Turbulent parameters in the middle atmosphere: Theoretical estimates deduced from a gravity-wave resolving general circulation model

2021 ◽  
Keyword(s):  
Gravity Wave ◽  
General Circulation Model ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Small Scale ◽  
Scaling Analysis ◽  
Stratified Turbulence ◽  
Atmospheric Flow ◽  
Diffusion Scheme

Abstract We present a scaling analysis for the stratified turbulent and small-scale turbulent regimes of atmospheric flow with emphasis on the mesosphere. We distinguish rotating-stratified macroturbulence turbulence (SMT), stratified turbulence (ST), and small-scale isotropic Kolmogorov turbulence (KT), and we specify the length and time scales and the characteristic velocities for these regimes. It is shown that the buoyancy scale (Lb) and the Ozmidov scale (Lo) are the main parameters that describe the transition from SMT to KT. We employ the buoyancy Reynolds number and horizontal Froude number to characterize ST and KT in the mesosphere. This theory is applied to simulation results from a high-resolution general circulation model with a Smagorinsky-type turbulent diffusion scheme for the sub-grid scale parameterization. The model allows us to derive the turbulent root-mean-square (RMS) velocity in the KT regime. It is found that the turbulent RMS velocity has a single maximum in summer and a double maximum in winter months. The secondary maximum in the winter MLT we associate with a secondary gravity wave breaking phenomenon. The turbulent RMS velocity results from the model agree well with Full Correlation Analyses based on MF-radar measurements. A new scaling for the mesoscale horizontal velocity based on the idea of direct energy cascade in masoscales is proposed. The latter findings for mesoscale and small-scale characteristic velocities supports the idea proposed in this research that mesoscale and small-scale dynamics in the mesosphere are governed by SMT, ST, and KT in the statistical average.

scholarly journals Southern Hemisphere Extratropical Gravity Wave Sources and Intermittency Revealed by a Middle-Atmosphere General Circulation Model

2016 ◽  
Vol 73 (3) ◽  
pp. 1335-1349 ◽  
Author(s):  
Simon P. Alexander ◽  
Kaoru Sato ◽  
Shingo Watanabe ◽  
Yoshio Kawatani ◽  
Damian J. Murphy
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
General Circulation Model ◽  
Gravity Waves ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Absolute Gravity ◽  
Atmosphere General Circulation Model ◽  
Time Of Year

Abstract Southern Hemisphere extratropical gravity wave activity is examined using simulations from a free-running middle-atmosphere general circulation model called Kanto that contains no gravity wave parameterizations. The total absolute gravity wave momentum flux (MF) and its intermittency, diagnosed by the Gini coefficient, are examined during January and July. The MF and intermittency results calculated from the Kanto model agree well with results from satellite limb and superpressure balloon observations. The analysis of the Kanto model simulations indicates the following results. Nonorographic gravity waves are generated in Kanto in the frontal regions of extratropical depressions and around tropopause-level jets. Regions with lower (higher) intermittency in the July midstratosphere become more (less) intermittent by the mesosphere as a result of lower-level wave removal. The gravity wave intermittency is low and nearly homogeneous throughout the SH middle atmosphere during January. This indicates that nonorographic waves dominate at this time of year, with sources including continental convection as well as oceanic depressions. Most of the zonal-mean MF at 40°–65°S in January and July is due to gravity waves located above the oceans. The zonal-mean MF at lower latitudes in both months has a larger contribution from the land regions but the fraction above the oceans remains larger.

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.

Can we improve gravity wave parameterizations by imposing sources at all altitudes in the atmosphere?

2020 ◽  
Author(s):  
Bruno Ribstein ◽  
Christophe Millet ◽  
Francois Lott ◽  
Alvaro de la Camara
Keyword(s):  
Gravity Wave ◽  
General Circulation Model ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Circulation Model ◽  
Reanalysis Data ◽  
Inertial Waves ◽  
Vertical Propagation

<p>A multiwave non-orographic gravity wave (GW) scheme is adapted to represent waves of small intrinsic phase speed and sources located at all altitudes in the troposphere and middle atmosphere. Using reanalysis data, these changes impose larger amplitude saturated waves everywhere in the middle atmosphere, which permits to produce more realistic GW vertical spectra than when the phase speeds are large and the sources are in the troposphere only. The same scheme, tested online in the Laboratoire de Météorologie Dynamique Zoom(LMDz) general circulation model, performs at least as well as the operational non-orographic GW scheme.  Some modest benefits are seen, for instance, in the equatorial tilt with altitude of the winter jets in the middle atmosphere. Although the scheme includes the effects of inertial waves, which are more and more often detected in the mesosphere, the configuration that gives a reasonable climatology in LMDz hinders the vertical propagation of these parameterized waves and do not generally reach mesospheric altitudes.</p>

Calculating the Natural Atmospheric Radiation Using the General Circulation Model of the Earth’s Lower and Middle Atmosphere

2020 ◽  
Vol 12 (5) ◽  
pp. 803-815
Author(s):  
B. N. Chetverushkin ◽  
I. V. Mingalev ◽  
E. A. Fedotova ◽  
K. G. Orlov ◽  
V. M. Chechetkin ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Atmospheric Radiation

Modeling Tropical Cyclones in a Changing Climate

2016 ◽  
Author(s):  
Enrico Scoccimarro
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
General Circulation Model ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
Climate System ◽  
Ocean Dynamics ◽  
Small Scale ◽  
Computational Power

Tropical cyclones (TCs) in their most intense expression (hurricanes or typhoons) are the main natural hazards known to humankind. The impressive socioeconomic consequences for countries dealing with TCs make our ability to model these organized convective structures a key issue to better understanding their nature and their interaction with the climate system. The destructive effects of TCs are mainly caused by three factors: strong wind, storm surge, and extreme precipitation. These TC-induced effects contribute to the annual worldwide damage of the order of billions of dollars and a death toll of thousands of people. Together with the development of tools able to simulate TCs, an accurate estimate of the impact of global warming on TC activity is thus not only of academic interest but also has important implications from a societal and economic point of view. The aim of this article is to provide a description of the TC modeling implementations available to investigate present and future climate scenarios. The two main approaches to dynamically model TCs under a climate perspective are through hurricane models and climate models. Both classes of models evaluate the numerical equations governing the climate system. A hurricane model is an objective tool, designed to simulate the behavior of a tropical cyclone representing the detailed time evolution of the vortex. Considering the global scale, a climate model can be an atmosphere (or ocean)-only general circulation model (GCM) or a fully coupled general circulation model (CGCM). To improve the ability of a climate model in representing small-scale features, instead of a general circulation model, a regional model (RM) can be used: this approach makes it possible to increase the spatial resolution, reducing the extension of the domain considered. In order to be able to represent the tropical cyclone structure, a climate model needs a sufficiently high horizontal resolution (of the order of tens of kilometers) leading to the usage of a great deal of computational power. Both tools can be used to evaluate TC behavior under different climate conditions. The added value of a climate model is its ability to represent the interplay of TCs with the climate system, namely two-way relationships with both atmosphere and ocean dynamics and thermodynamics. In particular, CGCMs are able to take into account the well-known feedback between atmosphere and ocean components induced by TC activity and also the TC–related remote impacts on large-scale atmospheric circulation. The science surrounding TCs has developed in parallel with the increasing complexity of the mentioned tools, both in terms of progress in explaining the physical processes involved and the increased availability of computational power. Many climate research groups around the world, dealing with such numerical models, continuously provide data sets to the scientific community, feeding this branch of climate change science.

scholarly journals On the Gravity Wave Forcing during the Southern Stratospheric Final Warming in LMDZ

2016 ◽  
Vol 73 (8) ◽  
pp. 3213-3226 ◽  
Author(s):  
Alvaro de la Cámara ◽  
François Lott ◽  
Valérian Jewtoukoff ◽  
Riwal Plougonven ◽  
Albert Hertzog
Keyword(s):  
Gravity Wave ◽  
General Circulation ◽  
Climate Models ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
High Amplitude ◽  
Austral Spring ◽  
Wave Forcing ◽  
Stratospheric Final Warming ◽  
Good Agreement

Abstract The austral stratospheric final warming date is often predicted with substantial delay in several climate models. This systematic error is generally attributed to insufficient parameterized gravity wave (GW) drag in the stratosphere around 60°S. A simulation with a general circulation model [Laboratoire de Météorologie Dynamique zoom model (LMDZ)] with a much less pronounced bias is used to analyze the contribution of the different types of waves to the dynamics of the final warming. For this purpose, the resolved and unresolved wave forcing of the middle atmosphere during the austral spring are examined in LMDZ and reanalysis data, and a good agreement is found between the two datasets. The role of parameterized orographic and nonorographic GWs in LMDZ is further examined, and it is found that orographic and nonorographic GWs contribute evenly to the GW forcing in the stratosphere, unlike in other climate models, where orographic GWs are the main contributor. This result is shown to be in good agreement with GW-resolving operational analysis products. It is demonstrated that the significant contribution of the nonorographic GWs is due to highly intermittent momentum fluxes produced by the source-related parameterizations used in LMDZ, in qualitative agreement with recent observations. This yields sporadic high-amplitude GWs that break in the stratosphere and force the circulation at lower altitudes than more homogeneously distributed nonorographic GW parameterizations do.

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