Figure 1. Time series of the monthly mean temperatures (°C) at 30 hPa over the North Pole inMarch, 1956 to 2004. Linear trends are given for three different periods: 1956-1979, 1979-2004and 1956-2004 (Labitzke and van Loon, 1999, updated). Data: Free University Berlin (FUB)(open dots), ECMXF (full dots).

The Lower Arctic Stratosphere in Winter since 1952: an Update

KKaarriinn LLaabbiittzzkkee, Freie Universität Berlin, Germany (labitzke@strat01.met.fu-berlin.de)BBaarrbbaarraa NNaauujjookkaat, Freie Universität Berlin, GermanyMMaarrkkuuss KKuunnzzee, Freie Universität Berlin, Germany

Four years ago we published a tablewith monthly mean temperatures

(ºC) at 30 hPa over the North Pole([Labitzke and Naujokat, 2000], hereafterLN). These data started with the winter1955/56, i.e. 45 winters were available.One point of interest in the paper wasthe fact that there was a period of 7 win-ters without Major Warmings: NorthernHemisphere winter 1991/92 to 1997/1998. We pointed out that during lowsolar activity the winters in the westphase of the Quasi-Biennial Oscillation(QBO) tended to be cold and stable(Labitzke and van Loon, 2000) and thiscombination existed during 4 out of the7 winters.

Here, we would like to give a follow upon the North Pole temperatures and onthe characteristics of the last four Arcticwinters by supplementing Table 1 of LN.After the extremely cold winter of1999/2000 (LN), we observed four high-ly disturbed winters with a total of fiveMajor Warmings (Table 1). Two of therecent winters belong to the winters inthe west phase of the QBO and high solaractivity, and they are expected to be con-nected with Major Warmings.

Particularly interesting was the winter of2001/2002 when two Major Warmingsoccurred in December and in February(Naujokat et al., 2000). This has beenobserved only once before, during thewinter of 1998/99.

Compared with our earlier results (Table 1 in LN) the overall trend has notchanged much during early and mid-winter. The trend over the Arctic lowerstratosphere is clearly negative inNovember and practically zero fromDecember till February.

Major Midwinter Warmings are connect-ed with the breakdown of the polar vor-tex, much reduced activity of planetarywaves, and weak transport of energy.This leads often in late winter to the re-establishment of a persistent cold polarvortex and to the so-called late wintercooling, which is clearly visible in theArctic temperatures during March andApril, especially in the 2003/04 winter

Table 1. RJ is the monthly mean of the sunspot numbers in January; in the column marked QBOthe phase of the QBO is given (determined using the equatorial winds between 50 and 40 hPa inJanuary-February); FW gives an indication of the timing of the Final Warmings which are thetransitions from the winter to the summer circulation. CW stands for Canadian Warmings and *indicates the occurrence of a Major Mid-Winter Warming. The long-term mean and the standarddeviation are based on the period 1955/56 to 2003/04. The values of the linear trend are for the fulldata set, n=49 years. C stands for a cold monthly mean (about half a standard deviation or morebelow the long term average; see discussion in LN). [Data: Free University Berlin (FUB) until2000/01, ECMWF afterwards]

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Labitzke, K. and B. Naujokat, The lower arcticstratosphere in winter since 1952. SPARCNewsletter, 15, 11-14, 2000.

Labitzke, K. and M. Kunze, Stratospheric tem-peratures over the Arctic: Comparison ofthree data sets. Submitted to Meteorolog.Zeitschrift, 2004.

Naujokat, B., et al., 2002: The early majorwarming in December 2001—exceptional?.Geophys. Res. Lett., 29 (21), 2023,doi:10.1029/2002GL015316, 2

The Earth’s Protective Ozone Layer still Remains Vulnerable

Report on the Quadrennial Symposium on Atmospheric Ozone, Kos, Greece, 1-8 June 2004

CChhrriissttooss SS.. ZZeerreeffoos, University of Athens, Greece (zerefos@geol.uoa.gr)

The XX Quadrennial Symposium onAtmospheric Ozone coincided with the20th anniversary of the discovery of thespringtime Antarctic ozone hole. It alsomarked two decades of intensified glob-al atmospheric monitoring, and basicresearch in atmospheric chemistry andphysics. The progress in our understand-ing of the impact of human activities onthe chemistry and physics of the globalstratosphere since the previous Qua-drennial Ozone Symposium was pre-sented among the 690 research papers atthe XX Quadrennial Ozone Symposium,which was attended by 450 scientistsfrom 60 countries. For the papers pre-sented and the proceedings of theSymposium see http://www.QOS2004.gr.

Among the important topics discussed atthe Symposium were recent research onpossible ozone recovery, results from anexpanded network of satellites andground-based stations, ozone-climateinteractions, modelling and chemistry,results from monitoring of the globalcomposition of the troposphere fromsatellites, and measurements of UV-Bsolar radiation reaching ground level,among others.

Evidence was presented that ozone inthe past few years has been a little high-er than expected from earlier projectionsbased on sensitivity of ozone to influ-ences of aerosols, halogen compoundsand the solar cycle. The data may indi-

cate the beginning of a recovery; an issuethat is complicated by a number of fac-tors among which is the prominent roleplayed by changes in meteorology,greenhouse gases and in the radiationbalance, not excluding the observedrecovery of the ozone layer from its per-turbation by the volcanic eruption ofPinatubo in the early 90s. The evaluationof future ozone recovery in a changingclimate and the effect of ozone on thatclimate has shown the importance offeedback mechanisms between watervapour content and a warmer planet.

The need for the continuation of well-cal-ibrated instruments and measurementswas discussed extensively, and emphasiswas given to the use of satellite andground-based data (e.g. NDSC and theGlobal Ozone Observing System) to eval-uate models and ozone loss, and itsexpected recovery.

Numerous chemistry/climate modelswere presented at the conference. Theyaddressed the problem of how changesin meteorology or climate interact withchanges in the chemistry of ozone. Oneproblem is how changes in meteorologyover the last 25 years may have con-tributed to observed ozone changes andfeedback mechanisms. Models can thenbe used to extrapolate that knowledge towhat may happen in the future with theexpected increase in methane, nitrousoxide, and carbon dioxide.

Significant new work that combinessatellite and in situ observations withmodel calculations was presented at theSymposium, providing an insight intothe budget of nitrogen oxides and arange of halogen species, which areindispensable to our understanding ofthe global carbon and hydrologicalcycles. Water vapour presents a particu-larly important challenge. Satellite datashown at the meeting is not consistentwith trends from previous ground-baseddata. Understanding the feedback mech-anism between water vapour content,ozone, and polar stratospheric clouds iscritical to the evaluation of predictions ofozone in a future warmer global atmo-sphere.

Important progress was made in moni-toring the tropospheric ozone budgetwith the development of new observa-tional techniques from satellites, com-bined with models of tropospheric com-position. It turns out that the key factorsinfluencing the tropospheric ozonebudget (precursors, long-range transportin the troposphere and intrusions fromthe stratosphere) make the determina-tion and attribution of troposphericozone trends difficult.

Long-range transport of troposphericpollution and its coupling to climate wastargeted in a number of studies using cli-mate/chemistry models. Other studieshave shown the importance of long-

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(Table 1). In all four winters the FinalWarmings were late.

Figure 1 shows the time series of the 30 hPa North Pole temperatures (ºC) forMarch, an update of Figure 1 in LN. Theoverall trend for 49 years is weakly neg-ative, but depending on how one dividesthe data, the trend can be positive, as inthe first half of the data set or negative, asin the second half of the data. The changein the sign of the trend between the twodifferent periods is, however, confirmedby the re-analyses of NCEP/NCAR andby the ECMWF-ERA-40 data (Labitzkeand Kunze, submitted).

Acknowledgements

FU-Berlin: http://strat-www.met.fu-berlin.de/products/cdromNCEP/NCAR: http://wesley.wwb.noaa.gov/reanalysis.htmlERA40: http://www.ecmwf.int/research/era

RReeffeerreenncceess

Labitzke, K. and H. van Loon, The Strato-sphere: Phenomena, History, and Relevance.New York: Springer, Berlin Heidelberg, 1999.

Labitzke, K. and H. van Loon, The QBO effecton the global stratosphere in northern winter.J. Atmos. Sol. Terrest. Phys., 62, 621-628, 2000. •