Two-frequency acoustic-gravitational waves, simulation of satellite measurements

The theory of acoustic gravity waves (AGW) considers free disturbances of the atmosphere within the framework of a single-frequency approach. In this case, the theory implies the existence of two separate types of waves with different natural frequencies - acoustic and gravitational. In the single-frequency approach, wave fluctuations of density, temperature, and velocity are related to each other through the spectral characteristics of the wave, and these relationships are unchanged. However, satellite observations of AGW parameters cannot always be explained within the framework of a single-frequency approach. This paper presents a two-frequency approach to the study of AGWs using the model of two coupled oscillators. It is shown that the perturbed movements of the elementary volume of the medium occur simultaneously at two natural frequencies. In this case, the connections between the wave fluctuations of the parameters are determined by the initial conditions, which can be arbitrary. Solutions in real functions for an isothermal atmosphere are obtained. The conditions under which single-frequency AGWs are obtained from the general two-frequency solution are investigated. The AGW waveforms measured from the satellite for velocities and displacements in single-frequency and dual-frequency modes are numerically simulated. The results of simulating two-frequency AGWs agree with the data of satellite measurements. Two-frequency AGWs are not always implemented at two different frequencies. It is shown that when the frequencies approach each other, the beat effect occurs and two closely related modes become indistinguishable. At the same wavelength, they have one center frequency and one phase velocity. The main feature of the two-frequency approach to the study of AGW is the expansion of the relationships between the wave parameters of the medium. This makes it possible to achieve satisfactory agreement of the model waveforms with the data of satellite measurements. Thus, the use of a two-frequency AGW treatment opens up new possibilities in the interpretation of experimental data.

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Acoustic-gravity waves in a viscous and thermally conducting isothermal atmosphere

International Journal of Mathematics and Mathematical Sciences ◽

10.1155/s0161171295000469 ◽

1995 ◽

Vol 18 (2) ◽

pp. 371-382 ◽

Cited By ~ 4

Author(s):

H. Y. Alkahby

Keyword(s):

Gravity Waves ◽

Attenuation Factor ◽

Volume Effect ◽

Temperature Perturbation ◽

Oscillatory Process ◽

Acoustic Gravity Waves ◽

Perturbation Problem ◽

The One ◽

Thermally Conducting ◽

Isothermal Atmosphere

In this paper we will investigate the effect of Newtonian cooling on the propagation of acoustic-gravity waves in a viscous and thermally conducting isothermal atmosphere for large Prandtl number and for an arbitrary values of Newtonian cooling coefficient. This problem leads to a singular perturbation problem which is solved by matching inner and outer approximations. It is shown that the viscosity creates an absorbing and reflecting layer. Below it the oscillatory process is adiabatic, for small Newtonian cooling coefficient, and above it the solution will decay to constant before it is influenced by the effect of the thermal conductivity. Newtonian cooling is a volume effect and influences mainly the lower adiabatic region, in which it causes attenuation in the amplitude of the wave. Finally it is shown that when Newtonian cooling coefficient goes to infinity it acts directly to eliminate the temperature perturbation associated with the wave and the attenuation factor in the amplitude of the wave. Accordingly the wavelength changes to the one consistent with the Newtonian sound speed. The reflection coefficient and the attenuation factor of the amplitude of the wave are derived for all values of Newtonian cooling coefficient.

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Relationships between ocean bottom noise and the environment

Bulletin of the Seismological Society of America ◽

10.1785/bssa0840061991 ◽

1994 ◽

Vol 84 (6) ◽

pp. 1991-2007 ◽

Cited By ~ 2

Author(s):

Jeffrey M. Babcock ◽

Barry A. Kirkendall ◽

John A. Orcutt

Keyword(s):

Gravity Waves ◽

Spectral Characteristics ◽

Low Frequency ◽

Environmental Data ◽

Single Frequency ◽

Frequency Noise ◽

Ocean Bottom ◽

Double Frequency ◽

Frequency Peak ◽

Northern Atlantic

Abstract Observations of ocean bottom low-frequency noise and surface environmental data over a period of 27 days in the northern Atlantic during the SAMSON and SWADE experiments reveal how closely related the noise is to meteorological conditions. Double-frequency microseisms produced by nonlinear interactions of storm-induced surface gravity waves are especially evident in the frequency band 0.16 to 0.3 Hz and show a high variability in both amplitude and peak frequencies. Bifurcated at times, the peak that characterizes the microseism band contains local and distant or “teleseismic” components, which are generated at different locations. Weather and storm fetch appear to be the major contributions to the size and shape of microseism spectra. Storm development on the sea surface is associated with progressively lower microseism frequencies along with a concurrent increase in amplitude. The single-frequency microseism peak is a continuous feature and is observed to portray the same time-dependent spectral characteristics as the portion of the double-frequency peak associated with distant storms. Coherence studies confirm that both peaks (single and teleseismic double) originate at a distant source. These peaks are generated at roughly the same location with some storm component over the coastline.

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Propagation of Acoustic‐Gravity Waves from a Small Source in an Isothermal Atmosphere

The Journal of the Acoustical Society of America ◽

10.1121/1.2142479 ◽

1963 ◽

Vol 35 (5) ◽

pp. 795-795 ◽

Cited By ~ 2

Author(s):

Allan D. Pierce

Keyword(s):

Gravity Waves ◽

Acoustic Gravity Waves ◽

Isothermal Atmosphere

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Mean spectral characteristics of acoustic gravity waves in the thermosphere-ionosphere determined from Dynasonde data

Radio Science ◽

10.1002/2015rs005823 ◽

2016 ◽

Vol 51 (3) ◽

pp. 213-222 ◽

Cited By ~ 7

Author(s):

Cătălin Negrea ◽

Nikolay A. Zabotin

Keyword(s):

Gravity Waves ◽

Spectral Characteristics ◽

Acoustic Gravity Waves

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Evaluation of the Sensitivity of Medicane Ianos to Model Microphysics and Initial Conditions Using Satellite Measurements

Remote Sensing ◽

10.3390/rs13244984 ◽

2021 ◽

Vol 13 (24) ◽

pp. 4984

Author(s):

Albert Comellas Prat ◽

Stefano Federico ◽

Rosa Claudia Torcasio ◽

Leo Pio D’Adderio ◽

Stefano Dietrich ◽

...

Keyword(s):

Initial Conditions ◽

Surface Wind ◽

Wrf Model ◽

The Other ◽

Mature Stage ◽

Dual Frequency ◽

Satellite Measurements ◽

Microphysics Scheme ◽

Mature Phase ◽

Sea Surface Wind

Tropical-like cyclone (TLC or medicane) Ianos formed during mid-September 2020 over the Southern Mediterranean Sea, and, during its mature stage on days 17–18, it affected southern Italy and especially Greece and its Ionian islands, where it brought widespread disruption due to torrential rainfall, severe wind gusts, and landslides, causing casualties. This study performs a sensitivity analysis of the mature phase of TLC Ianos with the WRF model to different microphysics parameterization schemes and initial and boundary condition (IBC) datasets. Satellite measurements from the Global Precipitation Measurement Mission-Core Observatory (GPM-CO) dual-frequency precipitation radar (DPR) and the Advanced Scatterometer (ASCAT) sea-surface wind field were used to verify the WRF model forecast quality. Results show that the model is most sensitive to the nature of the IBC dataset (spatial resolution and other dynamical and physical differences), which better defines the primary mesoscale features of Ianos (low-level vortex, eyewall, and main rainband structure) when using those at higher resolution (~25 km versus ~50 km) independently of the microphysics scheme, but with the downside of producing too much convection and excessively low minimum surface pressures. On the other hand, no significant differences emerged among their respective trajectories. All experiments overestimated the vertical extension of the main rainbands and display a tendency to shift the system to the west/northwest of the actual position. Especially among the experiments with the higher-resolution IBCs, the more complex WRF microphysics schemes (Thompson and Morrison) tended to outperform the others in terms of rain rate forecast and most of the other variables examined. Furthermore, WSM6 showed a good performance while WDM6 was generally the least accurate. Lastly, the calculation of the cyclone phase space diagram confirmed that all simulations triggered a warm-core storm, and all but one also exhibited axisymmetry at some point of the studied lifecycle.

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