| The Match method quantifies chemical ozone loss in the polar stratosphere.
The basic idea consists in calculating the forward trajectory of an air parcel
that has been probed by an ozone measurement (e.g., by an ozonesonde or
satellite instrument) and finding a second ozone measurement close to this
trajectory.
Such an event is called a "match".
A rate of chemical ozone destruction can be obtained by a statistical analysis
of several tens of such match events.
Information on the uncertainty of the calculated rate can be inferred from the
scatter of the ozone mixing ratio difference (second measurement minus first
measurement) associated with individual matches.
A standard analysis would assume that the errors of these differences are
statistically independent.
However, this assumption may be violated because different matches can share a
common ozone measurement, so that the errors associated with these
match events become statistically dependent.
Taking this effect into account, we present an analysis of the uncertainty
of the final Match result.
It has been applied to Match data from the Arctic winters 1995, 1996, 2000, and
2003.
For these ozonesonde Match studies the effect of the error correlation on the
uncertainty estimates is rather small:
compared to a standard error analysis, the uncertainty estimates increase by
15% on average.
However, the effect may be more pronounced for typical satellite Match analyses:
for an Antarctic satellite Match study (2003), the uncertainty estimates
increase by 60% on average.
The analysis showed that the random errors of the ozone measurements and the
"net match errors", which result from a displacement of the second ozone
measurement of a match from the required
position, are of similar magnitude.
This demonstrates that the criteria for accepting a match (maximum trajectory
duration, match radius, spread of trajectory clusters etc.) ensure that, given
the unavoidable ozone-measurement errors, the magnitude of the net match errors
is adequate.
The estimate of the random errors of the ozonesonde measurements agrees well
with laboratory results. |