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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Aug 2018

Research article | 30 Aug 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Large-scale transport into the Arctic: the roles of the midlatitude jet and the Hadley Cell

Huang Yang1, Darryn W. Waugh1,2, Clara Orbe3, Guang Zeng4, Olaf Morgenstern4, Douglas E. Kinnison5, Jean-Francois Lamarque5, Simone Tilmes5, David A. Plummer6, Patrick Jöckel7, Susan E. Strahan8,9, Kane A. Stone10,11,a, and Robyn Schofield10,11 Huang Yang et al.
  • 1Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland, USA
  • 2School of Mathematics, University of New South Wales, Sydney, Australia
  • 3NASA Goddard Institute for Space Studies, New York, New York, USA
  • 4National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 5National Center for Atmospheric Research (NCAR), Atmospheric Chemistry Observations and Modeling (ACOM) Laboratory, Boulder, Colorado, USA
  • 6Climate Research Branch, Environment and Climate Change Canada, Montreal, QC, Canada
  • 7Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 8Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 9Universities Space Research Association, Columbia, Maryland, USA
  • 10School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia
  • 11ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales 2052, Australia
  • anow at: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA

Abstract. Transport from the Northern Hemisphere (NH) midlatitudes to the Arctic plays a crucial role in determining the abundance of trace gases and aerosols that are important to Arctic climate via impacts on radiation and chemistry. Here we examine this transport using an idealized tracer with fixed lifetime and predominantly midlatitude land-based sources in models participating in the Chemistry Climate Model Initiative (CCMI). We show that there is a 20%–40% difference in the Arctic concentrations of this tracer among the models. This spread is found to be generally related to the spread in location of the Pacific jet, with lower Arctic tracer concentrations occurring in models with a more northern jet, during both winter and summer. However, the underlying mechanism for this relationship does not involve the jet directly, but instead involves differences in the surface meridional flow over the tracer source region, that vary with jet latitude. Specifically, in models with a more northern jet, the Hadley Cell (HC) generally extends further north and the tracer source region is mostly covered by surface southward flow associated with the lower branch of the HC, resulting in less efficient transport poleward to the Arctic. During boreal summer, there are poleward biases in jet location in free-running models, and these models likely underestimate the rate of transport into the Arctic. Models using specified dynamics do not have biases in the jet location, but do have biases in the surface meridional flow, which results in differences in the transport into the Arctic. In addition to the land-based tracer, the midlatitude-to-Arctic transport is further examined by another idealized tracer with zonally uniform sources. With equal sources from lands and oceans, the intermodel spread of this zonally uniform tracer is more related to variations of parameterized convection over oceans than variations of HC extent particularly during boreal summer. This suggests that transport of land-based and oceanic tracers or aerosols towards the Arctic differ in pathways and therefore their corresponding intermodel variabilities result from different physical processes.

Huang Yang et al.
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Status: final response (author comments only)
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Huang Yang et al.
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Short summary
We evaluate the performance of a suite of models in simulating the large-scale transport from the northern midlatitudes to the Arctic using a CO-like idealized tracer. We find a large multi-model spread of the Arctic concentration of this CO-like tracer which is well correlated with the differences in the location of midlatitude jet as well as the northern Hadley Cell edge. Our results suggest Hadley Cell is the key and zonal-mean transport by surface meridional flow needs better constraint.
We evaluate the performance of a suite of models in simulating the large-scale transport from...