TOMS Observes Low Ozone Event in Northern Hemisphere

A NASA Goddard Space Flight Center satellite has observed the lowest value of ozone ever seen in the Northern Hemisphere since satellites first began ozone measurements in 1978. The measurement was obtained on November 30, 1999 using the Total Ozone Mapping Spectrometer (TOMS) instrument aboard NASA's Earth Probe (TOMS-EP) satellite.

"This is an extremely low measurement of ozone for the Northern Hemisphere," said Dr. Richard McPeters, Principal Investigator for Earth Probe TOMS.
The measurement showed 165 Dobson Units (DU) over the North Sea between Scotland and Norway on November 30, 1999.

The previous low value of 167 DU was observed in the same region on October 30, 1985. The lowest values of ozone in the Northern Hemisphere are typically seen in the late fall period. However, these low northern values rarely drop below 180 DU.

"A combination of stratospheric and tropospheric weather systems can occasionally create these extreme low ozone events," said Dr. Paul A. Newman of the NASA Goddard Space Flight Center. "We understand that dynamics can cause these low ozone events, but we're unsure why this event set a new record low value."

Scientists and others have a keen interest in polar ozone depletion. While this particular record low value results from a convergence of weather systems, severe depletions of ozone can result from chemical processes. The Antarctic ozone hole is an example of a large ozone loss caused by chemistry. Chemically caused Arctic ozone losses have also been observed, particularly in the Northern Hemisphere springs of 1996 and 1997.

This winter, NASA in collaboration with the European Commission, is staging the largest polar ozone campaign yet. The SAGE III Ozone Loss and Validation Experiment (SOLVE) is being conducted jointly with the European Commission sponsored Third European Stratospheric Experiment on Ozone (THESEO 2000). These collaborative campaigns will examine the processes that control polar and mid-latitude ozone levels at mid to high latitudes over the course of the Arctic winter. NASA GSFC has provided theoretical contributions, a high altitude light detection and ranging system for measuring ozone and temperature, and the operational support for some of the heavy lift balloons.

For more information about the US SOLVE and European THESEO components (including a list of participating institutions), links to the respective web sites can be located above.

TOMS-EP and airborne field programs are key parts of a global environmental effort of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice and life as a total integrated system. Goddard developed and manages the operation of the TOMS-EP for NASA's Office of Earth Science, Washington, DC. Goddard scientists and instruments are integral parts of the SOLVE campaign being conducted this winter.

The TOMS instrument measures the total number of ozone molecules between the Earth's surface and space. The measurements units are Dobson units. Dobson units are convenient thickness measurements. The total ozone value represents the physical thickness of the ozone layer if all of those overhead ozone molecules could be brought down to the Earth's surface. The global average ozone layer thickness is 300 Dobson units, which equals three millimeters or 1/8th of an inch, and while not uniform, averages the thickness of two stacked pennies.