MIL/UT/NASA,
Oct 23, 2006.
October 23, 2006 - NASA and National Oceanic and Atmospheric
Administration (NOAA) scientists report this years ozone hole in
the polar region of the Southern Hemisphere has broken records for
area and depth.
The ozone layer acts to protect life on Earth by blocking harmful
ultraviolet rays from the sun. The ozone hole is a severe
depletion of the ozone layer high above Antarctica. It is primarily
caused by human-produced compounds that release chlorine and
bromine gases in the stratosphere.
From September 21 to 30, the average area of the ozone hole was
the largest ever observed, at 10.6 million square miles, said Paul
Newman, atmospheric scientist at NASAs Goddard Space Flight
Center, Greenbelt, Md. If the stratospheric weather conditions had
been normal, the ozone hole would be expected to reach a size of
about 8.9 to 9.3 million square miles, about the surface area of
North America.
The Ozone Monitoring Instrument on NASAs Aura satellite measures
the total amount of ozone from the ground to the upper atmosphere
over the entire Antarctic continent. This instrument observed a low
value of 85 Dobson Units (DU) on Oct. 8, in a region over the East
Antarctic ice sheet. Dobson Units are a measure of ozone amounts
above a fixed point in the atmosphere. The Ozone Monitoring
Instrument was developed by the Netherlands Agency for Aerospace
Programs, Delft, The Netherlands, and the Finnish Meteorological
Institute, Helsinki, Finland.
Scientists from NOAAs Earth System Research Laboratory in Boulder,
Colo., use balloon-borne instruments to measure ozone directly over
the South Pole. By Oct. 9, the total column ozone had plunged to 93
DU from approximately 300 DU in mid-July. More importantly, nearly
all of the ozone in the layer between eight and 13 miles above the
Earths surface had been destroyed. In this critical layer, the
instrument measured a record low of only 1.2 DU., having rapidly
plunged from an average non-hole reading of 125 DU in July and
August.
These numbers mean the ozone is virtually gone in this layer of
the atmosphere, said David Hofmann, director of the Global
Monitoring Division at the NOAA Earth System Research Laboratory.
The depleted layer has an unusual vertical extent this year, so it
appears that the 2006 ozone hole will go down as a
record-setter.
Observations by Auras Microwave Limb Sounder show extremely high
levels of ozone destroying chlorine chemicals in the lower
stratosphere (approximately 12.4 miles high). These high chlorine
values covered the entire Antarctic region in mid to late
September. The high chlorine levels were accompanied by extremely
low values of ozone.