scholarly journals SMLTM simulations of the diurnal tide: comparison with UARS observations

1997 ◽  
Vol 15 (9) ◽  
pp. 1187-1197 ◽  
Author(s):  
R. A. Akmaev ◽  
V. A. Yudin ◽  
D. A. Ortland
Keyword(s):  
Gravity Wave ◽  
Seasonal Variations ◽  
Lower Thermosphere ◽  
Lower Boundary ◽  
Eddy Diffusion ◽  
Lower Atmosphere ◽  
Diurnal Tide ◽  
Tidal Waves ◽  
Dominant Component ◽  
Dynamics Simulations

Abstract. Wind and temperature observations in the mesosphere and lower thermosphere (MLT) from the Upper Atmosphere Research Satellite (UARS) reveal strong seasonal variations of tides, a dominant component of the MLT dynamics. Simulations with the Spectral mesosphere/lower thermosphere model (SMLTM) for equinox and solstice conditions are presented and compared with the observations. The diurnal tide is generated by forcing specified at the model lower boundary and by in situ absorption of solar radiation. The model incorporates realistic parameterizations of physical processes including various dissipation processes important for propagation of tidal waves in the MLT. A discrete multi-component gravity-wave parameterization has been modified to account for seasonal variations of the background temperature. Eddy diffusion is calculated depending on the gravity-wave energy deposition rate and stability of the background flow. It is shown that seasonal variations of the diurnal-tide amplitudes are consistent with observed variations of gravity-wave sources in the lower atmosphere.

scholarly journals Enhanced gravity-wave activity and interhemispheric coupling during the MaCWAVE/MIDAS northern summer program 2002

2006 ◽  
Vol 24 (4) ◽  
pp. 1175-1188 ◽  
Author(s):  
E. Becker ◽  
D. C. Fritts
Keyword(s):  
Gravity Wave ◽  
Rossby Wave ◽  
Lower Thermosphere ◽  
Wave Activity ◽  
Lower Atmosphere ◽  
Summer Program ◽  
Latent Heating ◽  
Austral Winter ◽  
Northern Summer ◽  
Mesosphere And Lower Thermosphere

Abstract. We present new sensitivity experiments that link observed anomalies of the mesosphere and lower thermosphere at high latitudes during the MaCWAVE/MIDAS summer program 2002 to enhanced planetary Rossby-wave activity in the austral winter troposphere. We employ the same general concept of a GCM having simplified representations of radiative and latent heating as in a previous study by Becker et al. (2004). In the present version, however, the model includes no gravity wave (GW) parameterization. Instead we employ a high vertical and a moderate horizontal resolution in order to describe GW effects explicitly. This is supported by advanced, nonlinear momentum diffusion schemes that allow for a self-consistent generation of inertia and mid-frequency GWs in the lower atmosphere, their vertical propagation into the mesosphere and lower thermosphere, and their subsequent dissipation which is induced by prescribed horizontal and vertical mixing lengths as functions of height. The main anomalies in northern summer 2002 consist of higher temperatures than usual above 82 km, an anomalous eastward mean zonal wind between 70 and 90 km, an altered meridional flow, enhanced turbulent dissipation below 80 km, and enhanced temperature variations associated with GWs. These signals are all reasonably described by differences between two long-integration perpetual model runs, one with normal July conditions, and another run with modified latent heating in the tropics and Southern Hemisphere to mimic conditions that correspond to the unusual austral winter 2002. The model response to the enhanced winter hemisphere Rossby-wave activity has resulted in both an interhemispheric coupling through a downward shift of the GW-driven branch of the residual circulation and an increased GW activity at high summer latitudes. Thus a quantitative explanation of the dynamical state of the northern mesosphere and lower thermosphere during June-August 2002 requires an enhanced Lorenz energy cycle and correspondingly enhanced GW sources in the troposphere, which in the model show up in both hemispheres.

scholarly journals Variability of Gravity Wave Effects on the Zonal Mean Circulation and Migrating Terdiurnal Tide as Studied With the Middle and Upper Atmosphere Model (MUAM2019) Using a Nonlinear Gravity Wave Scheme

2020 ◽  
Vol 7 ◽  
Author(s):  
Friederike Lilienthal ◽  
Erdal Yiğit ◽  
Nadja Samtleben ◽  
Christoph Jacobi
Keyword(s):  
Gravity Wave ◽  
Strong Dependence ◽  
Lower Thermosphere ◽  
Upper Atmosphere ◽  
Lower Atmosphere ◽  
Small Scale ◽  
Source Level ◽  
Atmosphere Model ◽  
Hemisphere Winter ◽  
Nonlinear Gravity

Implementing a nonlinear gravity wave (GW) parameterization into a mechanistic middle and upper atmosphere model, which extends to the lower thermosphere (160 km), we study the response of the atmosphere in terms of the circulation patterns, temperature distribution, and migrating terdiurnal solar tide activity to the upward propagating small-scale internal GWs originating in the lower atmosphere. We perform three test simulations for the Northern Hemisphere winter conditions in order to assess the effects of variations in the initial GW spectrum on the climatology and tidal patterns of the mesosphere and lower thermosphere. We find that the overall strength of the source level momentum flux has a relatively small impact on the zonal mean climatology. The tails of the GW source level spectrum, however, are crucial for the lower thermosphere climatology. With respect to the terdiurnal tide, we find a strong dependence of tidal amplitude on the induced GW drag, generally being larger when GW drag is increased.

Seasonal variations of the diurnal tide induced by gravity wave filtering

1998 ◽  
Vol 25 (7) ◽  
pp. 943-946 ◽  
Author(s):  
H. G. Mayr ◽  
J. G. Mengel ◽  
K. L. Chan ◽  
H. S. Porter
Keyword(s):  
Gravity Wave ◽  
Seasonal Variations ◽  
Diurnal Tide

scholarly journals Estimates of eddy turbulence consistent with seasonal variations of atomic oxygen and its possible role in the seasonal cycle of mesopause temperature

2010 ◽  
Vol 28 (11) ◽  
pp. 2103-2110 ◽  
Author(s):  
M. N. Vlasov ◽  
M. C. Kelley
Keyword(s):  
Diffusion Coefficient ◽  
Gravity Waves ◽  
Seasonal Variations ◽  
Atomic Oxygen ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Downward Motion ◽  
Adiabatic Cooling ◽  
Eddy Diffusion Coefficient ◽  
The Impact

Abstract. According to current understanding, adiabatic cooling and heating induced by the meridional circulation driven by gravity waves is the major process for the cold summer and warm winter polar upper mesosphere. However, our calculations show that the upward/downward motion needed for adiabatic cooling/heating of the summer/winter polar mesopause simultaneously induces a seasonal variation in both the O maximum density and the altitude of the [O] peak that is opposite to the observed variables generalized by the MSISE-90 model. It is usually accepted that eddy turbulence can produce the [O] seasonal variations. Using this approach, we can infer the eddy diffusion coefficient for the different seasons. Taking these results and experimental data on the eddy diffusion coefficient, we consider in detail and estimate the heating and cooling caused by eddy turbulence in the summer and winter polar upper mesosphere. The seasonal variations of these processes are similar to the seasonal variations of the temperature and mesopause. These results lead to the conclusion that heating/cooling by eddy turbulence is an important component in the energy budget and that adiabatic cooling/heating induced by upward/downward motion cannot dominate in the mesopause region. Our study shows that the impact of the dynamic process, induced by gravity waves, on [O] distributions must be included in models of thermal balance in the upper mesosphere and lower thermosphere (MLT) for a consistent description because (a) the [O] distribution is very sensitive to dynamic processes, and (b) atomic oxygen plays a very important role in chemical heating and infrared cooling in the MLT. To our knowledge, this is the first attempt to consider this aspect of the problem.

scholarly journals A study into the effect of the diurnal tide on the structure of the background mesosphere and thermosphere using the new coupled middle atmosphere and thermosphere (CMAT) general circulation model

2002 ◽  
Vol 20 (2) ◽  
pp. 225-235 ◽  
Author(s):  
M. J. Harris ◽  
N. F. Arnold ◽  
A. D. Aylward
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Atomic Oxygen ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Diurnal Tide ◽  
Temperature Structure ◽  
The Mean

Abstract. A new coupled middle atmosphere and thermosphere general circulation model has been developed, and some first results are presented. An investigation into the effects of the diurnal tide upon the mean composition, dynamics and energetics was carried out for equinox conditions. Previous studies have shown that tides deplete mean atomic oxygen in the upper mesosphere-lower thermosphere due to an increased recombination in the tidal displaced air parcels. The model runs presented suggest that the mean residual circulation associated with the tidal dissipation also plays an important role. Stronger lower boundary tidal forcing was seen to increase the equatorial local diurnal maximum of atomic oxygen and the associated 0(1S) 557.7 nm green line volume emission rates. The changes in the mean background temperature structure were found to correspond to changes in the mean circulation and exothermic chemical heating.Key words. Atmospheric composition and structure (middle atmosphere – composition and chemistry) Meterology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

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