below, a still from that loop for 6:30 PM AST, near the time of the photos, with the dust origin region annotated with a red circle, something I have only recently learned to to with Apple’s Preview photo viewing software.  Dang.  The plumes are oriented SW-NE.  So, a few tons of Mexican desert came across the border yesterday to make AZ that bit higher in elevation.

Also in this sat image is the horrible fire near Silver City, NM, northeast of the red circle, the one that grew so much yesterday in the wind and heat.  You can see that the smoke plume was already reaching as far as Texas by the time of this image, 6:30 PM AST!

BTW, smoke particles are, in general, much smaller than dust particles are (hundredths of microns vs. a few microns) and the color of the setting sun can be used to help tell what you are looking at as far as aerosol particles go.  Smoky sunsets tend toward orange and red; dusty ones toward yellow, as above.

The End.

Was it smog or dust? How to tell

OK, climbing down off soapbox today….just don’t read the Hockey Stick Illusion by A. W. Montford unless you want to be upset by some climate scientists pretending to be scientists when they are being something antithetical to science.  Reminds me of the 30-odd years of cloud seeding reanalysis experiences I had as a skeptic in that domain.  Oops, haven’t climbed completely down yet.  Montford should get a Pulitzer for this well documented tale, and his main protagonist, Steve McIntyre, the Rossby Medal or maybe a couple of Nobel Prizes for diligence.  Just about off “box” now….but this tale REALLY does remind me of the shenanigans that happened in cloud seeding to repeat myself again and again and again.

It got pretty hazy yesterday afternoon into the time of sunset.   This is what it looked like as the sun rotated away from the earth (hahahah).  Note the yellowish tinge of the sun.  Smog (urban, biomass smoke and hazes, are comprised of smaller aerosol particles, around a 0.01 to 0.1 microns in diameter, whereas dust particles, something that you find around the house everyday here in AZ (to quote Groucho Marx from his quiz program, “You Bet Your Life”) are generally much larger and can extend into sizes of  1-10 microns in diameter.    So, in interfering with the transmission of the incoming white sunlight, small aerosol particles in smog take out (scatter) the short wavelengths like the blueish ones) and only the longer wavelengths, the reddish ones,  giving the sun an orange or reddish hue.  Dust particles, because they are larger, and do not interfere with the short wavelengths of light coming from the as much produce a whitish yellow colored sun.   Below yesterday’s sunset is a smokey one from Cuiaba, Brazil,  during the burn season, a strawman to show a large, obvious difference.  It’s often more subtle than this, so you need to practice labeling sunsets for aerosol sizes.  Your neighbors will be impressed.

Since dust particles are larger than smoke particles, they don’t stay afloat as long as smoke particles do, though dust can still drift away from where it was generated before dissipating.  It depends on the nature of the surface dust.   In Saudi Arabia, dust was often observed without much wind due to the fine nature of the sand (see last photo from Qassim, SA–looks pretty much like pure dust whereas the Catalina sunset suggests dust with smoke due to its more orange coloring).

Factoid:   some Gobi Desert dust has impacted the West Coast of the US from time to time!

Clouds?  Well, if you looked, you saw a few low cloud shreds called Cumulus fractus (Cu fra) over the Catalinas yesterday afternoon.  Some rain fell as close as central AZ as a cold front blew by.  But only the cooler air got here.  Its 13 deg cooler here than it was yesterday at this time (4:30 AM LST), a sure sign of an air mass change and “fropa” (frontal passage).