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  • 1
    Online Resource
    Online Resource
    An Analysis of the Effect of Topography on the Martian Hadley Cells
    American Meteorological Society ; 2010
    In:  Journal of the Atmospheric Sciences Vol. 67, No. 3 ( 2010-03-01), p. 673-693
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 67, No. 3 ( 2010-03-01), p. 673-693
    Abstract: Previous work with Mars general circulation models (MGCMs) has shown that the north–south slope in Martian topography causes asymmetries in the Hadley cells at equinox and in the annual average. To quantitatively solve for the latitude of the dividing streamline and poleward boundaries of the cells, the Hadley cell model of Lindzen and Hou was modified to include topography. The model was thermally forced by Newtonian relaxation to an equilibrium temperature profile calculated with daily averaged solar forcing at constant season. Two sets of equilibrium temperatures were considered that either contained the effects of convection or did not. When convective effects were allowed, the presence of the slope component shifted the dividing streamline upslope, qualitatively similar to a change in season in Lindzen and Hou’s original (flat) model. The modified model also confirmed that the geometrical effects of the slope are much smaller than the thermal effects of the slope on the radiative–convective equilibrium temperature aloft. The results are compared to a simple MGCM forced by Newtonian relaxation to the same equilibrium temperature profiles, and the two models agree except at the winter pole near solstice. The simple MGCM results for radiative–convective forcing also show an asymmetry between the strengths of the Hadley cells at the northern summer and northern winter solstices. The Hadley cell weakens with increasing slope steepness at northern summer solstice but has little effect on the strength at northern winter solstice.
    Type of Medium: Online Resource
    ISSN: 1520-0469 , 0022-4928
    URL: Article
    DOI: 10.1175/2009JAS3130.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2010
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  • 2
    Online Resource
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    Mixing rates calculated from potential vorticity
    American Geophysical Union (AGU) ; 1988
    In:  Journal of Geophysical Research: Atmospheres Vol. 93, No. D5 ( 1988-05-20), p. 5221-5240
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 93, No. D5 ( 1988-05-20), p. 5221-5240
    Abstract: The flux and the gradient of potential vorticity are used to calculate horizontal mixing coefficients (K yy and K yz ). It is found that the mid‐latitude to polar mixing coefficients depend on the use of nongeostrophic winds. Geostrophic winds yield K yy values which are largely negative near the polar region, implying counter‐gradient transport of potential vorticity by eddies, while nongeostrophic winds yield K yy values which are mostly positive. Typically, large K yy values (in excess of 10 6 m 2 s −1 ) are found in the middle to upper stratosphere during winter in the northern hemisphere, the middle to upper stratosphere during spring in the southern hemisphere, and the troposphere for both northern and southern hemispheres. As an alternative procedure, K yy values have also been calculated using the momentum balance between the flux of potential vorticity and the residual circulation. These residual circulation balanced K yy values in the upper stratosphere are much larger than those determined from the potential vorticity fluxes and gradients. This difference may be a result of breaking gravity waves in the upper stratosphere and lower mesosphere.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/JD093iD05p05221
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1988
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    SSG: 16,13
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  • 3
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    Horizontal mixing coefficients for two‐dimensional chemical models calculated from National Meteorological Center data
    American Geophysical Union (AGU) ; 1986
    In:  Journal of Geophysical Research: Atmospheres Vol. 91, No. D7 ( 1986-06-20), p. 7919-7924
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 91, No. D7 ( 1986-06-20), p. 7919-7924
    Abstract: Calculations of the two‐dimensional species‐independent mixing coefficients for two‐dimensional chemical models for the troposphere and stratosphere are performed using quasi‐geostrophic potential vorticity fluxes and gradients from 4 years of National Meteorological Center data for the four seasons in both hemispheres. Results show that K yy values for the winter lower stratosphere are broadly consistent with those currently employed in two‐dimensional models, but K yy values in the northern winter upper stratosphere are much larger than those usually used.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/JD091iD07p07919
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1986
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  • 4
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    A model of the quasi-biennial oscillation on an equatorial beta-plane
    Wiley ; 1982
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 108, No. 456 ( 1982-04), p. 335-352
    Details
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 108, No. 456 ( 1982-04), p. 335-352
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    URL: Issue
    URL: Journal
    URL: Article
    DOI: 10.1002/qj.v108:456
    DOI: 10.1002/(ISSN)1477-870X
    DOI: 10.1002/qj.49710845604
    RVK:
    UA 1000
    RVK:
    UA 7650
    Language: English
    Publisher: Wiley
    Publication Date: 1982
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  • 5
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    Transformed Eulerian-Mean Theory. Part II: Potential Vorticity Homogenization and the Equilibrium of a Wind- and Buoyancy-Driven Zonal Flow
    American Meteorological Society ; 2005
    In:  Journal of Physical Oceanography Vol. 35, No. 2 ( 2005-02-01), p. 175-187
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 35, No. 2 ( 2005-02-01), p. 175-187
    Abstract: The equilibrium of a modeled wind- and buoyancy-driven, baroclinically unstable, flow is analyzed using the transformed Eulerian-mean (TEM) approach described in Part I. Within the near-adiabatic interior of the flow, Ertel potential vorticity is homogenized along mean isopycnals—a finding readily explained using TEM theory, given the geometry of the domain. The equilibrium, zonal-mean buoyancy structure at the surface is determined entirely by a balance between imposed surface fluxes and residual mean and eddy buoyancy transport within a “surface diabatic layer.” Balance between these same processes and the wind stress determines the stratification, and hence potential vorticity, immediately below this layer. Ertel potential vorticity homogenization below then determines the mean buoyancy structure everywhere. Accordingly, the equilibrium structure of this flow can be described—and quantitatively reproduced—from knowledge of the eddy mixing rates within the surface diabatic zone and the depth of this zone, together with potential vorticity homogenization beneath. These results emphasize the need to include near-surface buoyancy transport, as well as interior PV transport, in eddy parameterization schemes. They also imply that, in more realistic models, the surface buoyancy balances may be impacted by processes in remote locations that allow diapycnal flow.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO-2670.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
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  • 6
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    Online Resource
    Quantifying the Eddy Feedback and the Persistence of the Zonal Index in an Idealized Atmospheric Model
    American Meteorological Society ; 2009
    In:  Journal of the Atmospheric Sciences Vol. 66, No. 12 ( 2009-12-01), p. 3707-3720
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 66, No. 12 ( 2009-12-01), p. 3707-3720
    Abstract: An idealized atmospheric model is employed to quantify the strength of the eddy feedback and the persistence of the zonal index. The strength of the surface frictional damping on the zonal index is varied, and an external zonal momentum forcing is included to compensate for the momentum change associated with the friction change such that the climatological jet latitude and shape are unchanged. The model can generate a nearly identical climatology and leading mode of the zonal mean zonal wind for different frictional damping rates, except when the jet undergoes a regime transition. For those experiments without a regime transition, as the surface friction is increased, the strength of eddy feedback is enhanced but the zonal index becomes less persistent. A simple feedback model suggests that the e-folding decorrelation time scale of the zonal index can be determined by the frictional damping rate and the strength of eddy feedback. The strength of eddy feedback is found to be related to the instantaneous vertical wind shears near the surface controlled by the frictional damping. Furthermore, the climate response to an external zonal torque is proportional to the decorrelation time scale, although the simple prediction used here overestimates the climate response by a factor of 2.
    Type of Medium: Online Resource
    ISSN: 1520-0469 , 0022-4928
    URL: Article
    DOI: 10.1175/2009JAS3165.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
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  • 7
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    Online Resource
    On the meridional structure of long‐lived tropospheric constituents
    American Geophysical Union (AGU) ; 1988
    In:  Journal of Geophysical Research: Atmospheres Vol. 93, No. D12 ( 1988-12-20), p. 15897-15913
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 93, No. D12 ( 1988-12-20), p. 15897-15913
    Abstract: We consider the general problem of the meridional distribution and seasonal variability of long‐lived atmospheric constituents. Here “long‐lived” means that the time scale of the constituent exceeds the atmospheric exchange time across the region of interest. The relevant time scale is the “dynamic lifetime,” defined here as the ratio of the total atmospheric loading of the constituent to the total global source. Provided that this quantity is large (greater than about 5 years for the troposphere), the constituent attains a “gradient equilibrium” in which spatial gradients of mixing ratio are weak and the meridional and seasonal structure take on a form which, for a given source, is independent of the dynamic lifetime. Analysis of this structure involves clarification of the nature of atmospheric exchange processes and leads us to highlight thé nonuniqueness of such concepts as “interhemispheric exchange times.” These results are illustrated using a two‐dimensional transport model to conduct simulations of idealized long‐lived constituents with, in most cases, a simple mid‐latitude northern hemisphere source and a sink with uniform decay rate. It is suggested that these results will aid the synthesis of observations of long‐lived tropospheric constituents and will simplify the validation of transport models. More generally, this kind of approach might help to identify the effects of transport on trace constituent structures and thereby contribute to the understanding of the distributions of constituents which are not “long‐lived” in the sense used here.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/JD093iD12p15897
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1988
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    SSG: 16,13
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  • 8
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    Seasonal Variability of the Polar Stratospheric Vortex in an Idealized AGCM with Varying Tropospheric Wave Forcing
    American Meteorological Society ; 2015
    In:  Journal of the Atmospheric Sciences Vol. 72, No. 6 ( 2015-06-01), p. 2248-2266
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 72, No. 6 ( 2015-06-01), p. 2248-2266
    Abstract: The seasonal variability of the polar stratospheric vortex is studied in a simplified AGCM driven by specified equilibrium temperature distributions. Seasonal variations in equilibrium temperature are imposed in the stratosphere only, enabling the study of stratosphere–troposphere coupling on seasonal time scales, without the complication of an internal tropospheric seasonal cycle. The model is forced with different shapes and amplitudes of simple bottom topography, resulting in a range of stratospheric climates. The effect of these different kinds of topography on the seasonal variability of the strength of the polar vortex, the average timing and variability in timing of the final breakup of the vortex (final warming events), the conditions of occurrence and frequency of midwinter warming events, and the impact of the stratospheric seasonal cycle on the troposphere are explored. The inclusion of wavenumber-1 and wavenumber-2 topographies results in very different stratospheric seasonal variability. Hemispheric differences in stratospheric seasonal variability are recovered in the model with appropriate choices of wave-2 topography. In the model experiment with a realistic Northern Hemisphere–like frequency of midwinter warming events, the distribution of the intervals between these events suggests that the model has no year-to-year memory. When forced with wave-1 topography, the gross features of seasonal variability are similar to those forced with wave-2 topography, but the dependence on forcing magnitude is weaker. Further, the frequency of major warming events has a nonmonotonic dependence on forcing magnitude and never reaches the frequency observed in the Northern Hemisphere.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/JAS-D-14-0191.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
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  • 9
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    Forced Annular Mode Patterns in a Simple Atmospheric General Circulation Model
    American Meteorological Society ; 2007
    In:  Journal of the Atmospheric Sciences Vol. 64, No. 10 ( 2007-10-01), p. 3611-3626
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 64, No. 10 ( 2007-10-01), p. 3611-3626
    Abstract: Previous studies using simplified general circulation models have shown that “annular modes” arise as the dominant mode of variability. A simple GCM is used here to explore to what extent these modes are also the preferred response of the system to generic forcing. A number of trials are conducted under which the model is subjected to an artificial, zonally symmetric angular momentum forcing, and the climatologies of these trials are compared to that of the control. The forcing location is varied among the several trials. It is found that the changes in the model’s climatology are generally annular mode–like, as long as the imposed forcing projects strongly upon the annular modes of the unforced model. The role of changes to the eddy–zonal flow feedback versus the action of direct forcing is also considered through the use of a zonally symmetric version of the model. It is found that the direct responses to forcing are insufficient to capture either the strength or the structure of the annular mode responses. Instead, the changes in eddy fluxes are needed to produce the correct responses.
    Type of Medium: Online Resource
    ISSN: 1520-0469 , 0022-4928
    URL: Article
    DOI: 10.1175/JAS4031.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
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  • 10
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    Nonaxisymmetric Thermally Driven Circulations and Upper-Tropospheric Monsoon Dynamics
    American Meteorological Society ; 2000
    In:  Journal of the Atmospheric Sciences Vol. 57, No. 9 ( 2000-05), p. 1255-1276
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 57, No. 9 ( 2000-05), p. 1255-1276
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/1520-0469(2000)057〈1255:NTDCAU〉2.0.CO;2
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2000
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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