scholarly journals First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N

2015 ◽  
Vol 33 (9) ◽  
pp. 1091-1096 ◽  
Author(s):  
M. Placke ◽  
P. Hoffmann ◽  
M. Rapp
Keyword(s):  
Doppler Radar ◽  
Middle Atmosphere ◽  
Meridional Wind ◽  
Momentum Balance ◽  
Additional Contribution ◽  
Mean Flow ◽  
Annual Cycles ◽  
Coriolis Acceleration ◽  
The Mean ◽  
Zonal Momentum Balance

Abstract. Gravity waves (GWs) greatly influence the background state of the middle atmosphere by imposing their momentum on the mean flow upon breaking and by thus driving, e.g., the upper mesospheric summer zonal wind reversal. In this situation momentum is conserved by a balance between the vertical divergence of GW momentum flux (the so-called GW drag) and the Coriolis acceleration of the mean meridional wind. In this study, we present first quantitative mean annual cycles of these two balancing quantities from the medium frequency Doppler radar at the polar site Saura (SMF radar, 69° N, 16° E). Three-year means for 2009 through 2011 clearly show that the observed zonal momentum balance between 70 and 100 km with contributions from GWs only is fulfilled during summer when GW activity is strongest and more stable than in winter. During winter, the balance between GW drag and Coriolis acceleration of the mean meridional wind is not existent, which is likely due to the additional contribution from planetary waves, which are not considered by the present investigation. The differences in the momentum balance between summer and winter conditions are additionally clarified by 3-month mean vertical profiles for summer 2010 and winter 2010/2011.

scholarly journals On the Evaluation of Seasonal Variability of the Ocean Kinetic Energy

2017 ◽  
Vol 47 (7) ◽  
pp. 1675-1683 ◽  
Author(s):  
Dujuan Kang ◽  
Enrique N. Curchitser
Keyword(s):  
Kinetic Energy ◽  
Seasonal Variability ◽  
Moving Average ◽  
Spatial Inhomogeneity ◽  
Mean Flow ◽  
Annual Cycles ◽  
Residual Term ◽  
The Mean ◽  
Mean Differences ◽  
Average Filter

AbstractThe seasonal cycles of the mean kinetic energy (MKE) and eddy kinetic energy (EKE) are compared in an idealized flow as well as in a realistic simulation of the Gulf Stream (GS) region based on three commonly used definitions: orthogonal, nonorthogonal, and moving-average filtered decompositions of the kinetic energy (KE). It is shown that only the orthogonal KE decomposition can define the physically consistent MKE and EKE that precisely represents the KEs of the mean flow and eddies, respectively. The nonorthogonal KE decomposition gives rise to a residual term that contributes to the seasonal variability of the eddies, and therefore the obtained EKE is not precisely defined. The residual term is shown to exhibit more significant seasonal variability than EKE in both idealized and realistic GS flows. Neglecting its influence leads to an inaccurate evaluation of the seasonal variability of both the eddies and the total flow. The decomposition using a moving-average filter also results in a nonnegligible residual term in both idealized and realistic GS flows. This type of definition does not ensure conservation of the total KE, even if taking into account the residual term. Moreover, it is shown that the annual cycles of the three types of EKEs or MKEs have different phases and amplitudes. The local differences of the EKE cycles are very prominent in the GS off-coast domain; however, because of the spatial inhomogeneity, the area-mean differences may not be significant.

Application of the IDEMIX Concept for Internal Gravity Waves in the Atmosphere

2020 ◽  
Vol 77 (10) ◽  
pp. 3601-3618
Author(s):  
B. Quinn ◽  
C. Eden ◽  
D. Olbers
Keyword(s):  
Energy Balance ◽  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
The Mean

AbstractThe model Internal Wave Dissipation, Energy and Mixing (IDEMIX) presents a novel way of parameterizing internal gravity waves in the atmosphere. IDEMIX is based on the spectral energy balance of the wave field and has previously been successfully developed as a model for diapycnal diffusivity, induced by internal gravity wave breaking in oceans. Applied here for the first time to atmospheric gravity waves, integration of the energy balance equation for a continuous wave field of a given spectrum, results in prognostic equations for the energy density of eastward and westward gravity waves. It includes their interaction with the mean flow, allowing for an evolving and local description of momentum flux and gravity wave drag. A saturation mechanism maintains the wave field within convective stability limits, and a closure for critical-layer effects controls how much wave flux propagates from the troposphere into the middle atmosphere. Offline comparisons to a traditional parameterization reveal increases in the wave momentum flux in the middle atmosphere due to the mean-flow interaction, resulting in a greater gravity wave drag at lower altitudes. Preliminary validation against observational data show good agreement with momentum fluxes.

scholarly journals Is the Coefficient of Eddy Potential Vorticity Diffusion Positive? Part I: Barotropic Zonal Channel

2018 ◽  
Vol 48 (7) ◽  
pp. 1589-1607 ◽  
Author(s):  
V. O. Ivchenko ◽  
V. B. Zalesny ◽  
B. Sinha
Keyword(s):  
Potential Vorticity ◽  
Independent Solution ◽  
Zonal Flow ◽  
Momentum Balance ◽  
Eddy Fluxes ◽  
The Mean ◽  
Zonal Momentum Balance ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Zonal Momentum

AbstractThe question of whether the coefficient of diffusivity of potential vorticity by mesoscale eddies is positive is studied for a zonally reentrant barotropic channel using the quasigeostrophic approach. The topography is limited to the first mode in the meridional direction but is unlimited in the zonal direction. We derive an analytic solution for the stationary (time independent) solution. New terms associated with parameterized eddy fluxes of potential vorticity appear both in the equations for the mean zonal momentum balance and in the kinetic energy balance. These terms are linked with the topographic form stress exerted by parameterized eddies. It is demonstrated that in regimes with zonal flow (analogous to the Antarctic Circumpolar Current), the coefficient of eddy potential vorticity diffusivity must be positive.

scholarly journals Zonal Momentum Balance, Potential Vorticity Dynamics, and Mass Fluxes on Near-Surface Isentropes

2005 ◽  
Vol 62 (6) ◽  
pp. 1884-1900 ◽  
Author(s):  
Tapio Schneider
Keyword(s):  
Potential Vorticity ◽  
Momentum Balance ◽  
Near Surface ◽  
Global Circulation ◽  
Balance Condition ◽  
Mass Fluxes ◽  
Vorticity Dynamics ◽  
The Mean ◽  
Zonal Momentum Balance ◽  
Zonal Momentum

Abstract While it has been recognized for some time that isentropic coordinates provide a convenient framework for theories of the global circulation of the atmosphere, the role of boundary effects in the zonal momentum balance and in potential vorticity dynamics on isentropes that intersect the surface has remained unclear. Here, a balance equation is derived that describes the temporal and zonal mean balance of zonal momentum and of potential vorticity on isentropes, including the near-surface isentropes that sometimes intersect the surface. Integrated vertically, the mean zonal momentum or potential vorticity balance leads to a balance condition that relates the mean meridional mass flux along isentropes to eddy fluxes of potential vorticity and surface potential temperature. The isentropic-coordinate balance condition formally resembles balance conditions well known in quasigeostrophic theory, but on near-surface isentropes it generally differs from the quasigeostrophic balance conditions. Not taking the intersection of isentropes with the surface into account, quasigeostrophic theory does not adequately represent the potential vorticity dynamics and mass fluxes on near-surface isentropes—a shortcoming that calls into question the relevance of quasigeostrophic theories for the macroturbulence and global circulation of the atmosphere.

scholarly journals EFFECTS OF ACTUATOR IMPACT ON THE NONLINEAR DYNAMICS OF A VALVELESS PUMPING SYSTEM

2011 ◽  
Vol 11 (03) ◽  
pp. 591-624 ◽  
Author(s):  
TIAN-SHIANG YANG ◽  
CHI-CHUNG WANG
Keyword(s):  
Fluid Transport ◽  
Numerical Solutions ◽  
Lumped Parameter Model ◽  
Momentum Balance ◽  
Parameter Study ◽  
Driving Frequency ◽  
Mean Flow ◽  
Valveless Pumping ◽  
The Mean ◽  
The Impact

Valveless pumping assists in fluid transport in various biomedical and engineering systems. Here we focus on one factor that has often been overlooked in previous studies of valveless pumping, namely the impact that a compression actuator exerts upon the pliant part of the system when they collide. In particular, a fluid-filled closed-loop system is considered, which consists of two distensible reservoirs connected by two rigid tubes, with one of the reservoirs compressed by an actuator at a prescribed frequency. A lumped-parameter model with constant coefficients accounting for mass and momentum balance in the system is constructed. Based on such a model, a mean flow in the fluid loop can only be produced by system asymmetry and the nonlinear effects associated with actuator impact. Through asymptotic and numerical solutions of the model, a systematic parameter study is carried out, thereby revealing the rich and complex system dynamics that strongly depends upon the driving frequency of the actuator and other geometrical and material properties of the system. The driving frequency dependence of the mean flowrate in the fluid loop and that of the mean reservoir pressures also are examined for a number of representative cases.

Numerical study of turbulent magnetohydrodynamic channel flow

2007 ◽  
Vol 572 ◽  
pp. 179-188 ◽  
Author(s):  
THOMAS BOECK ◽  
DMITRY KRASNOV ◽  
EGBERT ZIENICKE
Keyword(s):  
Channel Flow ◽  
Numerical Study ◽  
Layer Structure ◽  
Momentum Balance ◽  
Mean Flow ◽  
Mean Velocity ◽  
Static Approximation ◽  
The Mean ◽  
Magnetohydrodynamic Channel ◽  
Normal Magnetic Field

Mean flow properties of turbulent magnetohydrodynamic channel flow with electrically insulating channel walls are studied using high-resolution direct numerical simulations. The Lorentz force due to the homogeneous wall-normal magnetic field is computed in the quasi-static approximation. For strong magnetic fields, the mean velocity profile shows a clear three-layer structure consisting of a viscous region near each wall and a plateau in the middle connected by logarithmic layers. This structure reflects the significance of viscous, turbulent, and electromagnetic stresses in the streamwise momentum balance dominating the viscous, logarithmic, and plateau regions, respectively. The width of the logarithmic layers changes with the ratio of Reynolds- and Hartmann numbers. Turbulent stresses typically decay more rapidly away from the walls than predicted by mixing-length models.

Wave propagation and transport in the middle atmosphere

1980 ◽  
Vol 296 (1418) ◽  
pp. 73-85 ◽  
Keyword(s):  
Wave Propagation ◽  
Middle Atmosphere ◽  
Transport Processes ◽  
Planetary Waves ◽  
Wave Radiation ◽  
Mean Flow ◽  
Flow Interaction ◽  
Wave Transport ◽  
Equatorial Wave ◽  
The Mean

The dynamics of wave propagation and wave transport are reviewed for vertically propagating, forced, planetary scale waves in the middle atmosphere. Such waves can be divided into two major classes: extratropical planetary waves and equatorial waves. The most important waves of the former class are quasi-stationary Rossby modes of zonal wave numbers 1 and 2 (1 or 2 waves around a latitude circle), which propagate vertically only during the w inter season when the m ean winds are westerly. These modes transport heat and ozone towards the poles, thus maintaining the mean temperature above its radiative equilibrium value in high latitudes and producing the high latitude ozone maximum . It is shown that these wave transport processes depend on wave transience and wave dam ping. The precise form of this dependency is illustrated for transport of a strongly stratified tracer by small amplitude planetary waves. The observed equatorial wave modes are of two types: an eastward propagating Kelvin m ode and a westward propagating mixed Rossby—gravity mode. These modes are therm ally damped in the stratosphere where they interact with the mean flow to produce eastward and westward accelerations, respectively. It is shown tha t in the absence of mechanical dissipation this wave—mean flow interaction is caused by the vertical divergence of a wave ‘radiation stress’. This wave—mean flow interaction process is responsible for producing the well known equatorial quasi-biennial oscillation.

A physical model of the turbulent boundary layer consonant with mean momentum balance structure

2007 ◽  
Vol 365 (1852) ◽  
pp. 823-840 ◽  
Author(s):  
Joe Klewicki ◽  
Paul Fife ◽  
Tie Wei ◽  
Pat McMurtry
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Physical Model ◽  
Momentum Equation ◽  
Momentum Balance ◽  
Dynamical Structure ◽  
Mean Flow ◽  
Structure And Dynamics ◽  
The Mean ◽  
Balance Structure

Recent studies by the present authors have empirically and analytically explored the properties and scaling behaviours of the Reynolds averaged momentum equation as applied to wall-bounded flows. The results from these efforts have yielded new perspectives regarding mean flow structure and dynamics, and thus provide a context for describing flow physics. A physical model of the turbulent boundary layer is constructed such that it is consonant with the dynamical structure of the mean momentum balance, while embracing independent experimental results relating, for example, to the statistical properties of the vorticity field and the coherent motions known to exist. For comparison, the prevalent, well-established, physical model of the boundary layer is briefly reviewed. The differences and similarities between the present and the established models are clarified and their implications discussed.

scholarly journals Eastward-propagating planetary waves in the polar middle atmosphere

2021 ◽  
Vol 21 (23) ◽  
pp. 17495-17512
Author(s):  
Liang Tang ◽  
Sheng-Yang Gu ◽  
Xian-Kang Dou
Keyword(s):  
Middle Atmosphere ◽  
Flow Instability ◽  
Planetary Waves ◽  
Background Wind ◽  
Mean Flow ◽  
Zonal Wavenumber ◽  
Critical Layers ◽  
The Mean ◽  
Modern Era ◽  
Research Analysis

Abstract. According to Modern-Era Retrospective Research Analysis for Research and Applications (MERRA-2) temperature and wind datasets in 2019, this study presents the global variations in the eastward-propagating wavenumber 1 (E1), 2 (E2), 3 (E3) and 4 (E4) planetary waves (PWs) and their diagnostic results in the polar middle atmosphere. We clearly demonstrate the eastward wave modes exist during winter periods with westward background wind in both hemispheres. The maximum wave amplitudes in the Southern Hemisphere (SH) are slightly larger and lie lower than those in the Northern Hemisphere (NH). Moreover, the wave perturbations peak at lower latitudes with smaller amplitudes as the wavenumber increases. The period of the E1 mode varies between 3–5 d in both hemispheres, while the period of the E2 mode is slightly longer in the NH (∼ 48 h) than in the SH (∼ 40 h). The periods of the E3 are ∼ 30 h in both the SH and the NH, and the period of E4 is ∼ 24 h. Despite the shortening of wave periods with the increase in wavenumber, their mean phase speeds are relatively stable, ∼ 53, ∼ 58, ∼ 55 and ∼ 52 m/s at 70∘ latitudes for E1, E2, E3 and E4, respectively. The eastward PWs occur earlier with increasing zonal wavenumber, which agrees well with the seasonal variations in the critical layers generated by the background wind. Our diagnostic analysis also indicates that the mean flow instability in the upper stratosphere and upper mesosphere might contribute to the amplification of the eastward PWs.

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