Infrasound transmission in the "shadow zone" observed on balloons in the lower stratosphere

2021 ◽  
Author(s):  
Johan Kero ◽  
Daniel Bowman ◽  
Eli Bird
Keyword(s):  
Acoustic Waves ◽  
Lower Stratosphere ◽  
Acoustic Propagation ◽  
Lower Atmosphere ◽  
Ray Theory ◽  
Acoustic Transmission ◽  
Shadow Zone ◽  
Atmospheric Models ◽  
Acoustic Shadow ◽  
Wind Structure

<p>The temperature and wind structure of the lower atmosphere creates an "acoustic shadow", where acoustic propagation is not expected to occur from a ground based source. This region begins several tens of kilometers from the source and typically ends between one hundred and two hundred kilometers range in the downwind direction of the stratospheric jet. Ground microbarometers still occasionally record acoustic arrivals in this zone due to tropospheric waveguides and/or scattering off of stratospheric structure not accounted for in atmospheric models. However, the properties of these signals in the lower stratosphere (above the tropospheric duct) is unknown, because they have never been previously observed on sensors at these altitudes. Here we present a set of acoustic arrivals from ground explosions recorded on balloons in the lower stratosphere during the mini-BOOSTER campaign in Sweden. Although some of the balloons were in the shadow zone, they still recorded a variety of waveforms from each event. Dual payloads on tethers show that the acoustic waves came from below in these instances. We discuss the provenance of these signals and implications for acoustic transmission in regions where geometric ray theory predicts their absence.</p>

Global upper-atmospheric heating at Jupiter by the recirculation of auroral energy

2021 ◽  
Author(s):  
James O'Donoghue ◽  
Luke Moore ◽  
Tanapat Bhakyapaibul ◽  
Henrik Melin ◽  
Tom Stallard ◽  
...  
Keyword(s):  
Heat Source ◽  
Acoustic Waves ◽  
Temperature Gradients ◽  
Upper Atmosphere ◽  
Global Temperature ◽  
Lower Atmosphere ◽  
Polar Regions ◽  
High Resolution Data ◽  
Coriolis Forces ◽  
Global Circulation Models

<p>Jupiter's upper atmosphere is significantly hotter than expected based on the amount of solar heating it receives. This temperature discrepency is known as the 'energy crisis' due to it's nearly 50-year duration and the fact it also occurs at Saturn, Uranus and Neptune. At Jupiter, magnetosphere-ionosphere coupling gives rise to intense auroral emissions and enormous energy deposition in the magnetic polar regions, so it was presumed long ago that redistribution of this energy could heat the rest of the planet. However, most global circulation models have difficulty redistributing auroral energy globally due to the strong Coriolis forces and ion drag on this rapidly rotating planet. Consequently, other possible heat sources have continued to be studied, such as heating by gravity and acoustic waves emanating from the lower atmosphere. Each global heating mechanism would imprint a unique signature on global temperature gradients, thus revealing the dominant heat source, but these gradients have not been determined due a lack of planet-wide, high-resolution data. The last global map of Jovian upper-atmospheric temperatures was produced using ground-based data taken in 1993, in which the region between 45<sup>o</sup> latitude (north & south) and the poles was represented by just 2 pixels. As a result, those maps did not (or could not) show a clear temperature gradient, and furthermore, they even showed regions of hot atmosphere near the equator, supporting the idea of an equatorial heat source, e.g. gravity and/or acoustic wave heating. Therefore observationally and from a modeling perspective, a concensus has not been reached to date. Here we report new infrared spectroscopy of Jupiter's major upper-atmospheric ion H<sub>3</sub><sup>+</sup>, with a spatial resolution of 2<sup>o</sup> longitude and latitude extending from pole to equator, capable of tracing the global temperature gradients. We find that temperatures decrease steadily from the auroral polar regions to the equator. Further, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed which may be propagating from the aurora. These observations indicate that Jupiter's upper atmosphere is predominantly heated via the redistribution of auroral energy, and therefore that Coriolis forces and ion drag are observably overcome.</p>

scholarly journals Seasonal variation of vertical eddy diffusivity in the troposphere, lower stratosphere and mesosphere over a tropical station

2001 ◽  
Vol 19 (8) ◽  
pp. 975-984 ◽  
Author(s):  
D. Narayana Rao ◽  
M. V. Ratnam ◽  
T. N. Rao ◽  
S. V. B. Rao
Keyword(s):  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Beam Width ◽  
Eddy Diffusivity ◽  
Lower Atmosphere ◽  
Spectral Parameters ◽  
Vhf Radar ◽  
June July ◽  
Vertical Eddy Diffusivity ◽  
Vertical Eddy

Abstract. Long-term VHF radar (53 MHz with 3° beam-width) observations at Gadanki (13.5° N, 79.2° E), India, during the period from September 1995 to August 1999 are used to study monthly, seasonal and annual medians of vertical eddy diffusivity, K in the troposphere, lower stratosphere and mesosphere. First, the spectral width contribution due to non-turbulent effects has been removed for further analysis and the monthly, seasonal medians of K are calculated. The monthly median of K in the troposphere shows maximum and minimum in June-July and November-December, respectively. In general, large values of K are seen up to 10 km and then decrease with height. Larger values of K are observed during monsoon and post-monsoon than in winter and summer. In general, the maximum and minimum values of the annual median of K (in logarithmic values) in the troposphere are found to be 0.25 and - 1.3 m2 s-1 respectively. In the mesosphere, the monthly median of K shows maximum and minimum during June-July and November-December, respectively, similar to the lower atmosphere. The value of K in the mesosphere becomes larger and it increases with height up to 75 km and again decreases above that height. The maximum values are seen during the summer, followed by equinoxes and a minimum during the winter. In general, the maximum and minimum values of K (in logarithmic values) are found to be 0.7 and 0.3 m2 s-1, respectively, in the mesosphere. A comparison of Doppler spectral parameters in different beam directions shows anisotropy in both signal-to- noise ratio (SNR) and spectral widths in the mesosphere, whereas it shows isotropy in SNR and anisotropy in the spectral widths in troposphere and lower stratosphere.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence; waves and tides)

scholarly journals Tropospheric eddy feedback to different stratospheric conditions in idealised baroclinic life cycles

2021 ◽  
Vol 2 (1) ◽  
pp. 111-128
Author(s):  
Philip Rupp ◽  
Thomas Birner
Keyword(s):  
Lower Stratosphere ◽  
Polar Vortex ◽  
Surface Friction ◽  
Life Cycles ◽  
Synoptic Scale ◽  
Final State ◽  
Northern Annular Mode ◽  
Wind Structure ◽  
Basic Set ◽  
Set Up

Abstract. A pronounced signature of stratosphere–troposphere coupling is a robust negative anomaly in the surface northern annular mode (NAM) following sudden stratospheric warming (SSW) events, consistent with an equatorward shift in the tropospheric jet. It has previously been pointed out that tropospheric synoptic-scale eddy feedbacks, mainly induced by anomalies in the lowermost extratropical stratosphere, play an important role in creating this surface NAM signal. Here, we use the basic set-up of idealised baroclinic life cycles to investigate the influence of stratospheric conditions on the behaviour of tropospheric synoptic-scale eddies. Particular attention is given to the enhancement of the tropospheric eddy response by surface friction and the sensitivity to wind anomalies in the lower stratosphere. We find systems that include a tropospheric jet only (modelling post-SSW conditions) to be characterised by an equatorward shift in the tropospheric jet in the final state of the life cycle, relative to systems that include a representation of the polar vortex (mimicking more undisturbed stratospheric wintertime conditions), consistent with the observed NAM response after SSWs. The corresponding relative surface NAM signal is increased if the system includes surface friction, presumably due to a direct coupling of the eddy field at tropopause level to the surface winds. We further show that the jet shift signal observed in our experiments is mainly caused by changes in the zonal wind structure of the lowermost stratosphere, while changes in the wind structure of the middle and upper stratosphere have almost no influence.

scholarly journals Gradient index phononic crystals and metamaterials

Nanophotonics ◽  
2019 ◽  
Vol 8 (5) ◽  
pp. 685-701 ◽  
Author(s):  
Yabin Jin ◽  
Bahram Djafari-Rouhani ◽  
Daniel Torrent
Keyword(s):  
Refractive Index ◽  
Wave Propagation ◽  
Acoustic Waves ◽  
Effective Properties ◽  
Periodic Structures ◽  
Phononic Crystals ◽  
Ray Theory ◽  
Acoustic Metamaterials ◽  
Propagation Of Waves ◽  
At Will

AbstractPhononic crystals and acoustic metamaterials are periodic structures whose effective properties can be tailored at will to achieve extreme control on wave propagation. Their refractive index is obtained from the homogenization of the infinite periodic system, but it is possible to locally change the properties of a finite crystal in such a way that it results in an effective gradient of the refractive index. In such case the propagation of waves can be accurately described by means of ray theory, and different refractive devices can be designed in the framework of wave propagation in inhomogeneous media. In this paper we review the different devices that have been studied for the control of both bulk and guided acoustic waves based on graded phononic crystals.

Absolute intensities of acoustic shadow zone arrivals

2008 ◽  
Vol 123 (5) ◽  
pp. 3464-3464 ◽  
Author(s):  
Lora Van Uffelen ◽  
Peter Worcester ◽  
Matthew Dzieciuch
Keyword(s):  
Shadow Zone ◽  
Acoustic Shadow ◽  
Absolute Intensities

The effect of turbulence and acoustic waves on underwater acoustic propagation

2006 ◽  
Vol 119 (5) ◽  
pp. 3346-3346
Author(s):  
Stefanie E. Wojcik ◽  
William W. Durgin ◽  
Tatiana A. Andreeva
Keyword(s):  
Acoustic Waves ◽  
Acoustic Propagation ◽  
Underwater Acoustic

scholarly journals Climatic variability of the mean flow and stationary planetary waves in the NCEP/NCAR reanalysis data

2008 ◽  
Vol 26 (5) ◽  
pp. 1233-1241 ◽  
Author(s):  
A. Yu. Kanukhina ◽  
E. V. Suvorova ◽  
L. A. Nechaeva ◽  
E. K. Skrygina ◽  
A. I. Pogoreltsev
Keyword(s):  
Lower Stratosphere ◽  
Climatic Variability ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Mean Flow ◽  
The Mean ◽  
The 1960S ◽  
Environmental Prediction

Abstract. NCEP/NCAR (National Center for Environmental Prediction – National Center for Atmospheric Research) data have been used to estimate the long-term variability of the mean flow, temperature, and Stationary Planetary Waves (SPW) in the troposphere and lower stratosphere. The results obtained show noticeable climatic variabilities in the intensity and position of the tropospheric jets that are caused by temperature changes in the lower atmosphere. As a result, we can expect that this variability of the mean flow will cause the changes in the SPW propagation conditions. The simulation of the SPW with zonal wave number m=1 (SPW1), performed with a linearized model using the mean flow distributions typical for the 1960s and for the beginning of 21st century, supports this assumption and shows that during the last 40 years the amplitude of the SPW1 in the stratosphere and mesosphere increased substantially. The analysis of the SPW amplitudes extracted from the geopotential height and zonal wind NCEP/NCAR data supports the results of simulation and shows that during the last years there exists an increase in the SPW1 activity in the lower stratosphere. These changes in the amplitudes are accompanied by increased interannual variability of the SPW1, as well. Analysis of the SPW2 activity shows that changes in its amplitude have a different sign in the northern winter hemisphere and at low latitudes in the southern summer hemisphere. The value of the SPW2 variability differs latitudinally and can be explained by nonlinear interference of the primary wave propagation from below and from secondary SPW2.

STABILITY OF ACOUSTIC PROPAGATION IN 2D DUCT FLOWS: A LOW FREQUENCY APPROACH

2011 ◽  
Vol 21 (05) ◽  
pp. 1121-1151 ◽  
Author(s):  
A.-S. BONNET-BEN DHIA ◽  
M. DURUFLE ◽  
P. JOLY ◽  
L. JOUBERT
Keyword(s):  
Laminar Flow ◽  
Acoustic Waves ◽  
Normal Operator ◽  
Low Frequency ◽  
Acoustic Propagation ◽  
Compressible Fluids ◽  
Well Posedness ◽  
Hydrodynamic Instabilities ◽  
Limit Model

In this paper, we derive a simplified "quasi-1D" limit model for the propagation of low frequency acoustic waves in a laminar flow filling a 2D duct. We analyze the well-posedness of this model in function of the Mach profile of the flow. This can be reduced to the study of the spectrum of a bounded non-normal operator. As a by-product of this analysis, we establish new results for hydrodynamic instabilities of Kelvin–Helmholtz type in compressible fluids.

A Brief Study on the Characteristics of Tropospheric Wind Energy over Wuhan Based on Certain Energy Materials

2011 ◽  
Vol 63-64 ◽  
pp. 519-522 ◽  
Author(s):  
Wei Li ◽  
Hao Ge Ma ◽  
Zhi Wei Cai
Keyword(s):  
Wind Velocity ◽  
Lower Stratosphere ◽  
Meridional Wind ◽  
Wave Activity ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Energy Materials ◽  
Height Range ◽  
Summer Minimum ◽  
Tropospheric Wind

By analysing the wind data observed by radiosonde during 2000-2002 in Wuhan, zonal and meridional wind velocity, wind shear and energy were discussed. A winter maximum and a summer minimum of the zonal wind velocity which pace up and down between the height of 10-15km was found. The weaker variation of the meridional wind reflects the seasonal variation of gravity wave activity in the lower atmosphere. The energy variation show a trend stronger in winter and spring then in other seasons. A winter maximum and a summer minimum in the troposphere and lower stratosphere was also found, which ranged in similar height range as wind velocity. As a result, a strong correlation between horizontal wind velocity and kinetic energy can be infered.

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