K. Stebel

Norwegian Institute for Air Research, Kristiania (historical), Oslo, Norway

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Publications (98)156.94 Total impact

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    K. Stebel · A. Amigo · H. Thomas · A.J. Prata
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    ABSTRACT: Putana is a stratovolcano in the central Andes volcanic zone in northern Chile on the border with Bolivia. Fumarolic activiy has been visible at its summit crater at 5890 m altitude from long distances since the early 1800’s. However, due to its remote location neither detailed geological studies have been made nor gas fluxes have been monitored and therefore its evolution remains unknown. On November 28, 2012 an ultraviolet (UV) imaging camera was transported to Putana and for about 30 minutes images of the fumaroles were recorded at 12 Hz. These observations provide the first measurements of SO2 fluxes from the fumarolic field of Putana and demonstrate the applicability of the UV camera to detect such emissions. The measurement series was used to assess whether the sampling rate of the data influences the estimate of the gas flux. The results suggest that measurements made at 10 s and 1 minute intervals capture the inherent (turbulent) variability in both the plume/wind speed and SO2 flux. Relatively high SO2 fluxes varying between 0.3 kg s− 1 and 1.4 kg s− 1, which translates to 26 t/d and 121 t/d assuming constant degassing throughout the day, were observed on November 28, 2012. Furthermore, we demonstrates how an optical flow algorithm can be integrated with the SO2 retrieval to calculate SO2 fluxes at pixel level. Average values of 0.64 kg s− 1 ± 0.20 kg s− 1 and 0.70 kg s− 1 ± 0.53 kg s− 1 were retrieved from a "classical" transect method and the "advanced" optical flow based retrieval, respectively. Assuming constant emissions throughout all times, these values would results in an average annual SO2 burden of 20–22 kT.
    Full-text · Article · Jan 2015 · Journal of Volcanology and Geothermal Research
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    Full-text · Article · Jan 2015 · Earth-Science Reviews
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    ABSTRACT: Traditional validation of atmospheric profiles is based on the intercomparison of two or more data sets in predefined ranges or classes of a given observational characteristic such as latitude or solar zenith angle. In this study we trained a self-organising map (SOM) with a full time series of relative difference profiles of SCIAMACHY limb v5.02 and lidar ozone profiles from seven observation sites. Each individual observation characteristic was then mapped to the obtained SOM to investigate to which degree variation in this characteristic is explanatory for the variation seen in the SOM map. For the studied data sets, altitude-dependent relations for the global data set were found between the difference profiles and studied variables. From the lowest altitude studied (18 km) ascending, the most influencing factors were found to be longitude, followed by solar zenith angle and latitude, sensor age and again solar zenith angle together with the day of the year at the highest altitudes studied here (up to 45 km). After accounting for both latitude and longitude, residual partial correlations with a reduced magnitude are seen for various factors. However, (partial) correlations cannot point out which (combination) of the factors drives the observed differences between the ground-based and satellite ozone profiles as most of the factors are inter-related. Clustering into three classes showed that there are also some local dependencies, with for instance one cluster having a much stronger correlation with the sensor age (days since launch) between 36 and 42 km. The proposed SOM-based approach provides a powerful tool for the exploration of differences between data sets without being limited to a priori defined data subsets.
    Full-text · Article · Jan 2014
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    ABSTRACT: In this study we have analyzed whether tourist cruise ships have an influence on measured sulfur dioxide (SO2), ozone (O3), Aitken mode particle and equivalent black carbon (EBC) concentrations at Ny Ålesund and Zeppelin Mountain on Svalbard in the Norwegian Arctic, during summer. We separated the measurement data set into periods when ships were present and periods when no ships were present in the Kongsfjord area, according to a long-term record of the number of passengers visiting Ny Ålesund. We show that when ships with more than 50 passengers cruise in the Kongsfjord, measured daytime-mean concentrations of 60-nm particles and EBC in summer show enhancements of 72 and 45% relative to values when no ships are present. Even larger enhancements of 81 and 72% were found for stagnant conditions. In contrast, O3 concentrations were 5% lower on average and 7% lower under stagnant conditions, due to titration of O3 with the emitted nitric oxide (NO). The differences between the two data subsets are largest for the highest measured percentiles while relatively small differences were found for the median concentrations, indicating that ship plumes are sampled relatively infrequently even when ships are generally present but carry high concentrations. We estimate that the ships increased the total summer mean concentrations of SO2, 60-nm particles and EBC by 15, 18 and 11%, respectively. Our findings have two important implications: firstly, even at such a remote Arctic observatory as Zeppelin, the measurements can be influenced by tourist ship emissions. Careful data screening is recommended before summer-time Zeppelin data is used for data analysis or for comparison with global chemistry transport models. However, Zeppelin remains one of the most valuable Arctic observatories, as most other Arctic observatories face even larger local pollution problems. Secondly, given landing statistics of tourist ships on Svalbard, it is suspected that large parts of the Svalbard archipelago are affected by cruise ship emissions. Thus, our results may be taken as a warning signal of future pan-Arctic conditions, if Arctic shipping becomes more frequent and emission regulations are not strict enough.
    Full-text · Article · Aug 2013 · Atmospheric Chemistry and Physics
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    ABSTRACT: An unprecedented ozone loss occurred in the Arctic in spring 2011. The details of the event are re-visited from the twice-daily total ozone and NO2 columns measurements of the eight SAOZ/NDACC (Système d'Analyse par Observation Zénitale/Network for Detection of Atmospheric Composition Changes) stations in the Arctic. It is shown that the total ozone depletion in the polar vortex reached 38% (approx. 170 DU) by the end of March that is larger than the 30% of the previous record in 1996. Asides from the long extension of the cold stratospheric NAT PSC period, the amplitude of the event is shown to be resulting from a record daily total ozone loss rate of 0.7% day-1 after mid-February, never seen before in the Arctic but similar to that observed in the Antarctic over the last 20 yr. This high loss rate is attributed to the absence of NOx in the vortex until the final warming, in contrast to all previous winters where, as shown by the early increase of NO2 diurnal increase, partial renoxification is occurring by import of NOx or HNO3 from the outside after minor warming episodes, leading to partial chlorine deactivation. The cause of the absence of renoxification and thus of high loss rate, is attributed to a vortex strength similar to that of the Antarctic but never seen before in the Arctic. The total ozone reduction on 20 March was identical to that of the 2002 Antarctic winter, which ended around 20 September, and a 15-day extension of the cold period would have been enough to reach the mean yearly amplitude of the Antarctic ozone hole. However there is no sign of trend since 1994, neither in PSC volume, early winter denitrification, late vortex renoxification, and vortex strength nor in total ozone loss. The unprecedented large Arctic ozone loss in 2011 appears to resulting from an extreme meteorological event and there is no indication of possible strengthening related to climate change.
    Full-text · Dataset · Jul 2013
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    Full-text · Dataset · Jul 2013
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    Full-text · Dataset · Jul 2013
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    Full-text · Dataset · May 2013
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    ABSTRACT: An unprecedented ozone loss occurred in the Arctic in spring 2011. The details of the event are revisited from the twice-daily total ozone and NO2 column measurements of the eight SAOZ/NDACC (Système d'Analyse par Observation Zénithale/Network for Detection of Atmospheric Composition Changes) stations in the Arctic. It is shown that the total ozone depletion in the polar vortex reached 38% (approx. 170 DU) by the end of March, which is larger than the 30% of the previous record in 1996. Aside from the long extension of the cold stratospheric NAT PSC period, the amplitude of the event is shown to be resulting from a record daily total ozone loss rate of 0.7% d−1 after mid-February, never seen before in the Arctic but similar to that observed in the Antarctic over the last 20 yr. This high loss rate is attributed to the absence of NOx in the vortex until the final warming, in contrast to all previous winters where, as shown by the early increase of NO2 diurnal increase, partial renoxification occurs by import of NOx or HNO3 from the outside after minor warming episodes, leading to partial chlorine deactivation. The cause of the absence of renoxification and thus of high loss rate, is attributed to a vortex strength similar to that of the Antarctic but never seen before in the Arctic. The total ozone reduction on 20 March was identical to that of the 2002 Antarctic winter, which ended around 20 September, and a 15-day extension of the cold period would have been enough to reach the mean yearly amplitude of the Antarctic ozone hole. However there is no sign of trend since 1994, either in PSC (polar stratospheric cloud) volume (volume of air cold enough to allow formation of PSCs), early winter denitrification, late vortex renoxification, and vortex strength or in total ozone loss. The unprecedented large Arctic ozone loss in 2011 appears to result from an extreme meteorological event and there is no indication of possible strengthening related to climate change.
    Full-text · Article · May 2013 · Atmospheric Chemistry and Physics
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    ABSTRACT: The eruption of the Icelandic volcano Eyjafjallajökull in April-May 2010 represents a "natural experiment" to study the impact of volcanic emissions on a continental scale. For the first time, quantitative data about the presence, altitude, and layering of the volcanic cloud, in conjunction with optical information, are available for most parts of Europe derived from the observations by the European Aerosol Research Lidar NETwork (EARLINET). Based on multi-wavelength Raman lidar systems, EARLINET is the only instrument worldwide that is able to provide dense time series of high-quality optical data to be used for aerosol typing and for the retrieval of particle microphysical properties as a function of altitude. In this work we show the four-dimensional (4D) distribution of the Eyjafjallajökull volcanic cloud in the troposphere over Europe as observed by EARLINET during the entire volcanic event (15 April – 26 May 2010). All optical properties directly measured (backscatter, extinction, and particle linear depolarization ratio) are stored in the EARLINET database available at www.earlinet.org. A specific relational database providing the volcanic mask over Europe, realized ad hoc for this specific event, has been developed and is available on request at www.earlinet.org. During the first days after the eruption, volcanic particles were detected over Central Europe within a wide range of altitudes, from the upper troposphere down to the local Planetary Boundary Layer (PBL). After 19 April 2010, volcanic particles were detected over South and South Eastern Europe. During the first half of May (5–15 May), material emitted by the Eyjafjallajökull volcano was detected over Spain and Portugal and then over the Mediterranean and the Balkans. Last observations of the event were recorded until 25 May in Central Europe and in the Eastern Mediterranean area. The 4D distribution of volcanic aerosol layering and optical properties on European scale here reported provides an unprecedented data set for evaluating satellite data and aerosol dispersion models for this kind of volcanic events.
    Full-text · Article · Apr 2013 · Atmospheric Chemistry and Physics
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    [Show abstract] [Hide abstract]
    ABSTRACT: An unprecedented ozone loss occurred in the Arctic in spring 2011. The details of the event are re-visited from the twice-daily total ozone and NO2 columns measurements of the eight SAOZ/NDACC (Système d'Analyse par Observation Zénitale/Network for Detection of Atmospheric Composition Changes) stations in the Arctic. It is shown that the total ozone depletion in the polar vortex reached 38% (approx. 170 DU) by the end of March that is larger than the 30% of the previous record in 1996. Asides from the long extension of the cold stratospheric NAT PSC period, the amplitude of the event is shown to be resulting from a record daily total ozone loss rate of 0.7% day−1 after mid-February, never seen before in the Arctic but similar to that observed in the Antarctic over the last 20 yr. This high loss rate is attributed to the absence of NOx in the vortex until the final warming, in contrast to all previous winters where, as shown by the early increase of NO2 diurnal increase, partial renoxification is occurring by import of NOx or HNO3 from the outside after minor warming episodes, leading to partial chlorine deactivation. The cause of the absence of renoxification and thus of high loss rate, is attributed to a vortex strength similar to that of the Antarctic but never seen before in the Arctic. The total ozone reduction on 20 March was identical to that of the 2002 Antarctic winter, which ended around 20 September, and a 15-day extension of the cold period would have been enough to reach the mean yearly amplitude of the Antarctic ozone hole. However there is no sign of trend since 1994, neither in PSC volume, early winter denitrification, late vortex renoxification, and vortex strength nor in total ozone loss. The unprecedented large Arctic ozone loss in 2011 appears to resulting from an extreme meteorological event and there is no indication of possible strengthening related to climate change.
    Full-text · Article · Jan 2013 · Atmospheric Chemistry and Physics
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    Full-text · Article · Jan 2013 · Atmospheric Chemistry and Physics
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    [Show abstract] [Hide abstract]
    ABSTRACT: The eruption of the Icelandic volcano Eyjafjallajokull in April-May 2010 represents a "natural experiment" to study the impact of volcanic emissions on a continental scale. For the first time, quantitative data about the presence, altitude, and layering of the volcanic cloud, in conjunction with optical information, are available for most parts of Europe derived from the observations by the European Aerosol Research Lidar NETwork (EARLINET). Based on multi-wavelength Raman lidar systems, EARLINET is the only instrument worldwide that is able to provide dense time series of high-quality optical data to be used for aerosol typing and for the retrieval of particle microphysical properties as a function of altitude. In this work we show the four-dimensional (4-D) distribution of the Eyjafjallajokull volcanic cloud in the troposphere over Europe as observed by EARLINET during the entire volcanic event (15 April-26 May 2010). All optical properties directly measured (backscatter, extinction, and particle linear depolarization ratio) are stored in the EARLINET database available at www.earlinet.org. A specific relational database providing the volcanic mask over Europe, realized ad hoc for this specific event, has been developed and is available on request at www.earlinet.org. During the first days after the eruption, volcanic particles were detected over Central Europe within a wide range of altitudes, from the upper troposphere down to the local planetary boundary layer (PBL). After 19 April 2010, volcanic particles were detected over southern and south-eastern Europe. During the first half of May (5-15 May), material emitted by the Eyjafjallajokull volcano was detected over Spain and Portugal and then over the Mediterranean and the Balkans. The last observations of the event were recorded until 25 May in Central Europe and in the Eastern Mediterranean area. The 4-D distribution of volcanic aerosol layering and optical properties on European scale reported here provides an unprecedented data set for evaluating satellite data and aerosol dispersion models for this kind of volcanic events.
    Full-text · Article · Nov 2012 · Atmospheric Chemistry and Physics
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    ABSTRACT: Accuracy requirements for aerosol optical depth (AOD) in polar regions are much more stringent than those usually encountered in established sun photometer networks, while comparability of data from different archive centres is a further important issue. Therefore, two intercomparison campaigns were held during spring 2006 at Ny-Ålesund (Svalbard) and autumn 2008 at Izaña (Tenerife) within the framework of the IPY POLAR-AOD project, with the participation of various research institutions routinely employing different instrument models at Arctic and Antarctic stations. As reported here, a common algorithm was used for data analysis with the aim of minimizing a large part of the discrepancies affecting the previous studies. During the Ny-Ålesund campaign, spectral values of AOD derived from measurements taken with different instruments were found to agree, presenting at both 500 nm and 870 nm wavelengths average values of root mean square difference (RMSD) and standard deviation of the difference (SDD) equal to 0.003. Correspondingly, the mean bias difference (MBD) varied mainly between −0.003 and +0.003 at 500 nm, and between −0.004 and +0.003 at 870 nm. During the Izaña campaign, which was also intended as an intercalibration opportunity, RMSD and SDD values were estimated to be equal to 0.002 for both channels on average, with MBD ranging between −0.004 and +0.004 at 500 nm and between −0.002 and +0.003 at 870 nm. RMSD and SDD values for Ångström exponent α were estimated equal to 0.06 during the Ny-Ålesund campaign and 0.39 at Izaña. The results confirmed that sun photometry is a valid technique for aerosol monitoring in the pristine atmospheric turbidity conditions usually observed at high latitudes.
    Full-text · Article · Jun 2012 · Atmospheric Environment
  • K. Stebel · F. Prata · F. Dauge · A. Durant · A. Amigo
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    ABSTRACT: Only a few years ago spectral imaging cameras for SO2 plume monitoring were developed for remote sensing of volcanic plumes. We describe the development from a first camera using a single filter in the absorption band of SO2 to more advanced systems using several filters and an integrated spectrometer. The first system was based on the Hamamatsu C8484 UV camera (1344 x 1024 pixels) with high quantum efficiency in the UV region from 280 nm onward. At the heart of the second UV camera system, EnviCam, is a cooled Alta U47 camera, equipped with two on-band (310 and 315 nm) and two off-band (325 and 330 nm) filters. The third system utilizes again the uncooled Hamamatsu camera for faster sampling (~10 Hz) and a four-position filter-wheel equipped with two 10 nm filters centered at 310 and 330 nm, a UV broadband view and a blackened plate for dark-current measurement. Both cameras have been tested with lenses with different focal lengths. A co-aligned spectrometer provides a ~0.3nm resolution spectrum within the field-of-view of the camera. We describe the ground-based imaging cameras systems developed and utilized at our Institute. Custom made cylindrical quartz calibration cells with 50 mm diameter, to cover the entire field of view of the camera optics, are filled with various amounts of gaseous SO2 (typically between 100 and 1500 ppm•m). They are used for calibration and characterization of the cameras in the laboratory. We report about the procedures for monitoring and analyzing SO2 path-concentration and fluxes. This includes a comparison of the calibration in the atmosphere using the SO2 cells versus the SO2 retrieval from the integrated spectrometer. The first UV cameras have been used to monitor ship emissions (Ny-Ålesund, Svalbard and Genova, Italy). The second generation of cameras were first tested for industrial stack monitoring during a field campaign close to the Rovinari (Romania) power plant in September 2010, revealing very high SO2 emissions (> 1000 ppm•m). The second generation cameras are now used by students from several universities in Romania. The newest system has been tested for volcanic plume monitoring at Turrialba, Costa Rica in January, 2011, at Merapi volcani, Indonesia in February 2011, at Lascar volcano in Chile in July 2011 and at Etna/Stromboli (Italy) in November 2011. Retrievals from some of these campaigns will be presented.
    No preview · Article · Apr 2012
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    ABSTRACT: The amount of ozone depletion in the Arctic is monitored every year since 1994 by comparison between total ozone measurements of the SAOZ / NDACC UV-Vis spectrometer and 3-D chemical transport model simulations in which ozone is considered as a passive tracer. The method allows to determine the period and the daily rate of ozone destruction and to calculate the amplitude of the cumulative loss at the end of the winter. The destruction is found to be highly dependent on the stratospheric temperature history, varying between 0-10% in relatively warm and short vortex duration years to 25-30% in colder and longer ones with an exception during the winter 2010/2011 when an unprecedented depletion of 39% was reported. In this study, preliminary results for the winter 2011/12 will be presented and compared to previous winters. The focus will be put on the timing of the chemical ozone loss and on the ability of two 3D CTM (Reprobus and Slimcat) to reproduce the loss.
    Full-text · Article · Apr 2012
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    ABSTRACT: The Eyjafjallajokull ash that crossed over Spain and Portugal on 6-12 May 2010 has been monitored by a set of operational sun photometer sites within AERONET-RIMA and satellite sensors. The sun photometer observations (aerosol optical depth, coarse mode concentrations) and ash products from IASI and SEVIRI satellite sensors, together with FLEXPART simulations of particle transport, allow identifying the volcanic aerosols. The aerosol columnar properties derived from inversions were investigated, indicating specific properties, especially regarding the absorption. The single scattering albedo was high (0.95 at 440 nm) and nearly wavelength independent, although with slight decrease with wavelength. Other parameters, like the fine mode fraction of the volume size distributions (0.20-0.80) or the portion of spherical particles (15-90%), were very variable among the sites and indicated that the various ash clouds were inhomogeneous with respect to particle size and shape.
    Full-text · Article · Mar 2012 · Atmospheric Environment
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    ABSTRACT: Accuracy requirements for aerosol optical depth (AOD) in polar regions are much more stringent than those usually encountered in established sun photometer networks, while comparability of data from different archive centres is a further important issue. Therefore, two intercomparison campaigns were held during spring 2006 at Ny-Ålesund (Svalbard) and autumn 2008 at Izaña (Tenerife) within the framework of the IPY POLAR-AOD project, with the participation of various research institutions routinely employing different instrument models at Arctic and Antarctic stations. As reported here, a common algorithm was used for data analysis with the aim of minimizing a large part of the discrepancies affecting the previous studies. During the Ny-Ålesund campaign, spectral values of AOD derived from measurements taken with different instruments were found to agree, presenting at both 500 nm and 870 nm wavelengths average values of root mean square difference (RMSD) and standard deviation of the difference (SDD) equal to 0.003. Correspondingly, the mean bias difference (MBD) varied mainly between À0.003 and þ0.003 at 500 nm, and between À0.004 and þ0.003 at 870 nm. During the Izaña campaign, which was also intended as an intercalibration opportunity, RMSD and SDD values were estimated to be equal to 0.002 for both channels on average, with MBD ranging between À0.004 and þ0.004 at 500 nm and between À0.002 and þ0.003 at 870 nm. RMSD and SDD values for Ångström exponent a were estimated equal to 0.06 during the Ny-Ålesund campaign and 0.39 at Izaña. The results confirmed that sun photometry is a valid technique for aerosol monitoring in the pristine atmospheric turbidity conditions usually observed at high latitudes.
    Full-text · Article · Jan 2012 · Atmospheric Environment
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    ABSTRACT: Since 2002 sun photometer measurements were carried out at Andenes (Norway), in the ALOMAR observatory, to investigate the aerosol optical properties in the European sub-Arctic region. From 2002 to 2005 measurements were performed during summer campaigns. Since 2006 a Cimel sun photometer has been permanently deployed at the site. The instrument is part of the Red Ibérica de medida de Aerosoles Atmosféricos aerosol robotic network (RIMA–AERONET). The aerosol optical depth (AOD) and the Ångström exponent (AE) were analysed to investigate the aerosol content, type and seasonality in this sub-Arctic location. Back trajectories were used to provide information about the air-mass origin, especially for cases of moderate turbidity produced by long-range transported aerosols from mid-latitudes. The AOD was in general very low, with mean AOD units of 0.10 ± 0.05 and characteristics of clean continental or marine type aerosols (AE = 1.2 ± 0.4). The lower mean monthly values were obtained in February (0.04) and November (0.06), and the maximum was found in May (0.12). Episodes of long-range transported aerosol occurred at any time when observations were made, with the highest frequency in May, and originated in central and eastern Europe. The associated air masses transported anthropogenic pollution, biomass burning aerosols and in some cases also Saharan dust. A characterization of microphysical properties was performed, showing that the fine mode dominated the particle size distribution, with an average fine mode volume fraction of 0.69. In Arctic regions, enhanced levels of aerosol concentrations occur frequently in late winter and spring due Arctic haze. In our study such hazy periods were not observed at Andenes. Copyright © 2011 Royal Meteorological Society
    No preview · Article · Jan 2012 · Quarterly Journal of the Royal Meteorological Society
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    ABSTRACT: The amount of ozone depletion in the Arctic has been monitored every year since 1994 by comparison between total ozone measurements of the SAOZ / NDACC UV-Vis spectrometer stations and 3-D chemical transport model simulations in which ozone is considered as a passive tracer. The destruction is found to be highly dependent on the stratospheric temperature history of the winter, varying between 0-10% in relatively warm and short vortex duration years to 25-30% in colder and longer ones. Compared to these 17 previous years, the winter 2010/2011 displays an unprecedented depletion of 39% in the polar vortex. The destruction started in early January and remained limited to 10% until mid-February. However, the depletion accelerated afterwards and a daily loss rate of about 0.8 DU/day was estimated until late March. Analysis with ozonesonde measurements from Sodankyla launched on March 30, also showed a reduction of about 80% of ozone between 18 and 21 km consistent with the total column loss estimations. This unusual depletion is attributed to an extremely cold stratosphere during the late winter, colder than any year since 1994 in March, due to the limited amplitude of planetary waves in 2010/2011. It is shown to even exceed that of 1997 when the vortex remained until early April. Although extreme and reaching in March a rate similar to that of September over Antarctica, the depletion is still smaller than that derived by the same method in Antarctica for 23 years, where, with the exception of 2002, it systematically reaches 50-52%. The event offers a challenging opportunity for testing the ability of 3-D chemical transport models to capture the depletion under these extreme Arctic conditions. In this study, the loss is shown to be underestimated by REPROBUS and overestimated by SLIMCAT. Possible reasons for this will be discussed.
    No preview · Article · Dec 2011

Publication Stats

1k Citations
156.94 Total Impact Points

Institutions

  • 2003-2015
    • Norwegian Institute for Air Research
      Kristiania (historical), Oslo, Norway
  • 2004-2005
    • Norsk Treteknisk Institutt
      Kristiania (historical), Oslo, Norway
  • 1998-2004
    • Swedish Institute of Space Physics
      Kiruna, Norrbotten, Sweden
  • 1997
    • Institutet för rymdfysik
      Kiruna, Norrbotten, Sweden