scholarly journals Symmetries in Evolving Space-time and Their Connection to High-Frequency Gravity Wave Production

2008 ◽  
Author(s):  
A. W. Beckwith ◽  
Mohamed S. El-Genk
Keyword(s):  
Gravity Wave ◽  
High Frequency ◽  
Space Time

Infrasonic Signal Observation through the Monitoring Network

2014 ◽  
Vol 643 ◽  
pp. 224-227
Author(s):  
Juan Zhao ◽  
Guo Cheng Hao ◽  
Zuo Xun Zeng
Keyword(s):  
Gravity Wave ◽  
Spectrum Analysis ◽  
High Frequency ◽  
Correlation Method ◽  
Monitoring Network ◽  
Travel Speed ◽  
Calculation Error ◽  
Acoustic Gravity Wave ◽  
Earthquake Sources ◽  
Infrasonic Signal

The methods of observing and processing infrasonic signals from earthquake sources are discussed in this paper. The categories of earthquake infrasound are firstly discussed. Spectrum analysis as well as travel speed calculation are used to distinguish high frequency local infrasound from the acoustic-gravity wave. Monitoring network has been established to capture the signals from the atmosphere. Basing on a simplified correlation method, a triangle array made of three sensors can decide the direction of the coming signal, and locate the earthquake sources. The calculation error and steps of further improvement are also discussed at the end of the paper.

scholarly journals Simulation of non-hydrostatic gravity wave propagation in the upper atmosphere

2014 ◽  
Vol 32 (4) ◽  
pp. 443-447 ◽  
Author(s):  
Y. Deng ◽  
A. J. Ridley
Keyword(s):  
Wave Propagation ◽  
Gravity Wave ◽  
High Frequency ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Horizontal Resolution ◽  
Upper Atmosphere ◽  
Cutoff Wavelength ◽  
Frequency Wave

Abstract. The high-frequency and small horizontal scale gravity waves may be reflected and ducted in non-hydrostatic simulations, but usually propagate vertically in hydrostatic models. To examine gravity wave propagation, a preliminary study has been conducted with a global ionosphere–thermosphere model (GITM), which is a non-hydrostatic general circulation model for the upper atmosphere. GITM has been run regionally with a horizontal resolution of 0.2° long × 0.2° lat to resolve the gravity wave with wavelength of 250 km. A cosine wave oscillation with amplitude of 30 m s−1 has been applied to the zonal wind at the low boundary, and both high-frequency and low-frequency waves have been tested. In the high-frequency case, the gravity wave stays below 200 km, which indicates that the wave is reflected or ducted in propagation. The results are consistent with the theoretical analysis from the dispersion relationship when the wavelength is larger than the cutoff wavelength for the non-hydrostatic situation. However, the low-frequency wave propagates to the high altitudes during the whole simulation period, and the amplitude increases with height. This study shows that the non-hydrostatic model successfully reproduces the high-frequency gravity wave dissipation.

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2016 ◽  
Vol 16 (1) ◽  
pp. 35-46 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved.With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, a low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INCs.

scholarly journals Gravity-wave momentum fluxes in the mesosphere over Ascension Island (8° S, 14° W) and the anomalous zonal winds of the semi-annual oscillation in 2002

2016 ◽  
Vol 34 (2) ◽  
pp. 323-330 ◽  
Author(s):  
Andrew C. Moss ◽  
Corwin J. Wright ◽  
Robin N. Davis ◽  
Nicholas J. Mitchell
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
High Frequency ◽  
Wave Forcing ◽  
Zonal Winds ◽  
Ascension Island ◽  
Wind Event ◽  
Momentum Fluxes ◽  
Anomalous Wind ◽  
Wave Induced

Abstract. Anomalously strong westward winds during the first phase of the equatorial mesospheric semi-annual oscillation (MSAO) have been attributed to unusual filtering conditions producing exceptional gravity-wave fluxes. We test this hypothesis using meteor-radar measurements made over Ascension Island (8° S, 14° W). An anomalous wind event in 2002 of −85.5 ms−1 occurred simultaneously with the momentum fluxes of high-frequency gravity waves reaching the largest observed westward values of −29 m2 s−2 and strong westward wind accelerations of −510 ms−1 day−1. However, despite this strong wave forcing during the event, no unusual filtering conditions or significant increases in wave-excitation proxies were observed. Further, although strong westward wave-induced accelerations were also observed during the 2006 MSAO first phase, there was no corresponding simultaneous response in westward wind. We thus suggest that strong westward fluxes/accelerations of high-frequency gravity waves are not always sufficient to produce anomalous first-phase westward MSAO winds and other forcing may be significant.

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2015 ◽  
Vol 15 (6) ◽  
pp. 8771-8799 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INC.

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