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  • Author or Editor: V. M. Gryanik x
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S. Danilov
and
V. M. Gryanik

Abstract

The problem of quantification of barotropic beta-plane turbulence driven by small-scale stochastic forcing into regimes dominated by quasi-periodic zonal jets is revisited. It is shown that the large-scale relative vorticity in such regimes is organized into a sequence of zonal bands. Its zonal mean profile varies approximately linearly within the bands. Its mean negative slope β∗ is less than the meridional gradient of the Coriolis parameter β, and depends on the external parameters (friction, forcing, and β). The neighboring bands are connected through the vorticity fronts where the zonal mean meridional gradient is large and positive.

The frontal-band vorticity structure defines piecewise parabolic profiles of asymmetric eastward and westward jets, and strong peaks in the low-k interval of turbulent zonal energy spectra, which store most of the zonal energy. The slope of their envelope depends on the structure of the frontal zones and is always steeper than −4. The presence of peaks invalidates the recent hypothesis on the universal power-law scaling E z (k) = C z β 2 k −5, C z = O(1), for the zonal energy spectra of beta-plane turbulence in strongly anisotropic regimes.

The power-law intervals could appear at large k and are linked to uncorrelated fluctuations of band profiles. It is shown that they could contain a part that slopes close to −5. However, its C z is not universal and depends on the external parameters.

A simple kinematic model of multijet beta-plane flows is proposed that explains the shape of the coherent part of zonal energy spectra and asymmetry between westward and eastward jets generated by vorticity bands, and quantifies the zonal wavenumber of jets k j in terms of the ratio of zonal enstrophy to zonal energy.

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S. D. Danilov
,
V. M. Gryanik
, and
D. J. Olbers

Abstract

The authors investigate the spreading stage of the deep ocean convection for a strip-shaped convective region to study the law of spreading and sensitivity of the eddy exchange efficiency parameter to the shape of the region and the background stratification. To simulate this convection process a two-layer quasigeostrophic model is used and the input of buoyancy due to surface cooling is parameterized through creation of pairs of baroclinic point vortices with opposite signs of potential vorticity (hetons) at a constant rate. It is shown that the eddy exchange efficiency parameter for lateral fluxes of potential density out of the convective region is not universal but essentially depends on the shape of the region and the relative layer thicknesses. The horizontal spreading of the potential density anomaly shows a faster than diffusive, quasi-linear dependence on time at moderate values of the surface buoyancy flux. This behavior is due to the specific dynamics of hetons and heton clusters.

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S. Zilitinkevich
,
V. M. Gryanik
,
V. N. Lykossov
, and
D. V. Mironov

Abstract

The turbulence closure problem for convective boundary layers is considered with the chief aim to advance the understanding and modeling of nonlocal transport due to large-scale semiorganized structures. The key role here is played by third-order moments (fluxes of fluxes). The problem is treated by the example of the vertical turbulent flux of potential temperature. An overview is given of various schemes ranging from comparatively simple countergradient-transport formulations to sophisticated turbulence closures based on budget equations for the second-order moments. As an alternative to conventional “turbulent diffusion parameterization” for the flux of flux of potential temperature, a “turbulent advection plus diffusion parameterization” is developed and diagnostically tested against data from a large eddy simulation. Employing this parameterization, the budget equation for the potential temperature flux provides a nonlocal turbulence closure formulation for the flux in question. The solution to this equation in terms of the Green function is nothing but an integral turbulence closure. In particular cases it reduces to closure schemes proposed earlier, for example, the Deardorff countergradient correction closure, the Wyngaard and Weil transport-asymmetry closure employing the second derivative of transported scalar, and the Berkowicz and Prahm integral closure for passive scalars. Moreover, the proposed Green-function solution provides a mathematically rigorous procedure for the Wyngaard decomposition of turbulence statistics into the bottom-up and top-down components. The Green-function decomposition exhibits nonlinear vertical profiles of the bottom-up and top-down components of the potential temperature flux in sharp contrast to universally adopted linear profiles. For modeling applications, the proposed closure should be equipped with recommendations as to how to specify the temperature and vertical velocity variances and the vertical velocity skewness.

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D. V. Mironov
,
V. M. Gryanik
,
V. N. Lykossov
, and
S. S. Zilitinkevich

Abstract

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M. Wendisch
,
M. Brückner
,
S. Crewell
,
A. Ehrlich
,
J. Notholt
,
C. Lüpkes
,
A. Macke
,
J. P. Burrows
,
A. Rinke
,
J. Quaas
,
M. Maturilli
,
V. Schemann
,
M. D. Shupe
,
E. F. Akansu
,
C. Barrientos-Velasco
,
K. Bärfuss
,
A.-M. Blechschmidt
,
K. Block
,
I. Bougoudis
,
H. Bozem
,
C. Böckmann
,
A. Bracher
,
H. Bresson
,
L. Bretschneider
,
M. Buschmann
,
D. G. Chechin
,
J. Chylik
,
S. Dahlke
,
H. Deneke
,
K. Dethloff
,
T. Donth
,
W. Dorn
,
R. Dupuy
,
K. Ebell
,
U. Egerer
,
R. Engelmann
,
O. Eppers
,
R. Gerdes
,
R. Gierens
,
I. V. Gorodetskaya
,
M. Gottschalk
,
H. Griesche
,
V. M. Gryanik
,
D. Handorf
,
B. Harm-Altstädter
,
J. Hartmann
,
M. Hartmann
,
B. Heinold
,
A. Herber
,
H. Herrmann
,
G. Heygster
,
I. Höschel
,
Z. Hofmann
,
J. Hölemann
,
A. Hünerbein
,
S. Jafariserajehlou
,
E. Jäkel
,
C. Jacobi
,
M. Janout
,
F. Jansen
,
O. Jourdan
,
Z. Jurányi
,
H. Kalesse-Los
,
T. Kanzow
,
R. Käthner
,
L. L. Kliesch
,
M. Klingebiel
,
E. M. Knudsen
,
T. Kovács
,
W. Körtke
,
D. Krampe
,
J. Kretzschmar
,
D. Kreyling
,
B. Kulla
,
D. Kunkel
,
A. Lampert
,
M. Lauer
,
L. Lelli
,
A. von Lerber
,
O. Linke
,
U. Löhnert
,
M. Lonardi
,
S. N. Losa
,
M. Losch
,
M. Maahn
,
M. Mech
,
L. Mei
,
S. Mertes
,
E. Metzner
,
D. Mewes
,
J. Michaelis
,
G. Mioche
,
M. Moser
,
K. Nakoudi
,
R. Neggers
,
R. Neuber
,
T. Nomokonova
,
J. Oelker
,
I. Papakonstantinou-Presvelou
,
F. Pätzold
,
V. Pefanis
,
C. Pohl
,
M. van Pinxteren
,
A. Radovan
,
M. Rhein
,
M. Rex
,
A. Richter
,
N. Risse
,
C. Ritter
,
P. Rostosky
,
V. V. Rozanov
,
E. Ruiz Donoso
,
P. Saavedra Garfias
,
M. Salzmann
,
J. Schacht
,
M. Schäfer
,
J. Schneider
,
N. Schnierstein
,
P. Seifert
,
S. Seo
,
H. Siebert
,
M. A. Soppa
,
G. Spreen
,
I. S. Stachlewska
,
J. Stapf
,
F. Stratmann
,
I. Tegen
,
C. Viceto
,
C. Voigt
,
M. Vountas
,
A. Walbröl
,
M. Walter
,
B. Wehner
,
H. Wex
,
S. Willmes
,
M. Zanatta
, and
S. Zeppenfeld

Abstract

Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric–ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.

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