The role of monsoon‐like zonally asymmetric heating in interhemispheric transport

Chen, Gang; Orbe, Clara; Waugh, Darryn W.

doi:10.1002/2016jd026427

Cited by 12 publications

(24 citation statements)

References 53 publications

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“…The sum of advection (Figure g) and eddy transport (Figure h) is very similar to the resolved dynamics term (Figure f) (not shown). While advection plays a significant role in the deep tropics in carrying the tracer across the equator (e.g., Chen et al, ; Orbe et al, ), the eddy transport dominates in the NH upper troposphere and high latitude middle‐to‐lower troposphere. We further decompose the eddy transport term into the meridional divergence term (Figure i) and the vertical divergence term (Figure j).…”

Section: Resultsmentioning

confidence: 99%

Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer

Orbe

Tilmes

et al. 2020

JGR Atmospheres

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This study identifies the fast (i.e., ∼ days-weeks) transport pathways that connect the Northern Hemisphere surface to the upper troposphere and lower stratosphere (UTLS) during northern summer by integrating a large (90 member) ensemble of Boundary Impulse Response tracers in the Whole Atmosphere Community Climate Model version 5. We show that there is a fast transport pathway that occurs over the southern slope of the Tibetan Plateau, northern India, the Arabian Sea, and Saudi Arabia; furthermore, we show that during July this pathway connects the Northern Hemisphere surface to the UTLS on a modal time scale of 5-10 days. A less efficient transport pathway is also identified over the western Pacific. A detailed budget analysis reveals that, while convective processes are responsible for transport to 200-300 hPa, the resolved dynamics, specifically the vertical eddy flux, dominate at 100-150 hPa. Transport variations are analyzed on weekly, monthly, and interannual time scales and are largely related to differences in the resolved dynamics in the UTLS.

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Section: Resultsmentioning

confidence: 99%

Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer

Orbe

Tilmes

et al. 2020

JGR Atmospheres

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“…Orbe et al (2012) computed the mean age of air using the transit-time distribution, a more detailed description of atmospheric transport pathways (Hall and Plumb, 1994), and Orbe et al (2013) studied the effect of a changing climate on tropospheric transport through an analysis of air mass origins. Chen et al (2017) used the age to study the role of monsoon-induced eddy circulation in inter-hemispheric transport of tracers in a HS94 dry atmospheric model and Waugh et al (2019) even used age to estimate the transport time-scales in the Martian atmosphere.…”

Section: Stratospheric Transport and The Age-of-airmentioning

confidence: 99%

Numerical impacts on tracer transport: A proposed intercomparison test of Atmospheric General Circulation Models

Gupta

Gerber

Lauritzen

2020

Quart J Royal Meteoro Soc

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The transport of trace gases by the atmospheric circulation plays an important role in the climate system and its response to external forcing. Transport presents a challenge for Atmospheric General Circulation Models (AGCMs), as errors in both the resolved circulation and the numerical representation of transport processes can bias their abundance. In this study, two tests are proposed to assess transport by the dynamical core of an AGCM. To separate transport from chemistry, the tests focus on the age-of-air, an estimate of the mean transport time by the circulation. The tests assess the coupled stratosphere-troposphere system, focusing on transport by the overturning circulation and isentropic mixing in the stratosphere, or Brewer-Dobson Circulation, where transport timescales on the order of months to years provide a challenging test of model numerics. Four dynamical cores employing different numerical schemes (finite-volume, pseudo-spectral, and spectral-element) and discretizations (cubed sphere versus latitude-longitude) are compared across a range of resolutions. The subtle momentum balance of the tropical stratosphere is sensitive to model numerics, and the first intercomparison reveals stark differences in tropical stratospheric winds, particularly at high vertical resolution: some cores develop westerly jets and others easterly jets. This leads to substantial spread in transport, biasing the age-of-air by up to 25% relative to its climatological mean, making it difficult to assess the impact of the numerical representation of transport processes. This uncertainty is removed by constraining the tropical winds in the second intercomparison test, in a manner akin to specifying the Quasi-Biennial Oscillation in an AGCM. The dynamical cores exhibit qualitative agreement on the structure of atmospheric transport in the second test, with evidence of convergence as the horizontal and vertical resolution is increased in a given model. Significant quantitative differences remain, however, particularly between models employing spectral versus finite-volume numerics, even in state-of-the-art cores. K E Y W O R D S age of air, Brewer-Dobson circulation, dynamical cores, stratospheric dynamics, tracer transport. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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“…However, the zonal variations of the mixing ratio between 20 • N and 40 • N differs between the tracers: For one tracer, referred to as the zonally symmetric (ZS) tracer, the surface mixing ratio is fixed at 1 mol/mol for all longitudes, whereas for the other tracer, the zonally asymmetric (ZA) tracer, the surface mixing ratio is fixed at 1 mol/mol only between 100-130 • E. Comparison between the two tracers isolates the importance of the longitudinal distribution of tracer source for the transport to the Arctic. Since the tracers have a prescribed loss we do not include a global tracer-mass fixer (as was included in Chen et al, 2017). All simulations are integrated for 10 years.…”

Section: 1029/2020gl090133mentioning

confidence: 99%

“…We perform tracer simulations using the Geophysical Fluid Dynamical Laboratory (GFDL) spectral atmospheric dynamical core, which solves the dry primitive equations on the sphere with Newtonian relaxation toward a prescribed equilibrium temperature and Rayleigh friction in the planetary boundary layer (see Held & Suarez, 1994, for details). The model is run at T42 horizontal resolution with 20 equally spaced sigma levels between

σ = 0.05

and 1 (Chen et al, 2017). All model output are further interpolated into an isobaric coordinate with 23 ERA‐40 levels to facilitate a more accurate flux calculation.…”

Section: Models and Simulationsmentioning

confidence: 99%

“…To examine the poleward transport in the different atmospheric flows, tracers are included in the simulations as in Chen et al (2017) with a semi‐Lagrangian scheme for horizontal advection (Lin et al, 1994), a finite‐volume parabolic scheme for vertical advection, and no explicit numerical diffusion. For each of the different flows, we include two tracers.…”

Section: Models and Simulationsmentioning

confidence: 99%

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Dependence of Atmospheric Transport Into the Arctic on the Meridional Extent of the Hadley Cell

Yang

Waugh

Orbe

et al. 2020

Geophysical Research Letters

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Recent studies have shown a large spread in the transport of atmospheric tracers into the Arctic among a suite of chemistry climate models and have suggested that this is related to the spread in the meridional extent of the Hadley Cell (HC). Here we examine the HC-transport relationship using an idealized model, where we vary the mean circulation and isolate its impact on transport to the Arctic. It is shown that the poleward transport depends on the relative position between the northern edge of the HC and the tracer source, with maximum transport occurring when the HC edge lies near the middle of the source region. Such dependence highlights the critical role of near-surface transport by the Eulerian mean circulation rather than eddy mixing in the free troposphere and suggests that variations in the HC edge and the tracer source region are both important for modeling Arctic composition. Plain Language Summary Long-range transport plays a crucial role in determining the distribution of pollutants in the Arctic, as many pollutants have their sources in northern middle latitudes. Recent studies show large differences in transport into the Arctic among models, and it has been suggested that this is related to differences in the northern edge of the Hadley Cell (HC) in the models. We revisit this topic using an idealized model in which the extent of the HC can be varied in a controlled manner. We show that the relative position between the tracer source and the northern edge of the HC plays an important role in determining how rapidly air is transported into the Arctic. The most rapid transport occurs when the HC edge lies near the middle of the tracer source region. This results suggest that variations in the HC edge and the tracer source region are both important for modeling Arctic composition. There is, unfortunately, large uncertainty in the simulated transport of tracers into the Arctic. This is highlighted by the very large multimodel spread in the simulated Arctic mixing ratios of carbon monoxide CO and black carbon (Shindell et al., 2008) and idealized tracers (with simplified chemistry highlighting variations only in the transport) (Orbe et al., 2018; Yang et al., 2019) from ensembles of chemistry transport or chemistry-climate models. The causes of these intermodel differences are not known and represent a major uncertainty in projections of changes in Arctic atmospheric composition. Atmospheric transport of energy, moisture, and trace gases is often decomposed into a component due to the mean meridional circulation (MMC) and a component due to eddy mixing. Many previous studies have shown that eddy mixing dominates the climatological-mean transport into the Arctic (

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The role of monsoon‐like zonally asymmetric heating in interhemispheric transport

Cited by 12 publications

References 53 publications

Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer

Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer

Numerical impacts on tracer transport: A proposed intercomparison test of Atmospheric General Circulation Models

Dependence of Atmospheric Transport Into the Arctic on the Meridional Extent of the Hadley Cell

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