The M-124
Ozonometers Network
Arcady
Shalamjansky
Main Geophysical
Observatory (MGO), St. Petersburg, Russia, October 2002
Instruments:
The Russian network for observing total column ozone
consists of 28 stations within Russia and 2(3) Antarctic stations, which are
equipped with filter ozonometers, model M-124.
These same instruments were used at stations in Bulgaria (3
stations), Cuba (2), Georgia (1), Latvia (1), Lithuania (1), Kazakhstan (5 ),
Tajikistan (1), Turkmenistan (2), Ukraine (4) and Vietnam (3). This report and schedule refers only to
those stations, which are calibrated with assistance from the MGO with some
degree of regularity.
The
M-124 ozonometer uses two filters to measure the total ozone amount. The filter spectral intervals have their
maximum at 302 and 326 nm each with a half-width of about 20 nm. With time, the filters could be affected by solarization and this
could be the cause of observed systematic errors.
Total
ozone is retrieved from direct sun measurements at zenith angles of 20°-70° and from blue or cloud zenith measurements at zenith angles of 20°- 85° which allows for ozone measurements at northern latitude stations,
under practically all weather conditions.
All
of the M-124 ozonometers are calibrated against the Dobson spectrophotometer
No.108, which is regularly compared with the WMO standard. Intercomparisons in Boulder (1988), Hradec Králové (1993), Kalavrita (1997) and
Hohenpaissenberg (2001) showed that the measurement-scale drift of the Dobson
No.108 did not exceed 1.0 %.
The
possibility of the filter characteristic degradation determines the special
features of the station equipment and the measurement procedure. In particular, it is necessary to carry out
the regular control of a measurement scale.Each Russian ozone station is equipped with three
ozonometers: one dedicated to continuous operation, one spare and a reserve
that is sent to the MGO for calibration.
The measurement procedure consists of the mandatory
blue or cloud zenith measurements and the direct sun measurements (when sun is
clear and the zenith angle in less than 20° 70°??).
Tables of observation results are sent from the stations to the MGO
every month
The
MGO control of measurement quality is based on:
1)
the calibration of M-124 ozonometers against
the standard every two years;
2) the monthly comparison of two ozonometers, with which any station is
equipped.
3)
the comparison of direct sun and zenith
measurements (the difference can not exceed 1-3 %);
4)
the routine control over the measurements for
revealing the "m-dependence"
which indicates change of instrument spectral characteristics
The MGO analysis is being
performed to minimise the systematical errors, which are accounts for about
90 % of the total error. At the
Russian network stations, the error of a single direct sun and zenith ozone
measurement by the M-124 ozonometer is no more than 5 %. After the MGO control and correction
procedure, the measurement error could be reduced to 3 %.
Real-time data.
The MGO also
receives real-time data each day by telegram and/or e-mail. These data are then plotted on a chart to
compare with satellite ozone measurements (NASA TOMS instrument) and with 300
mb geopotential charts (as well as 200
mb geopotential and 30 mb temperature charts).
There comparisons are intended to determine main features of total ozone
distribution and to find rough (technical) errors in the real-time data.
Telegram real-time
data can be used for the WOUDC real-time ozone maps, but are not suitable for
the data submission to the WOUDC.
Ozone data for a
publication
The MGO strongly
recommends that the WOUDC users use only the MGO quality controlled data. As a minimum requirement, the data should at
least be accompanied by comments (qualified or not qualified). It is standard
practice for the MGO to submit only qualified data to the WOUDC.
At present, the
MGO presents the qualified data only from Russia and Kazakhstan instruments.
Since 1973, the
MGO have performed the control of the filter ozonometers (models M-83 and
M-124) data for the former USSR ozone network.
The MGO also recommends that the WOUDC users do not use any M-83 data
prior to 1973 because of large systematic errors.
State of the M-124
ozonometers network (as of 2002)
The M-124
ozonometers have been in operation for more than 17 years. Each ozonometer requires regular maintenance
and repair. With assistance from the
WMO, a number of M-124 instruments have been upgraded. Such upgrades include the installation of an
inner power supply block, block of thermostabilization and a complete set of
new optical filters.
Filter updating is
a challenge for the MGO now because Russian industry does not manufacture
inexpensive optical glasses anymore.
Up to the year
2002, the MGO upgraded two thirds of the Russian ozonometers.
The instruments
located in Lithuania (1 station) and Vietnam (4) were upgraded and calibrated
at the MGO in 2002. Also in 2002, two ozonemeters were prepared for Cuba.
The Bulgarian
ozonometers were calibrated in 2000.
The Ukraine (3)
and Kazakhstan (4) ozonometers were partially upgraded and then calibrated in
1999.
The Latvian
ozonometer was calibrated in 1997.
The Georgia,
Turkmenistan and Tajikistan instruments have not been calibrated since 1995-96.