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Discussion papers
https://doi.org/10.5194/acp-2019-70
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-70
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Feb 2019

Research article | 12 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

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

Heiko Bozem1, Peter Hoor1, Daniel Kunkel1, Franziska Köllner1,2, Johannes Schneider2, Andreas Herber3, Hannes Schulz3, W. Richard Leaitch4, Amir A. Aliabadi5, Megan D. Willis6,a, Julia Burkart6,b, and Jonathan P. D. Abbatt6 Heiko Bozem et al.
  • 1Johannes Gutenberg University of Mainz, Institute for Atmospheric Physics, Mainz, Germany
  • 2Particle Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 3Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 4Environment and Climate Change Canada, Toronto, Canada
  • 5School of Engineering, University of Guelph, Guelph, ON, Canada
  • 6Department of Chemistry, University of Toronto, Toronto, Canada
  • anow at: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
  • bnow at: University of Vienna, Aerosol Physics & Environmental Physic, Vienna, Austria

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.

Heiko Bozem et al.
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Short summary
We present airborne trace gas measurements in the European and Canadian Arctic for July 2014 and April 2015. Based on CO and CO2 in-situ data as well as 10-day kinematic back trajectories we characterize the prevailing transport regimes and derive a tracer based diagnostic for the determination of the polar dome boundary. Using the tracer derived boundary the analysis of the recent transport history of air masses within the polar dome reveals significant differerences between spring and summer.
We present airborne trace gas measurements in the European and Canadian Arctic for July 2014 and...
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