Nov 20, 1994 - the ozone data during the first decade was unsatisfactory. After 1972 an ... the first version of the ozonometer type M-83 records about 6%.
3OURNAL OF GEOPHYSICAL RESEARCH, VOL. 99, NO. Dll, PAGES 22,985-22,999,NOVEMBER 20, 1994
Total ozone changesover Eurasia since1973 based on reevaluated
filter ozonometer
data
Rumen D.Bojkov andVitaliE.Fioletov • AtmosphericEnvironmentService,Downsview,Ontario,Canada
ArcadyM. Shalamjansky Main GeophysicalObservatory,St. Petersburg,Russia
Abstract. Sincethe early 1960s,on the vastterritoryof the former USSR, 45 stationshave beenin continuousoperation,utilizing the broadbandfilter M-83 ozonometer.The quality of the ozonedata during the first decadewas unsatisfactory.After 1972 an improvedversionof the ozonometerwas introducedtogetherwith improvedquality controlpractices,including methodologyof observations. The morereliabledataof 1973 throughMarch 1994havebeen rigorouslyreexaminedby applyingvariabilityanalysis,comparisonwith lower-stratosphere temperatures and/ornearbyDobsonstations,andoverpassing TOMS for identifying concurrenceor discrepancies. Thesecontrolprocedures togetherwith the informationon instrumentrelocationandcalibrationsmadeit possibleto reevaluatethe recordof all 45 stations.The accuracyof the improvedozonometerdatais about3% for directSun measurementsand •-5% for zenith sky observations;althoughnot so goodas that of the Dobson,in the long run it providesconsistentozonedata sets.This data setis now made available to the World Ozone Data Center (WO3DC), Toronto. Thus for the first time, basedon a 21-year long record,informationis deducedon the differencesin the ozoneannualcycle betweenEasternSiberiaandthe Europeanpart, on the strongappearanceof quasi-biennial oscillation(QBO) signalsespeciallypronouncedasozonedeficiencyduringthe westernphase of the QBO, on the ozonevariability, and on the long-termchangesover the huge territory from CentralEuropeto the Far East.The specificsof the ozonechangesconsideredin concurrence with the prevailinggeneralstratospheric circulationconditionspermittedus to distinguishfour broadregionswith consistentozoneregimes.The appearanceof the strongestnorthern hemisphereozonemaximum and a monthlymeanof-470 matm cm over Siberiaduring winter-spring,comparedwith -400 matm cm overEurope,the occurrenceof the ozoneannual minimumsas early asAugustoverEasternSiberia,comparedwith Octoberover the European part, was establishedandis probablyrelated'tothe specificsof the atmosphericcirculation patterns.The long-termozonechangesare consideredin relationto the stratospheric temperatureat 100-hPa.For eachdeviationfrom the monthlynormaltemperatureby 1øC, there is a corresponding changeby the samesign5-6 matmcm in the monthlyozonedeviations.The calculatedlong-termozonetrendsfor 1973 throughMarch 1994 (givenin percentper decade +2c•)are asfollows:Europeanpart,-3.6_+0.8;CentralAsia,-2.0+0.6; WesternSiberia, -3.5+0.8; and EasternSiberia - Far East, -3.2_+0.8.They showa steadyozonedeclinesimilarto that deducedfrom the Dobsonstationsat the samelatitudes.The declineduringthe past 15 yearsis strongerand,in general,concurswith Total OzoneMappingSpectrometer (TOMS) trendswhich are, however,slightlymore negative. 1. Introduction
surfaceof the northernhemisphere.Shortcoming due to the very broadband(>40 nm) filters originally used, resultingfrom the Filter-ozonometeris used continuouslyin about one third of shiftingof theeffectivewavelengths by up to 8 nm for the usual the Global Ozone ObservingSystem(GO3OS) stations,nearly Sunzenithanglevariations,were revealed25 yearsago[Bojkov, exclusivelyin the former USSR countriesfor the last 30 years. 1969a;Bojkov, 1969b]. It was shownthat even on sunnydays More than 45 stationswere establishedto provide information the first versionof the ozonometer typeM-83 recordsabout6% on the total ozone characteristics over about a third of the land less ozonethan the Dobsonspectrophotometer for observations taken at Sun zenith angles40ø). In the presence of high atmospheric turbiditythe M-83 readingswere another5 to 10% higherthan Papernumber94JD02006. 0148-0227/94/94JD-02006505.00 thoseof Dobson.These findingsas well as later analyses[e.g., 22,985
22,986
BOIKOV ET AL.: TOTAL OZONE CHANGES OVER EURASIA
Bessonovet al., 1971; Basher, 1977; Michalowska-Smak, 1981;
Romashkina,1985] suggestthatthe datafrom the first versionof M~83 in use until 1972 [Gustin, 1963; 1969], had extremely high variability, were noisy,inconsistent,andpracticallyuseless in the studyof long-termozonechanges. To improve the quality of the M~83 data, all network ozonometershave, since 1969, been calibrated against the Dobson108 at Feodosiain the sunnyconditionsof Crimea and later in the Main Geophysical Observatory (MGO) in St. Petersburg [Romashkina,1985]. In accordancewith the recommendationsmade by Bojkov [1969a], a more accurate nomogram,taking into considerationthe influenceof variable "effectiveozoneabsorptioncoefficients"as a functionof It and totalozone,was developed.A third filter wasutilized as well, in order to take care of the aerosol effect [Gustin, 1970].
Furthermore,sincelate 1971, a new versionof the M~83, having narrower band filters (half transmissionband 21 and 15 nm, with a maximum spectralsensitivityat 299 and 325 nm) was introducedandby the end of 1972 the renovationof the network was completed.The wavelengthdifference between the two filters was reducedwhich nearlyeliminatedthe need for aerosol correctionsand two extra filters with maximal sensitivityat 369 and
530
nm
were
used
for
the
determination
of
aerosol
extinctions [Gustin, 1969; Gustin et al., 1976]. As shownin the
present study, these measureshave collectively resulted in substantialimprovementsin the performanceof the M~83 filter-ozonometerafter 1972. Intercomparisonscarried out at WallopsIslandduring 1980 [Parsonset al., 1982] indicatedthat althoughthe accuracyof a single M~83 measurementis lower than the Dobson's the daily averages tend to improve its agreementwith Dobson.The zenith sky measurements did show a very high discrepancyin single days due to the use of an imperfectzenith-Sunnomogramreplacedsinceby MGO. During the early 1980s, improvementsin the electronicsand the optics of the ozonometerled to the developmentof the M~124 version of the filter-ozonometer [Sokolenko, 1983; Gustin and Sokolenko, 1984; Gustin et al., 1985; Dudko et al., 1985] which
was
introduced
in
the
former
USSR
network
in
1984-1986. Althoughthis instrumenthas the samefilters as the improvedM~83, it hasa reflectordirectingthe solarbeamon the instrument,its filters are in vacuumcapsuleswith temperature measured for correction, and the relative errors reported for well-kept instrumentshave an accuracyof slightly better than 3% for direct Sun and -5% for zenith sky observations[Gustin
Thus the recordswere thoroughlyreevaluatedand were usedto derive for the first time detailed characteristics of atmospheric ozoneovera hugepartof thenorthernhemisphere (fromEastern Europeto the Far East). Statisticallysignificantnegativetrendsof 2 to 5 % perdecade
(depending on the season)were estimated.One shouldrecall that in the northernhemispherethe winter-springseasonsof 1992 and 1993 were with extremelylow total ozone;however, the
winter
of
1993-1994
was
closer
to
normal.
These
fluctuationsinfluencedthe trend calculationsresultingin about
a 0.5% stronger year-round declinewhichhoweveris withinthe 1• limit. The ozone trends for a different time interval (e.g., 1979-1994)arecomparedwith TOMS andshowgoodagreement and showthat the ozonedeclinewas strongerduringthe last 15
years.Detectedis evidenceof the quasi-biennialoscillation (QBO) influenceappearingas a pronounced ozonedeficiency abouthalf a year after the sharpeasterlywind maximumand continuing duringmostof thetimewhenwesterlywindsprevail in the equatorialstratosphere at 50~hPa.The existence of a big regionwith a springozonemaximumoverEasternSiberia-Far East, whichis nearly 15% higherthan the otherknownspring ozone maximums over the same latitudes in Canada, and the
appearances of substantialdifferencesin the annualcourses betweenEuropeandEasternSiberia~ Far Eastwereconfirmed. Thus this paper providesinformationbased on reevaluated ozonedata unavailableto date for this hugepart of the northern hemisphereand particularly for the internationalozone assessments.
2. Data Availability, Its Quality, and Reevaluation Figure1 showsthe locationsof 45 filter-ozonometer stations and the closestDobsonstations(numbersare given accordingto the WMO World Ozone Data Center (WO3DC) identifiers). Observationsfrom all of these stationswere publishedin the former USSR every one to two years [e.g., Gidrometeoizdat, 1978], but before 1989, data from only 20 stations were submittedto WO3DC regularly.Since 1989, in a few steps,all data were made available to the WO3DC and the thoroughly
reevaluateddata preparedfor and usedin this studywerejust deposited as a serviceto the ozonecommunity. Althoughall of the stations were operating continuously (except the Skovorodino station that was closed in 1979), some data were
omitted in the publicationsfor their low quality and/or infrequentnumberof observations (see Table 1). For these et al., 1984; Gustin et al., 1985; Govorushin et al., 1985]. reasons some stations have only limited years of useful In view of the increased interest in the behavior of for the trend determinationpart of this studyand atmosphericozone and some very specific features appearing observations they are indicated with an asteriskin Table 1. For the long-term over the hugeterritoriesof the former USSR as well as to assure variation's analysisand trend estimationsthe stationswere quality input to the World MeteorologicalOrganization(WMO) in accordance with theirozoneregimeintofourregions, ozone assessments,it was deemed necessaryto evaluate the grouped performanceof the improvedM-83 (and M-124) in operationfor which are shown in Figure 1. Becauseof the lack of data coveragefor all seasonsin the polar region (stationslocated the last 21 years at all filter stations. Some provisional filter data were used by Stolarski et al. [1992], but informationon north64ø) the trend analysisof thesedata is performedonly for periodandcomments are not soextensive instrumentperformance,its replacementat the stations,and theMarch-September calibrations, although reported at the Quadrennial Ozone as for the other self-containedregions. On Figure2, asan exampleof theentire30-yearrecord,plots Symposiumsin 1988 (by Bojkov) and 1992 (by Bojkov and Fioletov),becamepublicly availablethroughthe WO3DC only the total ozonemonthlydeviationsfrom their long-termmonthly now. The recordswere comparedwith the few nearbyDobson mean normalizedby dividing them in the respectivemonth stations,or with filter stationsof the sameregionas well as with standarddeviation.The two stationsare typical for the middle overpassing TOMS satellite.Furthermore,the long-termozone latitudes (Moscow, 56øN) and for Central Asia (Dushanbe, variationswere analyzedin concurrencewith thoseof the lower 39øN).They showa very highvariabilityin the earlieryearsand stratospheric temperatures. These steps of the analysis a relativestabilityof the revisedM~83/124dataafter 1972.The andthe changeof the national collectively permitted the flagging of discrepanciesand changein calibrationprocedures considerationof someof the effectsof stratospheric circulation. standard to Dobson 108 since 1969 have resulted in a dramatic
BOJKOV ET AL.: TOTAL
80 ø
OZONE
CHANGES
70 ø
OVER EURASIA
70o
22,987
S0ø
%114
.%
,1•50
/
%%
Figure 1. Locationsof the filter stationsare notedwith their WO3DC numbers.The stationsindicatedby squaresand their initials are equippedwith Dobsons.The dottedcurvesshowthe four regionswith similar ozoneregimesdiscussed in the text. All stationspolewardfrom 64øNoffer limited data coverageduringthe winter.
shift in the averageozonelevel. Before 1969 it is obviousthat the level of calibrations
was such that the instruments
were
were not free from methodologicalerrors. During the present analysis it was detected that before 1979, results of zenith measurementsfor the middle- and high-latitudestationswere giving ozone values by-5% higher than the direct Sun measurements.Figure 4 shows the long-term ozone variations for the Europeanpart of the former USSR from direct Sun and only zenith sky observationssmoothedby 1-yearrunningmean.
reading,on average,very low ozone.In this early period,MGO was using Dobson 9 as a calibrationstandardwhich was with measurements only of the C wavelengthpair whichgives-7.5% very low'ozonevaluescomparedwith thosecommonlyusedin the GO3OS Dobson-AD wavelengthpairs. From 1969 to 1972, although the high variability exposedby the first version of Because of the correlation between total ozone and weather M-83 continues,at least the average ozone level seemsto be condition, direct sun measurementsare systematicallylower closerto reality. Data variabilitydrasticallydecreasedafter 1972 than zenith sky observationsby 2%. This bias was removedin (from about50 down to 15-20 matmcm of the monthlymeans). the preparation of Figure 4 in order to make clear the difference between direct Sun and zenith Credit for this belongs to the introductionof the narrowband instrumental observations. filters which moved to the shorterwavelengthfrom effective %=319 down to 309 nm and to better methodologyfor After 1980 the differencebetweenthe two data setsin Figure consideringthe effective ozone absorptioncoefficientsas a 4 is small (-1%), thanksto the introductionof a correcttransfer function of the ozone air mass and for observations mentioned diagram. It is also small in 1973 becausein this year, zenith above. measurementswere made only at MGO, where the Dobson Figure 3 showsthe overall characteristics of the ozonedata at instrument was available to check and transfer the Sun data to M-83 stations beforeandafter1972,compared' with thoseof zenith data. In 1974-1979 the differenceis however significant Dobson'slocatednearbyin the samegeographic region.The top (-5%). The situation is the same in the other regions. The panel showsthe averagedifferencebetweenthe meanmonthly comparisonwith the nearestDobson stationsas well as lately valuesof sevenpairs of M-83 and the Dobsonstations.Before with TOMS shows that direct Sun measurements are correct. 1972 the M-83 were reportingmore than 8% very low ozone Further studies at MGO indicated a need for an improved valuesin summer,when observations are usuallytakenat high zenith-Sun transfer diagram which was indeed introducedin Suni.e., low zenithangle,andmorethan9% veryhighvaluesin 1978. For these reasons, zenith data for 1974-1979 were October-March,whenobservations areusuallytakenat low Sun, downward correctedby 5%. However, since not all stations i.e., high zenith angle. The bottompanel showsa decreaseof introducedthe new nomogramsimultaneously, the differencein relative variability by 2.4 times, which is a sureindicatorof the Figure 4 is not always 5%. improved performanceof M-83 after 1972. Dobson's relative Unlike Dobson stations, a filter instrument station usually variability (i.e., the average monthly standard deviations uses two or three ozonometers.The commonpractice at these expressedaspercentof the monthlymean)beforeand after 1972 stationshas been that approximatelyevery 2 years, one of the is the same. The annual courseof higher winter and lower ozonometersis replaced. A new instrument calibrated by summervariability shownby bothDobsonand M-83 after 1972 Dobson 108 at a central location (between 1969 and 1978 at is whatonewould expectfrom a goodsetof data. Feodosia,after 1978 at St. Petersburg)is deliveredto the station Although the quality of the filter instrumentdata became and one of the old instrumentsis sent to MGO, St. Petersburg. much better after 1972, in 1970s the ozonometer observations The two instrumentsdid work parallel for 1-2 weeks and then
22,988
BOJKOV ET AL.' TOTAL OZONE CHANGES OVER EURASIA Table 1. List of StationLocationsand PeriodsWith ReevaluatedOzone Data (Black Dashes) Station
Lat
Long 73
75
77
79
81
83
85
87
89
91
93
%
76.93
003
Alma-Ata
43.23
005
Dikson
73.50
80.23
016
Vladivostok
43.12
131.90
033
Abastumani
41.75
42.83
042
St. Petersburg
59.97
30.30
...........................................
Irkutsk
52.27
104.35
..... •'
086
Feodosia
45.03
35.38
....................................
087
Kiev
50.40
30.45
•••"•
090
Ashkhabad
37.97
58.33
..........................................
112
BolshayaElan
46.92
142.73
.........................
113
Dushanbe
38.58
68.78
..........................
94
114
Heiss Island
80.62
58.05
.....................................................................
26
115
Samara
53.25
50.45
..........................
87
116
Moscow
55.75
37.57
......................
94
117
Murmansk
68.97
33.05
........................
73
118
Nagaevo
59.58
150.78
....................................
119
Odessa
46.48
30.63
..............................
120
Omsk
54.93
73.40
...................................
8O
121 122
Riga Ekaterinburg
56.97 56.80
24.07
.........................................
62
60.63
............................
85
123
Yakutsk
62.08
129.75
............................
77
128
Karaganda
49.80
73.13
..............................
87
129
Pechora
65.12
57.10
............................
74
130 142 143
Petropavlovsk 52.97 Igarka * 67.47 Krasnoyarsk 56.00
158.75
............................
87
86.57
.........................................................
37
92.88
.........................
91
144
Markovo
64.68
170.42
......................................
145
Olenek
68.50
112.43
............................................
147
Semipalatinsk
50.35
80.25
.................................................
52
148
Vitim
59.45
112.58
..........................................................
36
150
Hanty-Mansijsk 60.97
69.07
....................................................
39
153
Voronez
51.70
39.17
............................
87
182
Aralskoe More
46.78
61.67
...................................
78 81
*
---
....
76
085
*
.......................
64 ---•
77
..................
92
•'••
67 •'
92
71
•'••
79
56 •'
............
35
183
Gurev
47.02
51.85
.................................
184
Lwow
49.82
23.95
..................................
80
185
Tbilisi
41.68
44.95
........................................
67
128.92 40.50
.................................................................
24
..............................
67
186
Tiksi
71.58
271 272 273
Arkhangelsk Volgograd Kotelnyj
64.58 48.58 76.00
274
Nikolaevsk
* *
53.15
45.72
.............................................
137.90
..........................................................................
---
....................
28
16
140.70
............................................
63
275
Skovorodino
54.00
123.97
.....................................................................
25
276
Tufa
64.17
100.07
......................................................
277
Cimlansk
47.73
42.25
..................................
38 79
278
Cardzou
39.08
63.60
..............................
*
•-•m•
80
Eachdot indicates3 monthsof missingor rejecteddata.The lastcolumngivespercentage of availabledata.The World Ozone Data Centeridentificationnumberof eachstationis in the first column.Asterisksdenotelimited yearsof observations.
only the new instrument is used for the measurements.This practicepreventsestablishing a station-instrument historywhich is so helpful for tracingthe quality performanceof any Dobson station. Each instrumenthas its own systematicerrors. The relatively short period of intercomparisonbetweenthe old and the new instruments, and possible random errors of measurements for this period, makesdifficult the detectionof systematic errors of less than 2%. The complete list of instrumentsand periods of their operation is submitted to WO3DC for publicationin the catalogof ozonestationsand of ozone data for 1985-1993.
The common practice in the MGO ozone center was to analyze the differencebetween old and new instrumentsthat
wasa basefor the dataquality control.If thisdifferencewas less than 5%, the data were submittedto WO3DC as they were; if it was grater than 10%, the data were discarded,and for the interval 5-10% the data were corrected.Unfortunately,the time interval for the correctionwas not always defined properly. In general,it was possibleto get the intercomparison information
onlyafterthe old instrument replacement, sometimes in 2 years. That is why somedata were originallysubmittedto the WO3DC for publicationbut discardedor corrected in the later Sovietdata publications. For data quality control also the results of intercomparisons of direct Sun and zenith sky observationsas well as comparisonwith the neareststationdatawere used. The entire filter-ozonometerdata set on requestby WMO
BOJKOV ET AL.: TOTAL OZONE CHANGES OVER EURASIA
20 % o
-20
MOSCOW (56øN,38øE) 20
o
22,989
179 in September1988. The intercomparison of the 128 and 179 instrumentshas shown that the 128 data was 8% too high. For the WO3DC publication the data of this instrument were decreased by 8% for the period from February 1988 to September 1988 and by 4% for January 1988, but the comparisonwith TOMS showsthat the whole periodfrom July 1986 onwardrequiresthe samecorrection.The bottompanel of Figure5 showsthe resultof the appliedcorrections. Comparisonof the reevaluateddaily mean values with the overpassingTOMS, for example, with the stations in the Europeanpart of the former USSR during the 1979-1991 period (>22,000 pairs) showsthat the averageof the differenceis 0.6% and its standarddeviationis 4.5%. For the days with direct Sun observationsthe averageof the differenceis the same, only the standard deviation is smaller (-4%). About 76% of all differences
are
within
one
standard
deviation
interval.
For
comparisonthe standarddeviationsof the differencesbetween TOMS overpasseswith the Central Europeanstationsequipped -2o with Dobson instruments a is 3.5% (2.7% for direct Sun measurements)and slightly more than 80% of the compared pairs are within one standarddeviationinterval. -4o Another criterion for the data quality control is the comparisonof deseasonalized and normalizedtotal ozonevalues with similarly treated data of 100-hPa temperaturefrom the 1960 1970 1980 1990 daily radiosoundingsat the same stations. The correlation Figure 2. Monthly ozone deviations(in percentt¾omtheir betweentheseparametersis relatively high in the middle and "normal" values for the period 1973-1990) at two stations high latitudes(up to 0.8) and it is causedby physicalprocesses, locatedat 56øand39øN. Theyshowveryhighvariabilityduring mainly due to vertical and horizontal transport in the lower as well asradiativeeffects,as discussedin detail by the first 10 yearsof usingvery broadbandM-83 instrumentand stratosphere impropercalibrationsand relative stabilityof the revisedseries Godson [1960], Bojkov [1988], Randel and Cobb [1994], and addressedagain in section4 below. For the data quality control after the introduction of new instrument and methods of
DUSHANBE (39øN, 69øE)
I
i
i
observation improvements sincethe early 1970s. Before
startedto be reevaluatedin 1990-1991in a joint effort by scientists of the MGO andthe CentralAerological Observatory (CAO) under guidanceprovidedby WMO. For this review, all suspected data were identified on the basis of instrument calibrations and "old-new" comparisons. Furthermore, intercomparisonwith nearestozonestationdata was used,with stratospheric temperatureat 100-hPaand with TOMS (version 6) in a mannerdescribedin chapter3 of the Handbookfor Total OzoneData Reevaluation[WorldMeteorologicalOrganization [WMO), 1993]. The corrections introducedwere mainlybased on "old and new" instrument intercomparisons.TOMS data were used mostly for identificationof discrepanciesand for preciseestimationof the time intervalswith uniformsystematic
1972
_
+--+-q__q.
o
After 1972 -+..+. N
-5-
I
I
&, Before 1972
10-
errors.
As an example, Figure 5 showsthe resultsof the correctionof
1
Dushanbestationdata. The differenceof the originaldata, as they were depositedto WO3DC, versusTOMS data is shownin the top panel.The M-83 instrument90 operatedfrom August I I I I I I I I I I I I 1980 to July 1984 had g-dependentand systematic errors.The g-dependencewas approximated with a sine function and JAN MAR MAY JUL SEP NOV subtracted.The systematicerror was detectedin 1984 from the intercomparison with instruments 142 (operatedfrom Augustto Figure 3. (Top) Average differencesof the filter ozonometer October 1984) and 61 and the correctionwas introducedbefore
thesubmission of thedatato WO3DCbut onlyfor 1984.Later,a slight correctionwas applied to instruments142 and 90 and thesecorrecteddata appearedin the Soviet data publication. From July 1985 to May 1986, instrument90 was used, but its datahadlow qualityandwererejected.For theperiodfromJune 1986, M- 124 instrument128 wasusedwhichwasreplacedwith
versus nearby Dobson stations. Before 1972 (very broadband M-83), triangles show strongg-dependence(annual amplitude of >17%) and an obvious improvement thereafter (pluses). (Bottom) Relative variability decreaseby 2.4 times as result of a seriesof instrumentand methodologyimprovementsafter 1972. The Dobson (diamonds)relative variability remainsnearly the samefor both periods.
22,990
BOIKOV ET AL.' TOTAL OZONE CHANGES OVER EURASIA
% 8
result, different seasonalbehaviorof total ozone(see Figure 7). The monthly mean values (calculated as an averageof the station'smeansfor the givenmonth)andstandarddeviations(o) typical for stationsof each region are providedfor reference purposesin Table 2. In the Europeanpart of the formerUSSR, very similarto the EuropeanDobsonstationsthe annualmeanis about
-4
•--
-8
............ ZENITH(CORRECTED)
....... I
975
SU_N
ZENITH I
1980
I
1985
I
1990
1995
Figure 4. Long-termcourseof ozonedeviationsfrom the 1973 to 1990 "norms"over the Europeanpart of the former USSR derived by observationstaken at direct Sun (continuousline) and only at zenith sky (dashedline) smoothedby a 12-month runningmean. Note the ~5% differencebefore 1979. After new zenith-Suntransferdiagramswere introducedthe differenceis minimized.The correctedversionof zenithdata are plottedby a
350
matmcm
and
the
maximum
is
reached
in
March-April followedby a steepdeclinetill October-November. Very different from that is the annual coursein the Eastern Siberia - Far East region (annual mean ~390 matmcm) where pronounced minimumoccursin Augustanda maximumof about 470 matmcm in February-March.Western Siberia with an annualmean of about 360 matmcm has a transitionaltype of annual course with
almost constant level of the total ozone
minimumduring the entire fall and ozonemaximumin MarchApril. Central Asia is the most southernregion, including stationsbetween38ø and 47øN. Its annualaverageis about330 matmcm and the annualcoursealthoughsimilar in the level of the annualminimum (-300 matmcm) like the Europeanpart is unique with its appearancekeeping low monthlyozonevalues dotted line. with only 1-2% fluctuationsfrom July to November.There is a differencein the level of the annual maximum (~370 matm cm) it is importantthat this correlationis followed in long-term which is ~ 10% lower thanin the Europeanpart and -20% lower variations andwhendiscrepanciei appear,theozonerecordfor than over Eastern Siberia- Far East. Figure 8 plots the annual the givenperiodis scrutinized.As an example,Figure6 shows coursesof four individual stationsrepresentingthe four regions long-termnormalized(fiYo)variationsof ozoneand temperature discussed in this study.From Figure 8 and Table 2 it is obvious for St. Petersburg and Petropavlovsk.Some quantitative that althoughthe ozoneincreasestartsin differentmonths(e.g., characteristics of this relation are shown in Figure 14 and Septemberin Western Siberia, November-Decemberin the discussed below.It shouldbe notedthat at moststations,during European part), the major month-to-monthincrement is the last few years, some discrepanciesappearedlarger than observedfrom Decemberto Januarywhen it is 8 to 11% of the beforeandtheywere'related to radiative effectsof volcanic respectiveregion'sannualmean.After the annualmaximumin aerosolin combinationwith the dynamicalof E1 Nifio-Southem the springthe ozonedeclinestartstowardApril in CentralAsia Oscillation(ENSO) effects[Randeland Cobb, 1994]. and EasternSiberia and it is strongernearly everywherein May It shouldbe notedthat somestations(e.g., Voronez,Pechora) to June, consistingof 8 to 13%. Over the Europeanpart the did not require any substantialcorrections.It means that following a proper method of observationsand control, the improvedM-83 and the M-124 filter instrumentscouldprovide
reliabledata.Theiraccuracy •s notsohighasfromtheDobson instrument, but it is about 3% for direct Sun measurementsand
5% for zenith sky observations.Within the individual station reevaluatedrecord,there are someperiodsfor whichdue to lack of comparisonand/orcalibrationcouldnot be reliably corrected nor so suspicious to be rejected.Fortunately,thesearevery few.
_
Since 1992, total ozone data, submitted to WO3DC in
Toronto,have to be basedon Bass-Paurabsorptioncoefficients, but for the homogeneityof this study,all of the data usedsince January1992 were recalculatedto the previousWMO-Vigroux
scale,effective before1992.Thefinallyreevaluated datasetof all stationsusedin this studyis being depositedto the WO3DC, Toronto, in the standard format to replace the previously publisheddata.
52 3. Basic Characteristics Distribution
90
of the Total Ozone
Althoughthe main characteristicof total ozoneclimatology couldbe derived now from the recentyearswith satellitedata [e.g., Herman et al., 1993; Herman and Larko, 1994], it is necessaryhere to highlight some not well-known specific featuresof total ozonedistributionover Europeand Asia north of 38øN based on a longer set of groundstation observations. Different parts of thesecontinentsexperienceslightlydifferent atmosphericcirculationregimes [e.g., Bojkov, 1968] and, as a
61 128
14290 19'80
!95
'179 19'90
Figure 5. Exampleof thecorrections of Dushanbedatabasedon the useof differentinstrumentsand their intercomparison. (Top) Original data versusTOMS overpasses smoothedby a 31-day running mean. (Bottom) Ozone data after correctionswere introducedwith an indicationof the numbersand the periodof use of various instruments.
BOJKOV
ET AL.'
TOTAL
OZONE
CHANGES
OVER
EURASIA
22,991
Here it is interesting to show how much the annual course has been distortedduring a recordlow ozonein the first half of 1993. Figure 9 plots the combinedaverageannual coursewith the +2o boundary(for the period 1973-1990) of Krasnoyarsk and Irkutsk as well as their monthly running mean of the 1993 values. Ozone deficiency of 50 to 90 matrecta from the long-termaverageduring the first 4 monthsof the year exceeds three standarddeviations.During the summerthe ozoneis in the lower boundary out of the 2o envelope and in the fall the -1 climatological"normal" values were reachedagain. This ozone anomalyis discussedfurtherin section4 below. As already mentioned, in March the highest total ozone 11 climatologicalvaluesin the entire GO3OS are observedover the Eastern Siberia- Far East region. Long-term monthly mean in March for Nagaevo and Nikolaevsk are 480-500 matmcm, whereas at the same latitudes over the European part of the former USSR they are only about 400 matracm. This ozone -1 maximum is well pronouncedin the top panel of Figure 10, --.................... ------------t,OZONE which showsthe map of the March monthlymean valuesbased oo on groundstationsfor the first 10 yearsof observations(1973-2 I I I 1982) of the period under consideration.Unlike satellite maps, with data availableonly since1979, theseground-basedmapsdo not include periods with substantialanomaliesin the ozone Figure 6. Twelve-monthrunningmeansof the normalized(A/o) layer. In summerthe EasternSiberia - Far East ozonemaximum monthlydeviationsof total ozonereviseddata (continuousline) disappearsand in August,shownin the bottompanel of Figure and 100 hPa temperature(dotted line) at (top) St. Petersburg 10, thereis no longitudinaldifferencein the ozonevalues.From and (bottom)Petropavlovskreveal very similar long-termcourse Septemberthe differencebetweenthe regionsstartsto build up of the variations of both parameters (especially over St. and the East Siberian maximum starts to appear again. The Petersburg).The arrows indicate times of the sharply defined naturalvariability of total ozoneis alsodifferentin the 2 months quasi-biennialeast wind maximumat 50-hPa in the equatorial represented on the maps. In winter-spring the standard zone used here as a proxy for the quasi-biennial oscillation deviationsof monthly mean values are about 20-26 matm cm, (QBO) scale. while in summerthey are only about 10-12 matm cm (see also Table 2).
I I
/ /.., i...' '.,.1 "
0
975
9'80
985
.990
99.5
The relative
annual decline is spread nearly equally between April and September. From Table 2 one could also estimate the average annual amplitude of the total ozone which is slightly above 100 matmcm (or -29% of the annualmean) for Central Europe,the Europeanpart of the former USSR, and Western Siberia. The amplitudeincreasesto above150 matmcm (-39% of the annual mean) for Eastern Siberia - Far East and is the same over the adjacentpolar region.As one could expectover Central Asia, the amplitudeis much smaller,-75 matmcm (only about22% of the annual mean). The monthswith annual minimum values are closeto 300 matm cm for Central Europe,the Europeanpart of the former USSR, and Central Asia; for Siberia they are just 3-4% higher. The regional differences are much more pronouncedin the annual maximums:in Eastern Siberia the maximumis by 17% strongerthanin similar latitudesin Europe servedby Dobsonand the Europeanpart of the formerUSSR, by 14% than in Western Siberia, and up to 26% higher than over Central
Asia.
It
should be noted
that the Siberian
excess of ozone over the Eastern Siberian
- Far
East region versus the more western part, including the European-Scandinavian region particularlyduring the cold part of the year shownalreadyin the analysisof polarozone[Bojkov, 1988] and recognizedby the TOMS measurements[Bowman and Kruger, 1985], is firmly establishedby the ground-based m atm
cm
5OO
. e- -e . 450
-
IE 400
-
350
-
•
,/• ,,
ST.PETERSBURG
--•'' IRKUTSK
B!,'
--•--
NAGAEVO
ozone
maximumis significantlystrongerthan the ozonemaximumof -440
matm cm observed
over
similar
latitudes
over Canada
[Bojkov,1988]. During the past 20 yearsin the springtime in the Siberian stationsthere are at least 30 days when the total ozone has exceeded 590 matm cm with a reliably measured absolutemaximum of slightly over 600 matmcm. Over the North American and European Dobson stations at similar latitudes,duringa longerobservational period(up to 35 years), there are only a half-dozenoccasionswith ozone above 590 matm
cm.
300
I
JAN
I
I
MAR
I
I
MAY
I
I
JUL
I
I
SEP
T
ß
NOV
Figure 7. Annual courseof the total ozonediffers substantially over the regions. While the European station (St. Petersburg) has a minimum in October-November, the Far East station
(Nagaevo) reaches its minimum as early as Augast. Siberia (Irkutsk)has a transitionaltype of annualcoursewith almosta constantlevel during the entire fall.
22,992
BOJKOV ET AL.: TOTAL
OZONE
CHANGES
OVER EURASIA
Table 2. Monthly Mean ValuesandStandardDeviations,Typicalfor Stationsin EachRegion for the Period 1973-1990 (matm cm) Region Central Asia
(42øN)
Jan.
Feb. March April May
Jun.
Jul.
Aug. Sept. Oct.
Nov.
Dec.
355
374
373
354
346
329
309
303
300
302
306
327
17
18
20
17
13
12
10
10
9
10
9
13
453
461
418
370
334
317
308
310 401
Polar region
(70øN)
33
20
15
15
11
15
15
19
441
468
472
455
416
373
337
319
326
346
368
20
21
24
20
16
13
13
12
13
13
17
20
Western Siberia
379
405
415
416
398
363
341
329
318
311
317
340
(56øN) Europeanpart (52øN)
19 354 21
28 385 27
27 400 25
23 402 20
16 383 15
14 366 12
10 347 11
11 331 11
10 315 11
12 302 12
13 302 12
18 327 17
Dobson'sEurope (51øN)
346 23
376 26
389 22
398 20
384 15
366 10
348 10
331 9
307 9
297 14
295 12
316 15
Eastern Siberia and
Far East(53øN)
The meanlatitudefor eachregionis given in parentheses.
data.In EasternSiberiatheozoneamountduringOctober-March Within each region there are latitudinal differencesin the exceedsthat over the European-Scandinavian sectorby more annualcourseof the individualstations.Thereforethe original than 20%, but duringthe summerit is nearlythe same.In time series of the stations were deseasonalized before use for the Eastern Siberia the annual increase starts2 months earlier and is
long-term variations and trend calculations.For this, for each
morevigorous.Someexplanationfor thesedifferencescouldbe
stationandfor eachmonthof theyear,the long-termmeanvalue was calculatedfor the period 1973-1990. Then this "norm"was subtractedfrom the time seriesof monthlytotal ozonevalues. The regional mean deviation values for each month were
deductedfrom the basic stratospheric circulationstudy of Pogosyan [1972]. He noted that meridional transformationsof
thelowerstratosphere circulation overSiberiaappearasearlyas October.During each short disturbancethe temperatureat calculatedby averagingstationdeviations.Althoughlong-term 100-hPaincreases by only30-5øbutnevertheless is accompanied meansof total ozoneare differentover differentregions,their by a slightozoneincrease,as demonstrated in the annualcourse. long-termvariationsshowa similardecline(seeFigure11). The reasonablesimilarity of the seasonalozone variationsdeduced from the Dobsonstationsin Europeand from the reevaluated filter data over the Europeanpart of the former USSR is easternend of the Asian continentbecomeswell established, apparentfrom the plotsin Figure 12.
During the following winter monthswith the increaseof the
temperature contrast between the Pacific and the eastern end of the Asian continent, the meridional circulation over the far
assisting theformationof a well-pronounced areawithrelatively
high stratospherictemperaturesand total ozone over Eastern Quasi-Biennial Oscillation (QBO) and El Nifio Southern Oscillation (ENSO) Siberia.
4. Long-Term Variations and Trends
Appearances of negativedeviationsin generalabout6 months after the easterlyequatorialstratosphericwind maximumsare
seenbothin Figures11 and12.Thesedeficiencies areespecially In the discussion of ozonevariationsand their possible well pronouncedafter the QBO in 1975, 1982, 1985, 1990, and
relationwith atmospheric circulation(e.g., QBO) as seenalsoin the stratospheric temperatures, it shouldbe kept in mind that
1992 althoughtheir amplitudemay differ from eventto event andoverthe regions.As it hasbeenshownearlier[e.g.Angell, after all corrections the data of some individual 1986,1990;Bojkov,1987,Zerefoset al., 1992]themagnitude of filter-ozonometer stationshave2-3% systematic errorsduring the ozonedeviations,which may be relatedto changesin the certainperiodsandeventhebeststations havefew, fortunately stratospherictransportinducedby the QBO [see Holton and rathershort,intervalswith missingdata.In thiscase,the levelof Tan, 1982], is influencedby a numberof factorsincludingthe error at individual stationsis higher and conclusions on trends canbe moreeasilydrawnby studyingthe averageseriesfor the regions.There are usuallysevento nine stationsin eachof the four regionsidentifiedin Figure 1 and errorsconnected with
QBO intensivityand the ozoneseasonat the time of QBO shift from easterlyto westerlywinds.It couldalsobe influencedby interactionwith the recurrenceat irregularintervalsof 3 to 6 yearsof anotheratmospheric phenomena knownto influencethe instrumentsare 2 to 3 times smaller for regionsthan for polewardtransportprocesses - the E1-NifioSouthernOscillation individual stations. Even if one or two station records are (ENSO) [e.g. Quiroz, 1983; Rasmusson,1985; Zerefos et missingat random,the combinedrecordis still sufficiently a/.,1992]. So far for the period under discussionhere, ENSO representative.A fifth region, of European stations with events have been well pronouncedin 1982, 1987, and 1992 Dobsons,was formedfrom the data of Arosa,Belsk, Bracknell, althoughtheyhavebeenregistered alsoin 1973and 1977. BuCharest, Budapest, Hohenpeissenberg, Hradec Kralove, Oslo, It is known that the ENSO cycle in the equatorialPacific andUcclestations for thecomparison withtheEuropean partof producesan atmosphericresponsethat extends from the the former USSR region. Some of these data were also troposphere up to about50-hPain the lower stratosphere. The reevaluatedrecently, their calibrationsand correctionswere global ozonedistributionis partly controlledby the Hadley taken into account. circulation and its upward extension affecting the lower
BOJKOV ET AL.' TOTAL OZONE CHANGES OVER EURASIA
is about4% also in other regions.It is importantto note that this objective analysis also confirms the appearanceof the ozone deficienciesin general about a half year after the equatorial stratosphericeasterly wind maximum. At the same time it shouldbe kept in mind that the filter is rather broad and may incorporatealsoa fractionof non-QBOs.
450
400
_ ,,
MOSCOW / -..X.,. xl"•" •
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350
Stratospheric Temperature and Ozone
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