Folie 1

1
Simulating the propagation of infrasound in the
atmosphere
Lars Ceranna
Infrasound Technology Workshop, La Jolla, 27-30
Oct 2003
2
Overview

• Introduction
• Equation of motion, the aeroacoustic equations
• Chebyshev pseudospectral method
• Examples
• Conclusions

3
Registration of the Bavarian Bolide at IS26
filtered between 0.1 and 4 Hz
sonogram at I26H3
Introduction
4
Detection of the Bavarian Bolide at IS26
signal detector
fk-analysis
Introduction
5
Location of the Bavarian Bolide

• European Fireball Network all-sky cameras
• IMS Infrasound Network IS26-array

• source location
• 6-Apr-2002 202018 (UT)
• 47.51N / 10.91E, HS21 km
• 47.53N / 10.85E, HS16 km
• relative to IS26
• D2.32 / 258 km
• b 235.5
• dt1,213.5 15.0 min

Introduction
6
Forward modeling ray-tracing and reflectivity (I)
1-D velocity model
Introduction
7
Forward modeling ray-tracing and reflectivity
(II)
1-D velocity model
Introduction
8
Equation of motion in a moving media
aeroacoustic equations

• Assumptions
• linearization to governing equations
• background flow (wind) is stationary

• S - acoustic entropy
• P - pressure variation
• P0 - initial pressure
• - density variation
• 0 - density
• c0 - phase velocity
• ui - background flow
• ui - particle velocity

Equation of motion
9
Spherical coordinates rotationally symmetric
approach
Equation of motion
10
Chebyshev pseudospectral method

• two-dimensional fields are defined at
  Gauss-Lobatto points
• corresponding to the solution of the
  Sturm-Liuoville problem
• numerical accuracy is achieved within the model
  and at the boundaries
• spatial derivatives are computed using the matrix
  multiply method
• propagation in time is obtained by applying a 3rd
  order Runge-Kutta scheme

Chebyshev pseudospectral method
11
Reference velocity model US standard atmosphere
HS0 km
HS20 km
Q0 10 Hmax200 km
Chebyshev pseudospectral method
12
Synthetic barograms
HS0 km
HS20 km
Chebyshev pseudospectral method
13
Example (I) Chemical explosion in Toulouse
source location 21-Sep-2001 081757
(UT) 43.62N / 1.37E, HS0 km relative to
IS26 D10.02 / 1114 km b242.2
Examples
14
Registration and detection at IS26
filtered between 0.3 and 1.2 Hz
fk-analysis
Examples
15
Numerical modeling models snapshots
reference model
1D radial wind
Q0 12 Hmax170 km
Examples
16
Numerical modeling synthetic sections
reference model
1D radial wind model
Examples
17
Waveform comparison
synthetic barograms
envelopes
Examples
18
Example (II) Bavarian Bolide
source location 06-Apr-2002 202018
(UT) 47.51N / 10.91E, HS21 km relative to
IS26 D2.32 / 258 km b235.5
Examples
19
Numerical modeling models waveforms

• What kind of phases are the first two onsets?
• How can the high amplitudes of It-phases be
  reduced?

Examples
20
Character of the first two onsets
guided waves in the stratospheric/tropospheric low
-velocity zone
Examples
21
Amplitude reduction of thermospheric refractions
decreased density
quality factor
Examples
22
Comparison of envelopes
initial approach
introduced modifications
Examples
23
Conclusions
Conclusions