In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 8 ( 2019-04-26), p. 5511-5528
Abstract:
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 a
fixed lifetime and predominantly midlatitude land-based sources in models
participating in the Chemistry Climate Model Initiative (CCMI). We show that
there is a 25 %–45 % difference in the Arctic concentrations of this tracer
among the models. This spread is correlated with the spread in the location
of the Pacific jet, as well as the spread in the location of the Hadley Cell
(HC) edge, which varies consistently with jet latitude. Our results suggest
that it is likely that the HC-related zonal-mean meridional transport rather
than the jet-related eddy mixing is the major contributor to the inter-model
spread in the transport of land-based tracers into the Arctic. Specifically,
in models with a more northern jet, the 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 may result in differences in 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 both land and ocean, the inter-model
spread of this zonally uniform tracer is more related to variations in
parameterized convection over oceans rather than variations in HC extent,
particularly during boreal winter. This suggests that transport of land-based
and oceanic tracers or aerosols towards the Arctic differs in pathways and
therefore their corresponding inter-model variabilities result from different
physical processes.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-19-5511-2019
DOI:
10.5194/acp-19-5511-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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