Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings

2021 ◽  
Author(s):  
Masaru Yamamoto ◽  
Takumi Hirose ◽  
Kohei Ikeda ◽  
Masaaki Takahashi
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Circulation Model ◽  
Stationary Wave ◽  
Static Stability ◽  
Small Scale ◽  
Mean Flow ◽  
Short Period ◽  
Low Latitudes ◽  
Thermal Tides

<p>General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/s<sup></sup>with rates of 0.2–0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.</p>

scholarly journals Generation of gravity waves from thermal tides in the Venus atmosphere

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Norihiko Sugimoto ◽  
Yukiko Fujisawa ◽  
Hiroki Kashimura ◽  
Katsuyuki Noguchi ◽  
Takeshi Kuroda ◽  
...  
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Cloud Layer ◽  
Dimensional Structure ◽  
Wave Radiation ◽  
Small Scale ◽  
Thermal Tides ◽  
Venus Atmosphere

AbstractGravity waves play essential roles in the terrestrial atmosphere because they propagate far from source regions and transport momentum and energy globally. Gravity waves are also observed in the Venus atmosphere, but their characteristics have been poorly understood. Here we demonstrate activities of small-scale gravity waves using a high-resolution Venus general circulation model with less than 20 and 0.25 km in the horizontal and vertical grid intervals, respectively. We find spontaneous gravity wave radiation from nearly balanced flows. In the upper cloud layer (~70 km), the thermal tides in the super-rotation are primary sources of small-scale gravity waves in the low-latitudes. Baroclinic/barotropic waves are also essential sources in the mid- and high-latitudes. The small-scale gravity waves affect the three-dimensional structure of the super-rotation and contribute to material mixing through their breaking processes. They propagate vertically and transport momentum globally, which decelerates the super-rotation in the upper cloud layer (~70 km) and accelerates it above ~80 km.

scholarly journals A New Method to Estimate Three-Dimensional Residual-Mean Circulation in the Middle Atmosphere and Its Application to Gravity Wave–Resolving General Circulation Model Data

2013 ◽  
Vol 70 (12) ◽  
pp. 3756-3779 ◽  
Author(s):  
Kaoru Sato ◽  
Takenari Kinoshita ◽  
Kota Okamoto
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Mean Flow ◽  
Flux Divergence ◽  
Mean Circulation ◽  
Residual Mean Circulation ◽  
Wave Induced

Abstract A new method is proposed to estimate three-dimensional (3D) material circulation driven by waves based on recently derived formulas by Kinoshita and Sato that are applicable to both Rossby waves and gravity waves. The residual-mean flow is divided into three, that is, balanced flow, unbalanced flow, and Stokes drift. The latter two are wave-induced components estimated from momentum flux divergence and heat flux divergence, respectively. The unbalanced mean flow is equivalent to the zonal-mean flow in the two-dimensional (2D) transformed Eulerian mean (TEM) system. Although these formulas were derived using the “time mean,” the underlying assumption is the separation of spatial or temporal scales between the mean and wave fields. Thus, the formulas can be used for both transient and stationary waves. Considering that the average is inherently needed to remove an oscillatory component of unaveraged quadratic functions, the 3D wave activity flux and wave-induced residual-mean flow are estimated by an extended Hilbert transform. In this case, the scale of mean flow corresponds to the whole scale of the wave packet. Using simulation data from a gravity wave–resolving general circulation model, the 3D structure of the residual-mean circulation in the stratosphere and mesosphere is examined for January and July. The zonal-mean field of the estimated 3D circulation is consistent with the 2D circulation in the TEM system. An important result is that the residual-mean circulation is not zonally uniform in both the stratosphere and mesosphere. This is likely caused by longitudinally dependent wave sources and propagation characteristics. The contribution of planetary waves and gravity waves to these residual-mean flows is discussed.

Dynamical effect on the Venusian thermal structure simulated by a general circulation model

2021 ◽  
Author(s):  
Hiroki Ando ◽  
Kotaro Takaya ◽  
Masahiro Takagi ◽  
Norihiko Sugimoto ◽  
Takeshi Imamura ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Polar Region ◽  
Thermal Structure ◽  
Circulation Model ◽  
Static Stability ◽  
Type Wave ◽  
Low Latitudes ◽  
Mean Meridional Circulation ◽  
The Mean

<div class="page" title="Page 2"> <div class="layoutArea"> <div class="column"> <p>Distributions of temperature and static stability in the Venus atmosphere consistent with recent radio occultation measurements are reproduced using a general circulation model. A low-stability layer is maintained at low- and mid-latitudes at 50–60 km altitude and is sandwiched by high- and moderate-stability layers extending above 60 and below 50  km, respectively. In the polar region, the low-stability layer is located at 46–63 km altitude and the relatively low-stability layer is also found at 40–46 km altitude. To investigate how these thermal structures form, we examine the dynamical effects of the atmospheric motions on the static stability below 65 km altitude. The results show that the heat transport due to the mean meridional circulation is important at low-latitudes. At mid- and high-latitudes, meanwhile, the baroclinic Rossby-type wave plays an important role in maintaining the thermal structure. In addition, appreciable equatorward heat transport is found to maintain the deep and low-stability layer in the polar region, which might be induced by the interaction between the baroclinic Rossby-type wave in the low-stability layer and the trapped Rossby-type wave below it.</p> </div> </div> </div>

scholarly journals Global Distribution of Gravity Wave Sources and Fields in the Martian Atmosphere during Equinox and Solstice Inferred from a High-Resolution General Circulation Model

2016 ◽  
Vol 73 (12) ◽  
pp. 4895-4909 ◽  
Author(s):  
Takeshi Kuroda ◽  
Alexander S. Medvedev ◽  
Erdal Yiğit ◽  
Paul Hartogh
Keyword(s):  
High Resolution ◽  
General Circulation Model ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
The Body ◽  
Small Scale ◽  
Vertical Fluxes ◽  
Low Latitudes ◽  
Horizontal Grid

Abstract Results of simulations with a new high-resolution Martian general circulation model (MGCM) (T106 spectral resolution, or ~67-km horizontal grid size) have been analyzed to reveal global distributions of gravity waves (GWs) during the solstice and equinox periods. They show that shorter-scale harmonics progressively dominate with height, and the body force per unit mass (drag) they impose on the larger-scale flow increases. Mean magnitudes of the drag in the middle atmosphere are tens of meters per second per sol, while instantaneously they can reach thousands of meters per second per sol. Inclusion of small-scale GW harmonics results in an attenuation of the wind jets in the middle atmosphere and in the tendency of their reversal. GW energy in the troposphere due to the shortest-scale harmonics is concentrated in the low latitudes for both seasons and is in a good agreement with observations. The vertical fluxes of wave horizontal momentum are directed mainly against the larger-scale wind. Orographically generated GWs contribute significantly to the total energy of small-scale disturbances and to the drag created by the latter. These waves strongly decay with height, and thus the nonorographic GWs of tropospheric origin dominate near the mesopause. The results of this study can be used to better constrain and validate GW parameterizations in MGCMs.

Sensitivity of the middle and upper atmospheric dynamics to the modification of the gravity wave drag parameterization in ICON model

2021 ◽  
Author(s):  
Khalil Karami ◽  
Sebastian Borchert ◽  
Roland Eichinger ◽  
Christoph Jacobi ◽  
Ales Kuchar ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Southern Oscillation ◽  
Weather Prediction ◽  
Polar Vortex ◽  
Circulation Model ◽  
Internal Variability ◽  
Wave Drag ◽  
Mean Flow

<p>The gravity waves play a crucial role in driving and shaping the middle atmospheric circulation. The Upper-Atmospheric extension of the ICOsahedral Non-hydrostatic (UA-ICON) general circulation model was recently developed with satisfying performances in both idealized test cases and climate simulations, however the sensitivity of the circulation to the parameterized orographic and non-orographic gravity wave drag remains largely unexplored. Using UA-ICON and ICON-NWP, the sensitivity of the dynamics and circulation to both orographic and non-orographic parameterized gravity waves effects are investigated. ICON-NWP stands for the numerical-weather prediction mode of the ICON model (see Zängl et al, 2015, QJRMetSoc), with a model top at about 80 km altitude. The UA-ICON mode differs from ICON-NWP in deep-atmosphere dynamics (instead of shallow-atmosphere dynamics) and upper-atmosphere physics parameterizations being switched on. In addition, the model top is at about 150 km.</p> <p>The sensitivity experiments involve employing repeated annual cycle sea surface temperatures, sea ice, and greenhouse gases under year 1988. This year is selected as both El-Nino southern oscillation and pacific decadal oscillation are in their neutral phase and no explosive volcano eruption has occurred and hence conditions in this year can serve as a useful proxy for the multi-year mean condition and an estimate of its internal variability. For both UA-ICON and ICON-NWP, we perform simulations where in the control (CTL) simulation both orographic and non-orographic gravity wave drags are switched on. The other two experiments are identical to the control simulation except that either orographic (OGWD-off) or b) non-orographic (NGWD-off) gravity wave drags are switched off. The analysis include comparisons between CTL and OGWD-off and NGWD-off simulations and include wave-mean flow interaction diagnostics (Eliassen-Palm flux and its divergence and refractive index of Rossby waves) and mass stream function of the Brewer-Dobson circulation. We also investigate the sudden stratospheric warming frequency and polar vortex morphology in order to understand whether a missing gravity wave forcing can further amplify or curtail the effects of future climate. We present our goal, method as well as first results and discuss possible further analysis. </p>

scholarly journals Mean-Flow Effects of Thermal Tides in the Mesosphere and Lower Thermosphere

2017 ◽  
Vol 74 (6) ◽  
pp. 2043-2063 ◽  
Author(s):  
Erich Becker
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Energy Deposition ◽  
Heat Budget ◽  
Frictional Heating ◽  
Lower Thermosphere ◽  
Mean Flow ◽  
Model Response ◽  
Mesosphere And Lower Thermosphere ◽  
Thermal Tides

Abstract This study addresses the heat budget of the mesosphere and lower thermosphere with regard to the energy deposition of upward-propagating waves. To this end, the energetics of gravity waves are recapitulated using an anelastic version of the primitive equations. This leads to an expression for the energy deposition of waves that is usually resolved in general circulation models. The energy deposition is shown to be mainly due to the frictional heating and, additionally, due to the negative buoyancy production of wave kinetic energy. The frictional heating includes contributions from horizontal and vertical momentum diffusion, as well as from ion drag. This formalism is applied to analyze results from a mechanistic middle-atmosphere general circulation model that includes energetically consistent parameterizations of diffusion, gravity waves, and ion drag. This paper estimates 1) the wave driving and energy deposition of thermal tides, 2) the model response to the excitation of thermal tides, and 3) the model response to the combined energy deposition by parameterized gravity waves and resolved waves. It is found that thermal tides give rise to a significant energy deposition in the lower thermosphere. The temperature response to thermal tides is positive. It maximizes at polar latitudes in the lower thermosphere as a result of poleward circulation branches that are driven by the predominantly westward Eliassen–Palm flux divergence of the tides. In addition, thermal tides give rise to a downward shift and reduction of the gravity wave drag in the upper mesosphere. Including the energy deposition in the model causes a substantial warming in the upper mesosphere and lower thermosphere.

Testing the Limits and Breakdown of the Nonacceleration Theorem for Orographic Stationary Waves

2020 ◽  
Vol 77 (5) ◽  
pp. 1513-1529
Author(s):  
Nicholas J. Lutsko
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Surface Wind ◽  
Circulation Model ◽  
Wave Model ◽  
Stationary Wave ◽  
Surface Wind Speed ◽  
Maximum Height ◽  
Stationary Waves ◽  
Mean Flow

Abstract The nonacceleration theorem states that the torque exerted on the atmosphere by orography is exactly balanced by the convergence of momentum by the stationary waves that the orography excites. This balance is tested in simulations with a stationary wave model and with a dry, idealized general circulation model (GCM), in which large-scale orography is placed at the latitude of maximum surface wind speed. For the smallest mountain considered (maximum height H = 0.5 m), the nonacceleration balance is nearly met, but the damping in the stationary wave model induces an offset between the stationary eddy momentum flux (EMF) convergence and the mountain torque, leading to residual mean flow changes. A stationary nonlinearity appears for larger mountains (H ≥ 10 m), driven by preferential deflection of the flow around the poleward flank of the orography, and causes further breakdown of the nonacceleration balance. The nonlinearity grows as H is increased, and is stronger in the GCM than in the stationary wave model, likely due to interactions with transient eddies. The midlatitude jet shifts poleward for H ≤ 2 km and equatorward for larger mountains, reflecting changes in the transient EMFs, which push the jet poleward for smaller mountains and equatorward for larger mountains. The stationary EMFs consistently force the jet poleward. These results add to our understanding of how orography affects the atmosphere’s momentum budget, providing insight into how the nonacceleration theorem breaks down; the roles of stationary nonlinearities and transients; and how orography affects the strength and latitude of eddy-driven jets.

scholarly journals A Geometric Interpretation of Southern Ocean Eddy Form Stress

2019 ◽  
Vol 49 (10) ◽  
pp. 2553-2570 ◽  
Author(s):  
Mads B. Poulsen ◽  
Markus Jochum ◽  
James R. Maddison ◽  
David P. Marshall ◽  
Roman Nuterman
Keyword(s):  
Southern Ocean ◽  
General Circulation ◽  
Vertical Structure ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Geometric Interpretation ◽  
Mean Flow ◽  
Geometric Framework ◽  
The Mean ◽  
Circumpolar Current

AbstractAn interpretation of eddy form stress via the geometry described by the Eliassen–Palm flux tensor is explored. Complimentary to previous works on eddy Reynolds stress geometry, this study shows that eddy form stress is fully described by a vertical ellipse, whose size, shape, and orientation with respect to the mean flow shear determine the strength and direction of vertical momentum transfers. Following a recent proposal, this geometric framework is here used to form a Gent–McWilliams eddy transfer coefficient that depends on eddy energy and a nondimensional geometric parameter α, bounded in magnitude by unity. The parameter α expresses the efficiency by which eddies exchange energy with baroclinic mean flow via along-gradient eddy buoyancy flux—a flux equivalent to eddy form stress along mean buoyancy contours. An eddy-resolving ocean general circulation model is used to estimate the spatial structure of α in the Southern Ocean and assess its potential to form a basis for parameterization. The eddy efficiency α averages to a low but positive value of 0.043 within the Antarctic Circumpolar Current, consistent with an inefficient eddy field extracting energy from the mean flow. It is found that the low eddy efficiency is mainly the result of that eddy buoyancy fluxes are weakly anisotropic on average. The eddy efficiency is subject to pronounced vertical structure and is maximum at ~3-km depth, where eddy buoyancy fluxes tend to be directed most downgradient. Since α partly sets the eddy form stress in the Southern Ocean, a parameterization for α must reproduce its vertical structure to provide a faithful representation of vertical stress divergence and eddy forcing.

The Dynamical Response to Snow Cover Perturbations in a Large Ensemble of Atmospheric GCM Integrations

2009 ◽  
Vol 22 (5) ◽  
pp. 1208-1222 ◽  
Author(s):  
Christopher G. Fletcher ◽  
Steven C. Hardiman ◽  
Paul J. Kushner ◽  
Judah Cohen
Keyword(s):  
Snow Cover ◽  
General Circulation ◽  
Circulation Model ◽  
Wave Activity ◽  
Dynamical Response ◽  
Mean Flow ◽  
Surface Cooling ◽  
Fall Season ◽  
Annular Mode ◽  
Northern Annular Mode

Abstract Variability in the extent of fall season snow cover over the Eurasian sector has been linked in observations to a teleconnection with the winter northern annular mode pattern. Here, the dynamics of this teleconnection are investigated using a 100-member ensemble of transient integrations of the GFDL atmospheric general circulation model (AM2). The model is perturbed with a simple persisted snow anomaly over Siberia and is integrated from October through December. Strong surface cooling occurs above the anomalous Siberian snow cover, which produces a tropospheric form stress anomaly associated with the vertical propagation of wave activity. This wave activity response drives wave–mean flow interaction in the lower stratosphere and subsequent downward propagation of a negative-phase northern annular mode response back into the troposphere. A wintertime coupled stratosphere–troposphere response to fall season snow forcing is also found to occur even when the snow forcing itself does not persist into winter. Finally, the response to snow forcing is compared in versions of the same model with and without a well-resolved stratosphere. The version with the well-resolved stratosphere exhibits a faster and weaker response to snow forcing, and this difference is tied to the unrealistic representation of the unforced lower-stratospheric circulation in that model.

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