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  • 1
    Online Resource
    Online Resource
    Superrotation of Titan’s Stratosphere Driven by the Radiative Heating of the Haze Layer
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 928, No. 2 ( 2022-04-01), p. 149-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 928, No. 2 ( 2022-04-01), p. 149-
    Abstract: Titan’s stratosphere has been observed in a superrotation state, where the atmosphere rotates many times faster than the surface does. Another characteristic of Titan’s atmosphere is the presence of a thick haze layer. In this paper, we performed numerical experiments using a general circulation model to explore the effects of the haze layer on the stratospheric superrotation. We employed a semigray radiation model of Titan’s atmosphere following McKay et al., which takes account of sunlight absorption by the haze particles. The phase change of methane or seasonal changes were not taken into account. Our model with radiation parameters tuned for Titan yielded a global eastward wind around the equator with larger velocities at higher altitudes, except at around 70 km, after 10 5 Earth days. Although the atmosphere is not in an equilibrium state, the zonal wind profiles are approximately consistent with the observed one. By changing the parameters of the radiation model, we found that the intensity and the location of the maximum zonal wind velocity highly depended on the optical thickness and the altitude of the haze layer, respectively. Analysis of our experiments suggests that the quasi-stationary stratospheric superrotation is maintained by the balance between the meridional circulation decoupled from the surface and the eddies that transport angular momentum equatorward. This is different from, but similar to, the so-called Gierasch mechanism, in which momentum is supplied from the surface. This structure may explain the no-wind region at about 80 km in altitude.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac54ab
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2960-9
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 2
    Online Resource
    Online Resource
    Significance of a Midlatitude SST Frontal Zone in the Formation of a Storm Track and an Eddy-Driven Westerly Jet*
    American Meteorological Society ; 2010
    In:  Journal of Climate Vol. 23, No. 7 ( 2010-04-01), p. 1793-1814
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 23, No. 7 ( 2010-04-01), p. 1793-1814
    Abstract: In a set of idealized “aquaplanet” experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature (SST) is prescribed globally as the lower boundary condition, an assessment is made of the potential influence of the frontal SST gradient upon the formation of a storm track and an eddy-driven midlatitude polar front jet (PFJ), and on its robustness against changes in the intensity of a subtropical jet (STJ). In experiments with the frontal midlatitude SST gradient as that observed in the southwestern Indian Ocean, transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the SST front with an enhanced low-level baroclinic growth of eddies. In the winter hemisphere, another storm track forms just below the intense STJ core, but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath. The near-surface westerlies are strongest near the midlatitude SST front as observed, consistent with westerly momentum transport associated with baroclinic eddy growth. The sharp poleward decline in the surface sensible heat flux across the SST frontal zone sustains strong near-surface baroclinicity against the relaxing effect by vigorous poleward eddy heat transport. Elimination of the midlatitude frontal SST gradient yields marked decreases in the activity of eddies and their transport of angular momentum into midlatitudes, in association with equatorward shifts of the PFJ-associated low-level westerlies and a subtropical high pressure belt, especially in the summer hemisphere. These impacts of the midlatitude frontal SST gradient are found to be robust against modest changes in the STJ intensity as observed in its interannual variability, suggesting the potential importance of midlatitude atmosphere–ocean interaction in shaping the tropospheric general circulation.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2009JCLI3163.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2010
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    detail.hit.zdb_id: 2021723-7
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  • 3
    Online Resource
    Online Resource
    The Aqua-Planet Experiment (APE): CONTROL SST Simulation
    Meteorological Society of Japan ; 2013
    In:  Journal of the Meteorological Society of Japan. Ser. II Vol. 91A, No. 0 ( 2013), p. 17-56
    Details
    In: Journal of the Meteorological Society of Japan. Ser. II, Meteorological Society of Japan, Vol. 91A, No. 0 ( 2013), p. 17-56
    Type of Medium: Online Resource
    ISSN: 0026-1165 , 2186-9057
    URL: Article
    DOI: 10.2151/jmsj.2013-A02
    Language: English
    Publisher: Meteorological Society of Japan
    Publication Date: 2013
    detail.hit.zdb_id: 241374-7
    SSG: 14
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  • 4
    Online Resource
    Online Resource
    The Earth Simulator Center
    Japan Agency for Marine-Earth Science and Technology ; 2009
    In:  JAMSTEC Report of Research and Development Vol. 9, No. 1 ( 2009), p. 1_75-1_135
    Details
    In: JAMSTEC Report of Research and Development, Japan Agency for Marine-Earth Science and Technology, Vol. 9, No. 1 ( 2009), p. 1_75-1_135
    Type of Medium: Online Resource
    ISSN: 1880-1153 , 2186-358X
    URL: Article
    DOI: 10.5918/jamstecr.9.1_75
    Language: Unknown
    Publisher: Japan Agency for Marine-Earth Science and Technology
    Publication Date: 2009
    detail.hit.zdb_id: 2901958-8
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  • 5
    Online Resource
    Online Resource
    Deep ocean inertia‐gravity waves simulated in a high‐resolution global coupled atmosphere–ocean GCM
    American Geophysical Union (AGU) ; 2008
    In:  Geophysical Research Letters Vol. 35, No. 4 ( 2008-02)
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 35, No. 4 ( 2008-02)
    Abstract: In order to investigate the deep ocean inertia‐gravity waves, a high‐resolution global coupled atmosphere–ocean simulation is carried out with a coupling interval of 20 minutes. Large (∼10 −3 m s −1 ) root‐mean‐square variability of vertical velocity is found in middepths (2000–4000 m), which is not reported in previous studies using realistic ocean simulations. Horizontal distribution of the large variability roughly corresponds to the wintertime atmospheric storm tracks and is stretched equatorward due to β ‐dispersion in open ocean with some “shadow regions” behind the obstacles. Frequency spectrum of vertical velocity has strong peaks at around f and 2 f ( f is the local inertial period) in midlatitudes, and has additional peak at around (3/2) f or 3 f at some points. These results suggest necessity of re‐evaluation of wind‐induced near‐inertial energy with high‐frequency atmospheric forcing.
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2007GL032807
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2008
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 6
    Online Resource
    Online Resource
    Explicit global simulation of the mesoscale spectrum of atmospheric motions
    American Geophysical Union (AGU) ; 2006
    In:  Geophysical Research Letters Vol. 33, No. 12 ( 2006-06)
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 33, No. 12 ( 2006-06)
    Abstract: The horizontal spectrum of kinetic energy in the upper troposphere in experiments conducted with the Atmospheric GCM for the Earth Simulator (AFES) global spectral general circulation model is examined. We find that the control version of AFES run at T639 spectral resolution can simulate a realistic kinetic energy spectrum with roughly −3 power‐law dependence on horizontal wavenumber for wavelengths between about 5000 and 500 km, transitioning to a shallower mesoscale regime at smaller wavelengths. The results depend to a degree on the magnitude of the parameterized horizontal hyperdiffusion, but the existence of a distinct shallow mesoscale range in the simulations is independent of the hyperdiffusion employed. We present results from a number of AFES integrations with spectral truncations ranging from T39 to T639 and determine the appropriate scaling of the parametrized hyperdiffusion with model numerical resolution so that the kinetic energy spectrum in each case converges to realistic values. The experiment was also repeated in a dry version of the model. This version also simulated a shallow mesoscale range, supporting the view that the mesoscale regime in the atmosphere is energized, at least in part, by a predominantly downscale nonlinear spectral cascade.
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2006GL026429
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2006
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 7
    Online Resource
    Online Resource
    High resolution simulations of atmospheric and oceanic circulation
    American Geophysical Union (AGU) ; 2006
    In:  Eos, Transactions American Geophysical Union Vol. 87, No. 18 ( 2006-05-02), p. 176-176
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 87, No. 18 ( 2006-05-02), p. 176-176
    Abstract: The pursuit of fine spatial representation in models of the atmospheric and oceanic circulation has been a theme running through the development of the field of numerical simulation. For example, in studies of the global ocean circulation, a longstanding concern has been the issue of adequately resolving particularly energetic eddies, such as Gulf Stream rings. In global and regional atmospheric models, a key issue has been resolving mesoscale circulations that organize clouds and convection. With the recent advent of a new generation of high‐performance computing systems, such as the Japan Agency for Marine‐Earth Science and Technology's (JAMSTEC) Earth Simulator, some notable thresholds in terms of model resolution have been approached or, in some cases, surpassed. For example, the first long integrations with genuine eddy‐resolving global ocean models were reported in 2003. On the atmospheric side, decadal integrations with global models with effective horizontal resolution of approximately 20 kilometers have now become possible, and very short integrations of models that explicitly resolve scales approaching those of individual convective elements were first reported in 2005. These developments in global models have been paralleled by rising research activity with increasingly fine resolution regional atmospheric models for climate and shortrange forecasting applications.
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/2006EO180010
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2006
    detail.hit.zdb_id: 2118760-5
    detail.hit.zdb_id: 240154-X
    SSG: 16,13
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  • 8
    Online Resource
    Online Resource
    Planetary-scale streak structure reproduced in high-resolution simulations of the Venus atmosphere with a low-stability layer
    Springer Science and Business Media LLC ; 2019
    In:  Nature Communications Vol. 10, No. 1 ( 2019-01-09)
    Details
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 10, No. 1 ( 2019-01-09)
    Abstract: Cloud patterns are important clues for revealing the atmospheric circulation of Venus. Recently, a planetary-scale streak structure has been discovered in middle- and lower-cloud images of Venus’ night-side taken by IR2, the 2-μm camera, on board the Akatsuki orbiter. However, its formation mechanism has not been investigated. Here we succeed, for the first time, in reproducing the patterns of the observed streak structure, as regions of strong downward flows that develop in high-resolution global simulations of the Venus atmosphere. The streaks are formed in both hemispheres with equatorial symmetry, which is caused by equatorial Rossby-like and Kelvin-like waves with zonal wavenumber one. The low-stability layer that has been suggested by past observations is essential for reproducing the streak structure. The streaks of downward flow result from the interaction of the meridionally tilted phase lines of the Rossby-like waves and the characteristics of baroclinic instability produced around the low-stability layer.
    Type of Medium: Online Resource
    ISSN: 2041-1723
    URL: Article
    DOI: 10.1038/s41467-018-07919-y
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2019
    detail.hit.zdb_id: 2553671-0
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  • 9
    Online Resource
    Online Resource
    Mesoscale spectrum of atmospheric motions investigated in a very fine resolution global general circulation model
    American Geophysical Union (AGU) ; 2008
    In:  Journal of Geophysical Research: Atmospheres Vol. 113, No. D18 ( 2008-09-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 113, No. D18 ( 2008-09-27)
    Abstract: The horizontal spectrum of wind variance, conventionally referred to as the kinetic energy spectrum, is examined in experiments conducted with the Atmospheric GCM for the Earth Simulator (AFES) global spectral general circulation model. We find that the control version of AFES run at T639 horizontal spectral resolution simulates a kinetic energy spectrum that compares well at large scales with global observational reanalyses and, at smaller scales, with available aircraft observations at near‐tropopause levels. Specifically there is a roughly −3 power‐law dependence on horizontal wave number for wavelengths between about 5000 and 500 km, transitioning to a shallower mesoscale regime at smaller wavelengths. This is seen for both one‐dimensional spectra and for the two‐dimensional total wave number spectrum based on a spherical harmonic analysis. The simulated spectrum at midtropospheric levels is similar in that there is a transition to a shallower mesoscale regime, but the spectrum in the mesoscale is clearly steeper at midtroposphere than near the tropopause. There seem to be no extensive observations of horizontal spectra available in the midtroposphere, so it is not known whether the contrast seen in the model between upper and mid tropospheric levels is realistic. The dependence of the model simulated variability on the subgrid‐scale moist convection parameterization is examined. The space‐time variability of rainfall is shown to depend strongly on the convection scheme employed. The tropospheric kinetic energy spectrum in the mesoscale seems to be correlated with the precipitation behavior, so that in a version with a more variable precipitation field the kinetic energy in the mesoscale is enhanced. This suggests that the mesoscale motions in the model may be directly forced to a significant extent by the variability in the latent heating field. Experiments were also performed with a dry dynamical core version of the model run at both T639 and T1279 resolutions. This version also simulated a shallow mesoscale range, supporting the view that the mesoscale regime in the atmosphere is energized, at least in part, by a predominantly forward (i.e., downscale) nonlinear spectral cascade. Experiments with various formulations of the hyperdiffusion horizontal mixing parameterization show that the kinetic energy spectrum over about the last half of the resolved wave number range is under strong control by the parameterized mixing. However, the T1279 model simulates almost a decade of the shallow mesoscale regime (i.e., for horizontal wavelengths from about 80 to 500 km) that appears to be fairly independent of the diffusion employed. Finally, experiments are conducted in the dry version to see the effects on the kinetic energy spectrum of changing the thermal Rossby number for the simulations.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2008JD009785
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2008
    detail.hit.zdb_id: 161666-3
    SSG: 16,13
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  • 10
    Online Resource
    Online Resource
    “Virtual” Atmospheric and Oceanic Circulation in the Earth Simulator
    American Meteorological Society ; 2007
    In:  Bulletin of the American Meteorological Society Vol. 88, No. 6 ( 2007-06-01), p. 861-866
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 88, No. 6 ( 2007-06-01), p. 861-866
    Abstract: High-resolution simulations of the atmospheric and oceanic general circulations on the Earth Simulator are briefly introduced to a wider research and educational community. Some early results have been published and are reviewed in this article. The high-resolution simulations may have more information in certain aspects than observations while the simulations need to be validated. On the other hand, high-resolution observations in which uncertainties are unavoidable are now available. Possible close collaboration between observational and simulation research is proposed.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-88-6-861
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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