A study on the formation and trend of the Brewer-Dobson circulation

Okamoto, Kyosuke; Sato, K.; Akiyoshi, Hideharu

doi:10.1029/2010jd014953

Cited by 68 publications

(72 citation statements)

References 21 publications

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“…Planetary and synoptic-scale waves (and gravity waves in the Northern Hemisphere, e.g. Okamoto et al, 2011) contribute to this wave breaking region (McLandress and Shepherd, 2009). On the other hand, the deep circulation branch as found in this study is consistent with planetary-scale waves breaking in the middle stratosphere.…”

Section: Discussionmentioning

confidence: 99%

Residual circulation trajectories and transit times into the extratropical lowermost stratosphere

2011

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Abstract. Transport into the extratropical lowermost stratosphere (LMS) can be divided into a slow part (time-scale of several months to years) associated with the globalscale stratospheric residual circulation and a fast part (timescale of days to a few months) associated with (mostly quasi-horizontal) mixing (i.e. two-way irreversible transport, including extratropical stratosphere-troposphere exchange). The stratospheric residual circulation may be considered to consist of two branches: a deep branch more strongly associated with planetary waves breaking in the middle to upper stratosphere, and a shallow branch associated with synoptic and planetary scale waves breaking in the subtropical lower stratosphere. In this study the contribution due to the stratospheric residual circulation alone to transport into the LMS is quantified using residual circulation trajectories, i.e. trajectories driven by the (time-dependent) residual mean meridional and vertical velocities. This contribution represents the advective part of the overall transport into the LMS and can be viewed as providing a background onto which the effect of mixing has to be added. Residual mean velocities are obtained from a comprehensive chemistry-climate model as well as from reanalysis data. Transit times of air traveling from the tropical tropopause to the LMS along the residual circulation streamfunction are evaluated and compared to recent mean age of air estimates. A time-scale separation with much smaller transit times into the mid-latitudinal LMS than into polar LMS is found that is indicative of a separation of the shallow from the deep branch of the residual circulation. This separation between the shallow and the deep circulation branch is further manifested in a distinction in the aspect ratio Correspondence to: T. Birner (thomas@atmos.colostate.edu) of the vertical to meridional extent of the trajectories, the integrated mass flux along the residual circulation trajectories, as well as the stratospheric entry latitude of the trajectories. The residual transit time distribution reproduces qualitatively the observed seasonal cycle of youngest air in the extratropical LMS in fall and oldest air in spring.

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Section: Discussionmentioning

confidence: 99%

Residual circulation trajectories and transit times into the extratropical lowermost stratosphere

2011

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“…Note that, for hydrostatic flow m is always real, which means that all waves propagate vertically. Equation (21) already implies that the wave energy propagates upward, since the condition for the vertical component of the group velocity to be positive is that m and Uk + Vl have the same sign [50].…”

Section: Drag For Hydrostatic Flow With Constant Wind and Static Stabmentioning

confidence: 99%

“…The formation of polar stratospheric clouds, which have an important role in ozone depletion, is very sensitive to those temperatures [20], and therefore to the drag representation. Additionally, it has been shown recently that the Brewer-Dobson circulation in the stratosphere, which ascends at the tropics and descends at the poles, contributing to the transport of ozone and other chemical species, is partially driven by mountain waves, although its primary forcing is believed to be non-orographic gravity waves [21].…”

Section: Introductionmentioning

confidence: 99%

The physics of orographic gravity wave drag

Teixeira

2014

Front. Phys.

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The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations) to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.

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“…Together, both mechanisms constitute the total or Brewer-Dobson circulation (BDC), generally having an upward component at low latitudes and a return, downward component at the extratropical latitudes of both the Northern Hemisphere and the Southern Hemisphere (e.g., Butchart, 2014;Plumb, 2007;Haynes et al, 1991). The dissipation of planetary (or Rossby) waves and gravity wave forcings tends to accelerate the BDC and to enhance mixing in the winter hemisphere (e.g., Solomon et al, 1986;Plumb, 2007;Shepherd, 2007;Okamoto et al, 2011). Thus, it is likely that there is some asymmetry for the BDC in the Northern Hemisphere versus the Southern Hemisphere stratosphere because winter wave forcing and mixing processes are more pronounced and frequent in the Northern Hemisphere (Shepherd, 2007).…”

Section: Introductionmentioning

confidence: 99%

Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

Remsberg

2015

Atmos. Chem. Phys.

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Abstract. This study makes use of time series of methane (CH 4 ) data from the Halogen Occultation Experiment (HALOE) to detect whether there were any statistically significant changes of the Brewer-Dobson circulation (BDC) within the stratosphere during 1992-2005. The HALOE CH 4 profiles are in terms of mixing ratio versus pressure altitude and are binned into latitude zones within the Southern Hemisphere and the Northern Hemisphere. Their separate time series are then analyzed using multiple linear regression (MLR) techniques. The CH 4 trend terms for the Northern Hemisphere are significant and positive at 10 • N from 50 to 7 hPa and larger than the tropospheric CH 4 trends of about 3 % decade −1 from 20 to 7 hPa. At 60 • N the trends are clearly negative from 20 to 7 hPa. Their combined trends indicate an acceleration of the BDC in the middle stratosphere of the Northern Hemisphere during those years, most likely due to changes from the effects of wave activity. No similar significant BDC acceleration is found for the Southern Hemisphere. Trends from HALOE H 2 O are analyzed for consistency. Their mutual trends with CH 4 are anti-correlated qualitatively in the middle and upper stratosphere, where CH 4 is chemically oxidized to H 2 O. Conversely, their mutual trends in the lower stratosphere are dominated by their trends upon entry to the tropical stratosphere. Time series residuals for CH 4 in the lower mesosphere also exhibit structures that are anti-correlated in some instances with those of the tracer-like species HCl. Their occasional aperiodic structures indicate the effects of transport following episodic, wintertime wave activity. It is concluded that observed multi-year, zonally averaged distributions of CH 4 can be used to diagnose major instances of wave-induced transport in the middle atmosphere and to detect changes in the stratospheric BDC.

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A study on the formation and trend of the Brewer-Dobson circulation

Cited by 68 publications

References 21 publications

Residual circulation trajectories and transit times into the extratropical lowermost stratosphere

Residual circulation trajectories and transit times into the extratropical lowermost stratosphere

The physics of orographic gravity wave drag

Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

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