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  • 1
    Publikationsdatum: 2017-01-01
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2017-08-30
    Beschreibung: With the Weather Research and Forecasting (WRF) Model specifically configured to simulate the intensification and evolution of an extratropical baroclinic wave, this study first investigates why cold fronts are characteristically longer, narrower, and more intense than warm fronts in the extratropical atmosphere. It is found that the differential thermal advection by the geostrophic and ageostrophic wind components in the two frontal regions results in a greater thermal contrast across the cold front. The length of the cold front is essentially the length scale of the intensifying baroclinic wave (i.e., on the order of radius of deformation). The frontal system as a whole moves eastward under the influence of a steering flow. In addition, the cold front outpaces the warm front eastward, making the western portion of the warm front progressively occluded and the eastern portion of the warm front shorter. The dynamical processes tend to move the cold front eastward, whereas the diabatic heating processes tend to move it westward, contributing to the narrowness of the cold front. This study also investigates whether, how, and why an upper-level front (ULF) would synergistically interact with a surface front (SF). It is found that a favorable circumstance for such interaction to occur in an observed extratropical cyclone and in the WRF Model simulation is when the ULF and SF are roughly parallel to one another with the ULF aloft located a few hundred kilometers to the west of the SF. The relative importance of “forcing” for the ageostrophic circulation associated with the geostrophic circulation, diabatic heating, and friction are diagnosed in such interaction.
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2016-06-24
    Beschreibung: This paper reports a diagnosis of the structure and dynamics of upper-level fronts (ULFs) simulated with a high-resolution Weather Research and Forecasting Model with diabatic heating versus one without diabatic heating. The ULFs of both simulations develop in about 6 days as integral parts of intensifying baroclinic waves. Each has a curvilinear structure along the southern edge of a relatively narrow long tongue of high potential vorticity in which stratospheric air is subducted to different tropospheric levels by synoptic-scale subsidence. It resembles a veil in the sky of varying thickness across the midsection upstream of the trough of the baroclinic wave. The 3D frontogenetical function is shown to be a necessary and sufficient metric for quantifying the rate of development of ULFs. Its value is mostly associated with the contribution of the 3D ageostrophic velocity component. Upper-level frontogenesis is attributable to the joint direct influence of the vortex-stretching process and the deformation property of the 3D ageostrophic flow component. The model also generates a spectrum of vertically propagating mesoscale gravity waves. The ULFs simulated with and without diabatic heating processes are qualitatively similar. The ULF is considerably more intense when there is heating. The heating, however, does not make a significant direct contribution to but indirectly does so through its impacts on the subsidence field of the baroclinic wave.
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Monographie ausleihbar
    Monographie ausleihbar
    Cambridge [u.a.] : Cambridge Univ. Press
    Signatur: AWI A6-12-0035
    Beschreibung / Inhaltsverzeichnis: Contents: 1. Fundamental concepts and physical laws. - 2. Basic approximations and elementary flows. - 3. Vorticity and potential vorticity dynamics. - 4. Friction and boundary layers. - 5. Fundamentals of wave dynamics. - 6. Quasi-geostrophic theory and two-layer model. - 7. Dynamic adjustment. - 8. Instability theories. - 9. Stationary planetary wave dynamics. - 10. Wave-mean flow interaction. - 11. Equilibration dynamics of baroclinic waves. - 12. Nongeostrophic dynamics.
    Beschreibung / Inhaltsverzeichnis: Atmospheric dynamics is a core component of all atmospheric science curricula. It is concerned with how and why different classes of geophysical disturbances form, what dictates their structure and movement, how the Earth's uneven surface impacts with them, how they evolve to mature stage, how they interact with the background flow, how they decay and how they collectively constrain the general circulation of the atmosphere. Mankin Mak's new textbook provides a self-contained course on atmospheric dynamics. The first half of the book is suitable for undergraduates, and develops the physical, dynamical and mathematical concepts at the fundamental level. The second half of the book is aimed at more advanced students who are already familiar with the basics. The concepts have been developed from many years of the author's teaching at the University of Illinois. The discussions are supplemented with schematics, weather maps and statistical plots of the atmospheric gerneral circulation. Students often find the connection between theoretical dynamics and atmospheric observation somewhat tenuous, and this book demonstrates strong connection between the key dynamics and real observations in the atmosphere, with many illustrative analyses in the simplest possible model settings. Physical reasoning is shown to be even more crucial than mathematical skill in tackling dynamical problems. This textbook is an invaluable asset for courses in atmospheric dynamics for undergraduates as well as for graduate studentes and researchers in atmospheric science, ocean science, weather forecasting, environmental science and applied mathematics. Some background in mathematics and physics is assumed.
    Materialart: Monographie ausleihbar
    Seiten: XIV, 486 S. : Ill., graph. Darst., Kt.
    Ausgabe: 1. publ.
    ISBN: 9780521195737
    Zweigbibliothek: AWI Bibliothek
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2007-04-01
    Print ISSN: 0377-0265
    Digitale ISSN: 1872-6879
    Thema: Geographie , Geologie und Paläontologie , Physik
    Publiziert von Elsevier
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2006-10-01
    Beschreibung: On the basis of an intraseasonal variability index of storm track evaluated for 40 winters (1963–64 through 2003–04) of NCEP–NCAR reanalysis data, it is found that well-defined midwinter minimum [MWMIN; (midwinter maximum MWMAX)] occurs in 21 (8) winters over the North Pacific. In contrast, MWMIN (MWMAX) occurs in 4 (25) of the 40 winters over the North Atlantic. The power spectrum of such an index for the Pacific has a broad peak between 5 and 10 yr, whereas the spectrum of the index for the Atlantic has comparable power in two spectral bands: 2–2.8 and 3.5–8 yr. Over the North Pacific, the increase in the zonal asymmetry of the background baroclinicity as well as in the corresponding horizontal deformation of the time-mean jet from early/late winter to midwinter is distinctly larger in an MWMIN winter. Associated with these changes, there is a distinctly stronger barotropic damping rate in the January of an MWMIN winter. The increase in the net conversion rate of eddy kinetic energy from early/late winter to midwinter is much larger in an MWMAX winter than that in an MWMIN winter. Even though there is a modest increase in the barotropic damping from early/late winter to midwinter over the North Atlantic, it is overcompensated by a larger increase in the baroclinic conversion rate. That would result in MWMAX. These results are empirical evidences in support of a hypothesis that a significant enhancement of the barotropic damping relative to the baroclinic growth from early/late winter to midwinter is a major contributing factor to MWMIN of the Pacific storm track.
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2005-04-01
    Beschreibung: The synoptic variability of a two-level quasigeostrophic flow in response to plausible changes in the forcing of a localized baroclinic jet is investigated in the context of the midwinter minimum of the Pacific storm track (MWM). The changes in the model forcing are introduced in terms of a reference potential vorticity field that is associated with plausible changes in the global baroclinicity, zonal variation of the baroclinicity, and horizontal deformation over the Pacific from early winter to midwinter conditions. It is found that the modal instability growth rate of perturbation in such a localized jet is significantly reduced in spite of an increase in the local baroclinicity. The dynamical nature of such an effect can be interpreted as a generalized barotropic governor effect on localized baroclinic instability. The existence of three instability regimes is established on the basis of energetics characteristics. The intensity of the nonlinear model storm track is reduced by about 30% in response to a change in the forcing condition from early to midwinter. The characteristics of the linear model storm track and nonlinear model storm track are compared. The overall results support a hypothesis that MWM could stem from a sufficiently large increase in the stabilizing influence of the local barotropic process in spite of a simultaneous increase in its local baroclinicity in the Pacific jet from early to midwinter.
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2002-02-01
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2001-07-01
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2000-02-01
    Print ISSN: 0022-4928
    Digitale ISSN: 1520-0469
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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