Barotropic Impacts of Surface Friction on Eddy Kinetic Energy and Momentum Fluxes: An Alternative to the Barotropic Governor

2012 ◽  
Vol 69 (10) ◽  
pp. 3028-3039 ◽  
Author(s):  
Elizabeth A. Barnes ◽  
Chaim I. Garfinkel
Keyword(s):  
Kinetic Energy ◽  
Momentum Flux ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Friction ◽  
Eddy Kinetic Energy ◽  
Surface Drag ◽  
Momentum Fluxes ◽  
Upper Level ◽  
Energy And Momentum

Abstract As the surface drag is increased in a comprehensive general circulation model (GCM), the upper-level zonal winds decrease and eddy momentum flux convergence into the jet core increases. Globally averaged eddy kinetic energy decreases, a response that is inconsistent with the conventional barotropic governor mechanism whereby decreased barotropic shears encourage baroclinic wave growth. As the conventional barotropic governor appears insufficient to explain the entire response in the comprehensive GCM, the nondivergent barotropic model on the sphere is used to demonstrate an additional mechanism for the effect of surface drag on eddy momentum fluxes and eddy kinetic energy. Analysis of the pseudomomentum budget shows that increased drag modifies the background meridional vorticity gradient, which allows for enhanced eddy momentum flux convergence and decreased eddy kinetic energy in the presence of a constant eddy source. This additional feedback may explain the changes in eddy momentum fluxes observed in the comprehensive GCM and was likely present in previous work on the barotropic governor.

scholarly journals Three-dimensional parameterizations of the synoptic scale kinetic energy and momentum flux in the Earth's atmosphere

2011 ◽  
Vol 18 (6) ◽  
pp. 807-827 ◽  
Author(s):  
D. Coumou ◽  
V. Petoukhov ◽  
A. V. Eliseev
Keyword(s):  
Kinetic Energy ◽  
Momentum Flux ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Storm Tracks ◽  
Synoptic Scale ◽  
Dynamical Equations ◽  
Turbulent Diffusion Coefficient ◽  
Energy And Momentum

Abstract. We present a new set of statistical-dynamical equations (SDEs) which can accurately reproduce the three-dimensional atmospheric fields of synoptic scale kinetic energy and momentum flux. The set of equations is closed by finding proper parameterizations for the vertical macro-turbulent diffusion coefficient and ageostrophic terms. The equations have been implemented in a new SD atmosphere model, named Aeolus. We show that the synoptic scale kinetic energy and momentum fluxes generated by the model are in good agreement with empirical data, which were derived from bandpass-filtered ERA-40 data. In addition to present-day climate, the model is tested for substantially colder (last glacial maximum) and warmer (2×CO2) climates, and shown to be in agreement with general circulation model (GCM) results. With the derived equations, one can efficiently study the position and strength of storm tracks under different climate scenarios with calculation time a fraction of those of GCMs. This work prepares ground for the development of a new generation of fast Earth System Models of Intermediate Complexity which are able to perform multi-millennia simulations in a reasonable time frame while appropriately accounting for the climatic effect of storm tracks.

scholarly journals Energy of Midlatitude Transient Eddies in Idealized Simulations of Changed Climates

2008 ◽  
Vol 21 (22) ◽  
pp. 5797-5806 ◽  
Author(s):  
Paul A. O’Gorman ◽  
Tapio Schneider
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Radiative Forcing ◽  
General Circulation ◽  
Thermal Structure ◽  
Circulation Model ◽  
Static Stability ◽  
Eddy Kinetic Energy ◽  
Available Potential Energy ◽  
Wide Range

Abstract As the climate changes, changes in static stability, meridional temperature gradients, and availability of moisture for latent heat release may exert competing effects on the energy of midlatitude transient eddies. This paper examines how the eddy kinetic energy in midlatitude baroclinic zones responds to changes in radiative forcing in simulations with an idealized moist general circulation model. In a series of simulations in which the optical thickness of the longwave absorber is varied over a wide range, the eddy kinetic energy has a maximum for a climate with mean temperature similar to that of present-day earth, with significantly smaller values both for warmer and for colder climates. In a series of simulations in which the meridional insolation gradient is varied, the eddy kinetic energy increases monotonically with insolation gradient. In both series of simulations, the eddy kinetic energy scales approximately linearly with the dry mean available potential energy averaged over the baroclinic zones. Changes in eddy kinetic energy can therefore be related to the changes in the atmospheric thermal structure that affect the mean available potential energy.

scholarly journals Downstream Self-Destruction of Storm Tracks

2011 ◽  
Vol 68 (10) ◽  
pp. 2459-2464 ◽  
Author(s):  
Yohai Kaspi ◽  
Tapio Schneider
Keyword(s):  
Kinetic Energy ◽  
Rotation Rate ◽  
General Circulation ◽  
Energy Transport ◽  
Circulation Model ◽  
Eddy Kinetic Energy ◽  
Storm Tracks ◽  
Planetary Rotation ◽  
The Pacific ◽  
Longitudinal Length

Abstract The Northern Hemisphere storm tracks have maximum intensity over the Pacific and Atlantic basins; their intensity is reduced over the continents downstream. Here, simulations with an idealized aquaplanet general circulation model are used to demonstrate that even without continents, storm tracks have a self-determined longitudinal length scale. Their length is controlled primarily by the planetary rotation rate and is similar to that of Earth’s storm tracks for Earth’s rotation rate. Downstream, storm tracks self-destruct: the downstream eddy kinetic energy is lower than it would be without the zonal asymmetries that cause localized storm tracks. Likely involved in the downstream self-destruction of storm tracks are the energy fluxes associated with them. The zonal asymmetries that cause localized storm tracks enhance the energy transport through the generation of stationary eddies, and this leads to a reduced baroclinicity that persists far downstream of the eddy kinetic energy maxima.

scholarly journals Structure, Energy, and Parameterization of Inertia–Gravity Waves in Dry and Moist Simulations of a Baroclinic Wave Life Cycle

2014 ◽  
Vol 71 (7) ◽  
pp. 2390-2414 ◽  
Author(s):  
Mohammad Mirzaei ◽  
Christoph Zülicke ◽  
Ali R. Mohebalhojeh ◽  
Farhang Ahmadi-Givi ◽  
Riwal Plougonven
Keyword(s):  
Life Cycle ◽  
Kinetic Energy ◽  
Gravity Wave ◽  
Wave Energy ◽  
General Circulation ◽  
Eddy Kinetic Energy ◽  
Baroclinic Wave ◽  
Starting Point ◽  
Upper Level ◽  
The Impact

Abstract The impact of moisture on inertia–gravity wave generation is assessed for an idealized unstable baroclinic wave using the Weather Research and Forecasting Model (WRF) in a channel on the f plane. The evolution of these waves in a moist simulation is compared with a dry simulation. The centers of action for inertia–gravity wave activity are identified as the equatorward-moving upper-level front and the poleward-progressing upper-level jet–surface front system. Four stratospheric wave packets are found, which are significantly more intense in the moist simulation and have slightly higher frequency. They are characterized by their structure and position during the baroclinic wave life cycle and are related to forcing terms in jet, front, and convection systems. By exploring the time series of mass and energy, it is shown that the release of latent heat leads to a change in enthalpy, an increase in the eddy kinetic energy, and an intensification of the inertia–gravity wave energy. The ratio of the inertia–gravity wave energy to the eddy kinetic energy is estimated to be about 1/200 for the moist simulation, which is 3 times larger than that for the dry simulation. An empirical parameterization scheme for the inertia–gravity wave energy is proposed, based on the fast large-scale ageostrophic flow associated with the jet, front, and convection. The diagnosed stratospheric inertia–gravity wave energy is well captured by this parameterization in six WRF simulations with different moisture and resolutions. The approach used to construct the parameterization may serve as a starting point for state-dependent nonorographic gravity wave drag schemes in general circulation models.

scholarly journals Equilibration of a Baroclinic Planetary Atmosphere toward the Limit of Vanishing Bottom Friction

2016 ◽  
Vol 73 (8) ◽  
pp. 3249-3272 ◽  
Author(s):  
Junyi Chai ◽  
Malte Jansen ◽  
Geoffrey K. Vallis
Keyword(s):  
Kinetic Energy ◽  
Time Scale ◽  
General Circulation ◽  
Lower Boundary ◽  
Circulation Model ◽  
Bottom Friction ◽  
Lower Atmosphere ◽  
Westerly Jet ◽  
Momentum Fluxes ◽  
Westerly Jets

Abstract This paper discusses whether and how a baroclinic atmosphere can equilibrate with very small bottom friction in a dry primitive equation general circulation model. The model is forced by a Newtonian relaxation of temperature to a prescribed temperature profile, and it is damped by a linear friction near the lower boundary. When friction is decreased by four orders of magnitude, kinetic energy dissipation by friction gradually becomes negligible, while “energy recycling” becomes dominant. In this limit kinetic energy is converted back into potential energy at the largest scales, thus closing the energy cycle without significant frictional dissipation. The momentum fluxes are of opposite sign in the upper and lower atmosphere: in the upper atmosphere, eddies converge momentum into the westerly jets; however, in the lower atmosphere, the eddies diverge momentum out of the westerly jets. The secondary circulation driven by the meridional eddy momentum fluxes thus acts to increase the baroclinicity of the westerly jet. This regime may be relevant for the Jovian atmosphere, where the frictional time scale may be much larger than the radiative damping time scale.

scholarly journals Seasonal variability of subthermocline eddy kinetic energy east of the Philippines

2020 ◽  
Author(s):  
Linlin Zhang ◽  
Yuchao Hui ◽  
Tangdong Qu ◽  
Dunxin Hu
Keyword(s):  
Kinetic Energy ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
The Philippines ◽  
Early Spring ◽  
Eddy Kinetic Energy ◽  
Barotropic Instability ◽  
Equatorial Undercurrent ◽  
Halmahera Eddy

AbstractSeasonal modulation of subthermocline Eddy Kinetic Energy (EKE) east of the Philippines and its associated dynamics are studied, using mooring measurements and outputs from an eddy-resolving ocean general circulation model for the period from 2000 to 2017. Significantly high EKE appears below the thermocline in the latitude band between 5°N and 14°N east of the Philippines. Separated by 10°N, the EKE in the northern and southern parts of the region shows nearly opposite seasonal cycles, with its magnitude reaching maximum in early spring and minimum in summer in the northern part and reaching maximum in summer and minimum in winter in the southern part of the region. Further investigation indicates that both baroclinic and barotropic instabilities are essential in generating the subthermocline eddies, but the seasonal variation of subthermocline EKE is mainly caused by the seasonal modulation of barotropic instability. The seasonal modulation of barotropic instability in the northern and southern part of the region is associated with the seasonal evolution of North Equatorial Undercurrent and Halmahera Eddy, respectively.

Sensitivity of the Latitude of the Surface Westerlies to Surface Friction

2007 ◽  
Vol 64 (8) ◽  
pp. 2899-2915 ◽  
Author(s):  
Gang Chen ◽  
Isaac M. Held ◽  
Walter A. Robinson
Keyword(s):  
Kinetic Energy ◽  
Momentum Flux ◽  
Phase Speed ◽  
Surface Friction ◽  
Water Model ◽  
Shallow Water Model ◽  
Mean Flow ◽  
Zonal Winds ◽  
Adjustment Time ◽  
Critical Latitude

The sensitivity to surface friction of the latitude of the surface westerlies and the associated eddy-driven midlatitude jet is studied in an idealized dry GCM. The westerlies move poleward as the friction is reduced in strength. An increase in the eastward phase speed of midlatitude eddies is implicated as playing a central role in this shift. This shift in latitude is mainly determined by changes in the friction on the zonal mean flow rather than the friction on the eddies. If the friction on the zonal mean is reduced instantaneously, the response reveals two distinctive adjustment time scales. In the fast adjustment over the first 10–20 days, there is an increase in the barotropic component of zonal winds and a substantial decrease in the eddy kinetic energy; the shift in the surface westerlies and jet latitude occurs in a slower adjustment. The space–time eddy momentum flux spectra suggest that the key to the shift is a poleward movement in the subtropical critical latitude associated with the faster eastward phase speeds in the dominant midlatitude eddies. The view is supported by simulating the upper-tropospheric dynamics in a stochastically stirred nonlinear shallow water model.

The Response of an Idealized Atmosphere to Localized Tropical Heating: Superrotation and the Breakdown of Linear Theory

2018 ◽  
Vol 75 (1) ◽  
pp. 3-20 ◽  
Author(s):  
Nicholas J. Lutsko
Keyword(s):  
Temperature Gradient ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Heating Rates ◽  
Momentum Fluxes ◽  
The Mean ◽  
The Stability ◽  
The Waves ◽  
Large Heating

An equatorial heat source mimicking the strong diabatic heating above the west Pacific is added to an idealized, dry general circulation model. For small (<0.5 K day−1) heating rates the responses closely match the expectations from linear Matsuno–Gill theory, though the amplitudes of the responses increase sublinearly. This “linear” regime breaks down for larger heating rates and it is found that this is because the stability of the tropical atmosphere increases. At the same time, the equatorial winds increasingly superrotate. This superrotation is driven by stationary eddy momentum fluxes by the waves excited by the heating and is damped by the vertical advection of low-momentum air by the mean flow and, at large heating rates, by the divergence of momentum by transient eddies. These dynamics are explored in additional experiments in which the equator-to-pole temperature gradient is varied. Very strong superrotation is produced when a large heating rate is applied to a setup with a relatively weak equator-to-pole temperature gradient, though there is no evidence that this is a case of “runaway” superrotation.

scholarly journals Vertical resolution dependence of gravity wave momentum flux simulated by an atmospheric general circulation model

2014 ◽  
Vol 7 (6) ◽  
pp. 7559-7573
Author(s):  
S. Watanabe ◽  
K. Sato ◽  
Y. Kawatani ◽  
M. Takahashi
Keyword(s):  
Gravity Wave ◽  
Momentum Flux ◽  
General Circulation ◽  
Circulation Model ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Vertical Resolution ◽  
Time Step ◽  
Atmospheric General Circulation ◽  
Wave Momentum

Abstract. The dependence of the gravity wave spectra of energy and momentum flux on the horizontal resolution and time step of atmospheric general circulation models (AGCMs) has been thoroughly investigated in the past. In contrast, much less attention has been given to the dependence of these gravity wave parameters on models' vertical resolutions. The present study demonstrates the dependence of gravity wave momentum flux in the stratosphere and mesosphere on the model's vertical resolution, which is evaluated using an AGCM with a horizontal resolution of about 0.56°. We performed a series of sensitivity test simulations changing only the model's vertical resolution above a height of 8 km, and found that inertial gravity waves with short vertical wavelengths simulated at higher vertical resolutions likely play an important role in determining the gravity wave momentum flux in the stratosphere and mesosphere.

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