Solar aureole photos and Asian dust

      Our local weather during March 2010 has included many cloud-free days -- ideal conditions for photographing the solar aureole. These four photos dramatically illustrate the passage over the northeastern U.S. of a large dust cloud from Asia. The photos were taken from my home at about 40°N, 75°W, using the same tripod-mounted camera and the same manual settings -- Canon PowerShot A530, ISO 80, f5.6, 1/1600s. These dust events are common farther west in the U.S., but they do not usually reach the East coast of our country.
      The photo taken on March 6 shows a very clear sky. Later in the month, photos on March 18, 19, and 20 show a dust cloud moving across this site. The captions below each image show aerosol optical thickness measured at 505 and 625 nm at the same time as the aureole photos. As expected from the photos, the AOT values in early March are very low. The large spike in AOT values coincides with the passage of the dust cloud.
      This event is also evident in the Navy Aerosol Analysis and Prediction System (NAAPS) aerosol forecast model and in NASA AERONET data from a site about 1 degrees to the north and 2 degrees to the east of this location. The Asian origin of this dust is clear from watching the NAAPS global film loops.

March 6, 2010, 11:03 EST AOT at 505 and 625 nm: 0.043, 0.029	March 18, 2010, 13:32 EDT AOT at 505 and 625 nm: 0.079, 0.056
March 19, 2010, 12:25 EDT AOT at 505 and 625 nm: 0.361, 0.293	March 20, 2010, 12:25 EDT AOT at 505 and 625 nm: 0.108, 0.075

      These two photos show an image from the NAAPS aerosol forecast film loop and data from an AERONET station about 1 degree north and 2 degrees east of this site, on March 19. Observing the NAAPS global film loop demonstrates that these "pulses" of dust are coming from Asia.

      This figure shows grayscale density scans of the solar aureole photos done with ImageJ, a freeware image analysis program avaiable from the National Institutes of Health. One example is shown, for March 20. The shape of these density plots is related to aerosol optical depth and atmospheric turbidity.