scholarly journals Dynamics and chemistry of vortex remnants in late Arctic spring 1997 and 2000: Simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

2003 ◽  
Vol 3 (1) ◽  
pp. 1051-1080 ◽  
Author(s):  
P. Konopka ◽  
J.-U. Grooß ◽  
S. Bausch ◽  
R. Müller ◽  
D. S. McKenna ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Effective Diffusivity ◽  
Lagrangian Model ◽  
The Arctic ◽  
Summer Circulation ◽  
Air Masses ◽  
Ozone Loss ◽  
Mixing Ratios ◽  
Photochemical Decomposition ◽  
The Impact

Abstract. High resolution simulations of the chemical composition of the Arctic stratosphere during late spring 1997 and 2000 have been conducted with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations were performed for the entire northern hemisphere on two isentropic levels 450 K (~18 km) and 585 K (~24 km). The spatial distribution and the lifetime of the vortex remnants formed after the vortex breakup in May 1997 show a completely different behavior above and below 20 km. Above 20 km, vortex remnants effectively propagate southward (up to 40° N) and are "frozen'' in the summer circulation without significant mixing. Below 20 km the southward propagation of the remnants is bounded by the subtropical jet near 55° N. Their lifetime is shorter by a factor of 2 than above 20 km, owing to significant stirring below this altitude. The behavior of vortex remnants formed in March 2000 is similar but, due to an earlier vortex breakup, dominated until mid of May by westerly winds, even above 20 km. Vortex remnants formed in May 1997 are characterized by large mixing ratios of HCl indicating a negligible contribution of the halogen-induced ozone loss. In contrast, mid-latitude ozone loss in late boreal spring 2000 is dominated by an irreversible transport of the ozone-depleted polar air masses (dilution) and, until mid of April, by halogen-induced ozone destruction within the vortex remnants. By varying the effective diffusivity of CLaMS, the impact of mixing on the formation of ClONO2 and ozone depletion is considered. In particular, the photochemical decomposition of HNO3 and not mixing with NOx-rich mid-latitude air is the main source of NOx within the vortex remnants in March and April 2000. Ozone depletion in the remnants is driven by ClOx photolytically formed from ClONO2 and can be properly resolved for CLaMS spatial resolution better then 100\\,km. At 450 K, ozone loss in the vortex remnants contributes by ~2% to the ozone deficit poleward of 30° N.

scholarly journals Dynamics and chemistry of vortex remnants in late Arctic spring 1997 and 2000: Simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

2003 ◽  
Vol 3 (3) ◽  
pp. 839-849 ◽  
Author(s):  
P. Konopka ◽  
J.-U. Grooß ◽  
S. Bausch ◽  
R. Müller ◽  
D. S. McKenna ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Polar Vortex ◽  
Lagrangian Model ◽  
The Arctic ◽  
Summer Circulation ◽  
Air Masses ◽  
Ozone Loss ◽  
Mixing Ratios ◽  
Photochemical Decomposition ◽  
The Impact

Abstract. High-resolution simulations of the chemical composition of the Arctic stratosphere during late spring 1997 and 2000 were performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations were performed for the entire northern hemisphere on two isentropic levels 450 K (~18 km) and 585 K (~24 km). The spatial distribution and the lifetime of the vortex remnants formed after the vortex breakup in May 1997 display different behavior above and below 20 km. Above 20 km, vortex remnants propagate southward (up to 40°N) and are "frozen in'' in the summer circulation without significant mixing. Below 20 km the southward propagation of the remnants is bounded by the subtropical jet. Their lifetime is shorter by a factor of 2 than that above 20 km, owing to significant stirring below this altitude. The behavior of vortex remnants formed in March 2000 is similar but, due to an earlier vortex breakup, dominated during the first 6 weeks after the vortex breakup by westerly winds, even above 20 km. Vortex remnants formed in May 1997 are characterized by large mixing ratios of HCl indicating negligible, halogen-induced ozone loss. In contrast, mid-latitude ozone loss in late boreal spring 2000 is dominated, until mid-April, by halogen-induced ozone destruction within the vortex remnants, and subsequent transport of the ozone-depleted polar air masses (dilution) into the mid-latitudes. By varying the intensity of mixing in CLaMS, the impact of mixing on the formation of ClONO2 and ozone depletion is investigated. We find that the photochemical decomposition of HNO3 and not mixing with NOx-rich mid-latitude air is the main source of NOx within the vortex remnants in March and April 2000. Ozone depletion in the remnants is driven by ClOx photolytically formed from ClONO2. At the end of May 1997, the halogen-induced ozone deficit at 450 K poleward of 30°N amounts to ~12% with ~10% in the polar vortex and ~2% in well-isolated vortex remnants after the vortex breakup.

scholarly journals The impact of mid-latitude intrusions into the polar vortex on ozone loss estimates

2002 ◽  
Vol 2 (6) ◽  
pp. 2489-2506
Author(s):  
J.-U. Grooß ◽  
R. Müller
Keyword(s):  
Loss Rate ◽  
Polar Vortex ◽  
Lagrangian Model ◽  
The Arctic ◽  
Mixing Ratio ◽  
Match Method ◽  
Air Masses ◽  
Model Simulations ◽  
Ozone Loss ◽  
The Impact

Abstract. Current stratospheric chemical model simulations underestimate substantially the large ozone loss rates that are derived for the Arctic from ozone sondes for January of some years. Until now, no explanation for this discrepancy has been found. Here, we examine the influence of intrusions of mid-latitude air into the polar vortex on these ozone loss estimates. This study focuses on the winter 1991/92. It is based on simulations performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations for January 1992 show that the intrusions induce a reduction of vortex average ozone mixing ratio corresponding to a systematic offset of the ozone loss rate of about 12 ppb per day. Further, the results of the Match method are influenced by the intrusions, since the intruded air masses are deformed and reach dimensions below the Match radius. From our calculations we deduce a systematic offset of the Match ozone loss rate by about 10 ppb/day, which may explain about 28% of the published discrepancy between Match and box model simulations for the winter 1991/92.

scholarly journals Nitrification of the lowermost stratosphere during the exceptionally cold Arctic winter 2015–2016

2019 ◽  
Vol 19 (21) ◽  
pp. 13681-13699 ◽  
Author(s):  
Marleen Braun ◽  
Jens-Uwe Grooß ◽  
Wolfgang Woiwode ◽  
Sören Johansson ◽  
Michael Höpfner ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Cross Sections ◽  
Large Scale ◽  
Potential Temperature ◽  
Lagrangian Model ◽  
The Arctic ◽  
Small Scale ◽  
Mixing Ratios ◽  
Fine Structures ◽  
The Impact

Abstract. The Arctic winter 2015–2016 was characterized by exceptionally low stratospheric temperatures, favouring the formation of polar stratospheric clouds (PSCs) from mid-December until the end of February down to low stratospheric altitudes. Observations by GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) on HALO (High Altitude and LOng range research aircraft) during the PGS (POLSTRACC–GW-LCYCLE II–SALSA) campaign from December 2015 to March 2016 allow the investigation of the influence of denitrification on the lowermost stratosphere (LMS) with a high spatial resolution. Two-dimensional vertical cross sections of nitric acid (HNO3) along the flight track and tracer–tracer correlations derived from the GLORIA observations document detailed pictures of wide-spread nitrification of the Arctic LMS during the course of an entire winter. GLORIA observations show large-scale structures and local fine structures with enhanced absolute HNO3 volume mixing ratios reaching up to 11 ppbv at altitudes of 13 km in January and nitrified filaments persisting until the middle of March. Narrow coherent structures tilted with altitude of enhanced HNO3, observed in mid-January, are interpreted as regions recently nitrified by sublimating HNO3-containing particles. Overall, extensive nitrification of the LMS between 5.0 and 7.0 ppbv at potential temperature levels between 350 and 380 K is estimated. The GLORIA observations are compared with CLaMS (Chemical Lagrangian Model of the Stratosphere) simulations. The fundamental structures observed by GLORIA are well reproduced, but differences in the fine structures are diagnosed. Further, CLaMS predominantly underestimates the spatial extent of HNO3 maxima derived from the GLORIA observations as well as the overall nitrification of the LMS. Sensitivity simulations with CLaMS including (i) enhanced sedimentation rates in case of ice supersaturation (to resemble ice nucleation on nitric acid trihydrate (NAT)), (ii) a global temperature offset, (iii) modified growth rates (to resemble aspherical particles with larger surfaces) and (iv) temperature fluctuations (to resemble the impact of small-scale mountain waves) slightly improved the agreement with the GLORIA observations of individual flights. However, no parameter could be isolated which resulted in a general improvement for all flights. Still, the sensitivity simulations suggest that details of particle microphysics play a significant role for simulated LMS nitrification in January, while air subsidence, transport and mixing become increasingly important for the simulated HNO3 distributions towards the end of the winter.

scholarly journals Nitrification of the lowermost stratosphere during the exceptionally cold Arctic winter 2015/16

2019 ◽  
Author(s):  
Marleen Braun ◽  
Jens-Uwe Grooß ◽  
Wolfgang Woiwode ◽  
Sören Johansson ◽  
Michael Höpfner ◽  
...  
Keyword(s):  
Cross Sections ◽  
Large Scale ◽  
Potential Temperature ◽  
Lagrangian Model ◽  
The Arctic ◽  
Small Scale ◽  
Mountain Waves ◽  
Mixing Ratios ◽  
Fine Structures ◽  
The Impact

Abstract. The Arctic winter 2015/16 was characterized by exceptionally cold stratospheric temperatures, favouring the formation of polar stratospheric clouds (PSCs) from mid-December until the end of February down to low stratospheric altitudes. Observations by GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) on HALO (High Altitude and LOng range research aircraft) during the PGS (POLSTRACC/GW-LCYLCE II/SALSA) campaign from December 2015 to March 2016 allow an investigation of the influence of denitrification on the lowermost stratosphere (LMS) with a high spatial resolution. For the first time vertical cross-sections of nitric acid (HNO3) along the flight track and tracer-tracer correlations derived from the GLORIA observations document detailed pictures of wide-spread nitrification of the Arctic LMS during the course of an entire winter. GLORIA observations show large-scale structures and local fine structures with strongly enhanced absolute HNO3 volume mixing ratios reaching up to 11 ppbv at altitudes of 11 km in January and nitrified filaments persisting until the middle of March. Narrow streaks of enhanced HNO3, observed in mid-January, are interpreted as regions recently nitrified by sublimating HNO3-containing particles. Overall, a nitrification of the LMS between 5.0 ppbv and 7.0 ppbv at potential temperature levels between 350 and 380 K is estimated. This extent of nitrification has never been observed before in the Arctic lowermost stratosphere. The GLORIA observations are compared with CLaMS (Chemical Lagrangian Model of the Stratosphere) simulations. The fundamental structures observed by GLORIA are well reproduced, but differences in the fine structures are diagnosed. Further, CLaMS predominantly underestimates the spatial extent of maximum HNO3 mixing ratios derived from the GLORIA observations as well as the enhancement at lower altitudes. Sensitivity simulations with CLaMS including (i) enhanced sedimentation rates in case of ice supersaturation (to resemble ice nucleation on NAT), (ii) a global temperature offset, (iii) modified growth rates (to resemble aspherical particles with larger surfaces) and (iv) temperature fluctuations (to resemble the impact of small-scale mountain waves) mostly improve the agreement with the GLORIA observations. The sensitivity simulations suggest that details of particle microphysics play a significant role for simulated LMS nitrification in January, while air subsidence, transport and mixing become increasingly important towards the end of the winter.

scholarly journals The impact of mid-latitude intrusions into the polar vortex on ozone loss estimates

2003 ◽  
Vol 3 (2) ◽  
pp. 395-402 ◽  
Author(s):  
J.-U. Grooß ◽  
R. Müller
Keyword(s):  
Large Scale ◽  
Loss Rate ◽  
Polar Vortex ◽  
Control Measures ◽  
Lagrangian Model ◽  
The Arctic ◽  
Match Method ◽  
Ozone Loss ◽  
The Impact ◽  
Loss Rates

Abstract. Current stratospheric chemical model simulations underestimate substantially the large ozone loss rates that are derived for the Arctic from ozone sondes for January of some years. Until now, no explanation for this discrepancy has been found. Here, we examine the influence of intrusions of mid-latitude air into the polar vortex on these ozone loss estimates. This study focuses on the winter 1991/92, because during this winter the discrepancy between simulated and experimentally derived ozone loss rates is reported to be the largest. Also during the considered period the vortex was disturbed by a strong warming event with large-scale intrusions of mid-latitude air into the polar vortex, which is quite unusual for this time of the year. The study is based on simulations performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). Two methods for determination the ozone loss are investigated, the so-called vortex average approach and the Match method. The simulations for January 1992 show that the intrusions induce a reduction of vortex average ozone mixing ratio corresponding to a systematic offset of the ozone loss rate of about 12 ppb per day. This should be corrected for in the vortex average method. The simulations further suggest, that these intrusions do not cause a significant bias for the Match method due to effective quality control measures in the Match technique.

scholarly journals Modelling the effect of denitrification on polar ozone depletion for Arctic winter/spring 2004/05

2011 ◽  
Vol 11 (2) ◽  
pp. 3857-3884 ◽  
Author(s):  
W. Feng ◽  
M. P. Chipperfield ◽  
S. Davies ◽  
G. W. Mann ◽  
K. S. Carslaw ◽  
...  
Keyword(s):  
Standard Model ◽  
Ozone Depletion ◽  
Transport Model ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Particle Sedimentation ◽  
Ozone Loss ◽  
The Standard Model ◽  
The Impact ◽  
Polar Ozone

Abstract. A three-dimensional (3-D) chemical transport model (CTM), SLIMCAT, has been used to quantify the effect of denitrification on ozone loss for the Arctic winter/spring 2004/05. The simulated HNO3 is found to be highly sensitive to the polar stratospheric cloud (PSC) scheme used in the model. Here the standard SLIMCAT full chemistry model, which uses a thermodynamic equilibrium PSC scheme, overpredicts the Arctic ozone loss for Arctic winter/spring 2004/05 due to the overestimation of denitrification and stronger chlorine activation than observed. A model run with a detailed microphysical denitrification scheme, DLAPSE (Denitrification by Lagrangian Particle Sedimentation), is less denitrified than the standard model run and better reproduces the observed HNO3 as measured by Airborne SUbmillimeter Radiometer (ASUR) and Aura Microwave Limb Sounder (MLS) instruments. The overestimated denitrification causes a small overestimation of Arctic polar ozone loss (~5–10% at ~17 km) by the standard model. Use of the DLAPSE scheme improves the simulation of Arctic ozone depletion compared with the inferred partial column ozone loss from ozonesondes and satellite data. Overall, denitrification is responsible for a ~30% enhancement in O3 depletion for Arctic winter/spring 2004/05, suggesting that the successful simulation of the impact of denitrification on Arctic ozone depletion also requires the use of a detailed microphysical PSC scheme in the model.

scholarly journals Reactive nitrogen, ozone and ozone production in the Arctic troposphere and the impact of stratosphere-troposphere exchange

2011 ◽  
Vol 11 (24) ◽  
pp. 13181-13199 ◽  
Author(s):  
Q. Liang ◽  
J. M. Rodriguez ◽  
A. R. Douglass ◽  
J. H. Crawford ◽  
J. R. Olson ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Stratospheric Ozone ◽  
Arctic Region ◽  
Ozone Production ◽  
The Arctic ◽  
Subsequent Formation ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The Impact

Abstract. We use aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission to examine the distributions and source attributions of O3 and NOy in the Arctic and sub-Arctic region. Using a number of marker tracers, we distinguish various air masses from the background troposphere and examine their contributions to NOx, O3, and O3 production in the Arctic troposphere. The background Arctic troposphere has a mean O3 of ~60 ppbv and NOx of ~25 pptv throughout spring and summer with CO decreasing from ~145 ppbv in spring to ~100 ppbv in summer. These observed mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in emissions and stratospheric ozone layer in the past two decades that influence Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses, with mean O3 concentrations of 140–160 ppbv, are significant direct sources of O3 in the Arctic troposphere. In addition, air of stratospheric origin displays net O3 formation in the Arctic due to its sustainable, high NOx (75 pptv in spring and 110 pptv in summer) and NOy (~800 pptv in spring and ~1100 pptv in summer). The air masses influenced by the stratosphere sampled during ARCTAS-B also show conversion of HNO3 to PAN. This active production of PAN is the result of increased degradation of ethane in the stratosphere-troposphere mixed air mass to form CH3CHO, followed by subsequent formation of PAN under high NOx conditions. These findings imply that an adequate representation of stratospheric NOy input, in addition to stratospheric O3 influx, is essential to accurately simulate tropospheric Arctic O3, NOx and PAN in chemistry transport models. Plumes influenced by recent anthropogenic and biomass burning emissions observed during ARCTAS show highly elevated levels of hydrocarbons and NOy (mostly in the form of NOx and PAN), but do not contain O3 higher than that in the Arctic tropospheric background except some aged biomass burning plumes sampled during spring. Convection and/or lightning influences are negligible sources of O3 in the Arctic troposphere but can have significant impacts in the upper troposphere in the continental sub-Arctic during summer.

scholarly journals Uncertainties in modelling heterogeneous chemistry and Arctic ozone depletion in the winter 2009/2010

2013 ◽  
Vol 13 (8) ◽  
pp. 3909-3929 ◽  
Author(s):  
I. Wohltmann ◽  
T. Wegner ◽  
R. Müller ◽  
R. Lehmann ◽  
M. Rex ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Reaction Rate ◽  
Transport Model ◽  
Particle Number Density ◽  
Rate Coefficients ◽  
The Arctic ◽  
Number Density ◽  
Ozone Loss ◽  
Mixing Ratios ◽  
The Impact

Abstract. Stratospheric chemistry and denitrification are simulated for the Arctic winter 2009/2010 with the Lagrangian Chemistry and Transport Model ATLAS. A number of sensitivity runs is used to explore the impact of uncertainties in chlorine activation and denitrification on the model results. In particular, the efficiency of chlorine activation on different types of liquid aerosol versus activation on nitric acid trihydrate clouds is examined. Additionally, the impact of changes in reaction rate coefficients, in the particle number density of polar stratospheric clouds, in supersaturation, temperature or the extent of denitrification is investigated. Results are compared to satellite measurements of MLS and ACE-FTS and to in-situ measurements onboard the Geophysica aircraft during the RECONCILE measurement campaign. It is shown that even large changes in the underlying assumptions have only a small impact on the modelled ozone loss, even though they can cause considerable differences in chemical evolution of other species and in denitrification. Differences in column ozone between the sensitivity runs stay below 10% at the end of the winter. Chlorine activation on liquid aerosols alone is able to explain the observed magnitude and morphology of the mixing ratios of active chlorine, reservoir gases and ozone. This is even true for binary aerosols (no uptake of HNO3 from the gas-phase allowed in the model). Differences in chlorine activation between sensitivity runs are within 30%. Current estimates of nitric acid trihydrate (NAT) number density and supersaturation imply that, at least for this winter, NAT clouds play a relatively small role compared to liquid clouds in chlorine activation. The change between different reaction rate coefficients for liquid or solid clouds has only a minor impact on ozone loss and chlorine activation in our sensitivity runs.

scholarly journals Reactive nitrogen, ozone and ozone production in the Arctic troposphere and the impact of stratosphere-troposphere exchange

2011 ◽  
Vol 11 (4) ◽  
pp. 10721-10767 ◽  
Author(s):  
Q. Liang ◽  
J. M. Rodriguez ◽  
A. R. Douglass ◽  
J. H. Crawford ◽  
E. Apel ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Arctic Region ◽  
Tropospheric Chemistry ◽  
Ozone Production ◽  
The Arctic ◽  
Source Attribution ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The Impact

Abstract. We analyze the aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellite (ARCTAS) mission together with the GEOS-5 CO simulation to examine O3 and NOy in the Arctic and sub-Arctic region and their source attribution. Using a number of marker tracers and their probability density distributions, we distinguish various air masses from the background troposphere and examine their contribution to NOx, O3, and O3 production in the Arctic troposphere. The background Arctic troposphere has mean O3 of ~60 ppbv and NOx of ~25 pptv throughout spring and summer with CO decreases from ~145 ppbv in spring to ~100 ppbv in summer. These observed CO, NOx and O3 mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in the past two decades in processes that could have changed the Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses with mean O3 concentration of 140–160 ppbv are the most important direct sources of O3 in the Arctic troposphere. In addition, air of stratospheric origin is the only notable driver of net O3 formation in the Arctic due to its sustainable high NOx (75 pptv in spring and 110 pptv in summer) and NOy (~800 pptv in spring and ~1100 pptv in summer) levels. The ARCTAS measurements present observational evidence suggesting significant conversion of nitrogen from HNO3 to NOx and then to PAN (a net formation of ~120 pptv PAN) in summer when air of stratospheric origin is mixed with tropospheric background during stratosphere-to-troposphere transport. These findings imply that an adequate representation of stratospheric O3 and NOy input are essential in accurately simulating O3 and NOx photochemistry as well as the atmospheric budget of PAN in tropospheric chemistry transport models of the Arctic. Anthropogenic and biomass burning pollution plumes observed during ARCTAS show highly elevated hydrocarbons and NOy (mostly in the form of NOx and PAN), but do not contribute significantly to O3 in the Arctic troposphere except in some of the aged biomass burning plumes sampled during spring. Convection and/or lightning influences are negligible sources of O3 in the Arctic troposphere but can have significant impacts in the upper troposphere in the continental sub-Arctic during summer.

scholarly journals Characterization of Transport Regimes and the Polar Dome during Arctic Spring and Summer using in-situ Aircraft Measurements

2019 ◽  
Author(s):  
Heiko Bozem ◽  
Peter Hoor ◽  
Daniel Kunkel ◽  
Franziska Köllner ◽  
Johannes Schneider ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
High Arctic ◽  
The Arctic ◽  
Trace Gas ◽  
Second Phase ◽  
Aerosol Formation ◽  
Transport Barrier ◽  
Data Set ◽  
Air Masses ◽  
Mixing Ratios

Abstract. The springtime composition of the Arctic lower troposphere is to a large extent controlled by transport of mid-latitude air masses into the Arctic, whereas during the summer precipitation and natural sources play the most important role. Within the Arctic region, there exists a transport barrier, known as the polar dome, which results from sloping isentropes. The polar dome, which varies in space and time, exhibits a strong influence on the transport of air masses from mid-latitudes, enhancing it during winter and inhibiting it during summer. Furthermore, a definition for the location of the polar dome boundary itself is quite sparse in the literature. We analyzed aircraft based trace gas measurements in the Arctic during two NETCARE airborne field camapigns (July 2014 and April 2015) with the Polar 6 aircraft of Alfred Wegener Institute Helmholtz Center for Polar and Marine Research (AWI), Bremerhaven, Germany, covering an area from Spitsbergen to Alaska (134° W to 17° W and 68° N to 83° N). For the spring (April 2015) and summer (July 2014) season we analyzed transport regimes of mid-latitude air masses travelling to the high Arctic based on CO and CO2 measurements as well as kinematic 10-day back trajectories. The dynamical isolation of the high Arctic lower troposphere caused by the transport barrier leads to gradients of chemical tracers reflecting different local chemical life times and sources and sinks. Particularly gradients of CO and CO2 allowed for a trace gas based definition of the polar dome boundary for the two measurement periods with pronounced seasonal differences. For both campaigns a transition zone rather than a sharp boundary was derived. For July 2014 the polar dome boundary was determined to be 73.5° N latitude and 299–303.5 K potential temperature, respectively. During April 2015 the polar dome boundary was on average located at 66–68.5° N and 283.5–287.5 K. Tracer-tracer scatter plots and probability density functions confirm different air mass properties inside and outside of the polar dome for the July 2014 and April 2015 data set. Using the tracer derived polar dome boundaries the analysis of aerosol data indicates secondary aerosol formation events in the clean summertime polar dome. Synoptic-scale weather systems frequently disturb this transport barrier and foster exchange between air masses from midlatitudes and polar regions. During the second phase of the NETCARE 2014 measurements a pronounced low pressure system south of Resolute Bay brought inflow from southern latitudes that pushed the polar dome northward and significantly affected trace gas mixing ratios in the measurement region. Mean CO mixing ratios increased from 77.9 ± 2.5 ppbv to 84.9 ± 4.7 ppbv from the first period to the second period. At the same time CO2 mixing ratios significantly dropped from 398.16 ± 1.01 ppmv to 393.81 ± 2.25 ppmv. We further analysed processes controlling the recent transport history of air masses within and outside the polar dome. Air masses within the spring time polar dome mainly experienced diabatic cooling while travelling over cold surfaces. In contrast air masses in the summertime polar dome were diabatically heated due to insolation. During both seasons air masses outside the polar dome slowly descended into the Arctic lower troposphere from above caused by radiative cooling. The ascent to the middle and upper troposphere mainly took place outside the Arctic, followed by a northward motion. Our results demonstrate the successful application of a tracer based diagnostic to determine the location of the polar dome boundary.

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