Aura's Microwave Limb Sounder measures nitrous oxide, which is unaffected
by stratospheric chemical processes. By studying changes in its levels,
scientists can better understand how air is moving around and how ozone is
affected by that air motion, allowing them to differentiate those changes
from the ones caused by chemical ozone destruction. In these
cross-sections of nitrous oxide (top) and ozone (bottom) data from Aura,
changes in the levels of these two chemicals at various temperatures and
latitudes are depicted over time. The white contour shows the approximate
location of the polar vortex boundary.
The left panel data were collected on January 23, 2005, near the beginning
of chemical ozone destruction this winter. Virtually all chemical loss
occurred before March 10 (center panel). Ozone destruction extended
throughout the polar vortex from about 15-20 kilometers (9-13 miles), but
occurred only in the outer part of the vortex from 20-25 kilometers
(13-16 miles). The differences between the two days are depicted in the
right panel. The largest observed difference is about a 1.2 parts per
million by volume decrease in ozone. Plots of nitrous oxide show a
decrease in the region in the outer part of the vortex where most ozone
loss occurs, indicating that air from above (where nitrous oxide is lower)
has moved into this region. This downward motion brings higher ozone into
the region where chemical loss is occurring, thus partially masking the
effects of chemical loss. Calculations using Microwave Limb Sounder data
to separate dynamical and chemical effects indicate maximum chemical ozone
loss of approximately 2 parts per million by volume (approximately 60
percent) in the outer part of the vortex near 18-21 kilometers (11-13
miles), and approximately 1.5 parts per million by volume when averaged
throughout the whole vortex region.