Transcript 6-05b ReVelle - Laboratory for Atmospheric Acoustics

Infrasonic Technology Workshop
November 3-7, 2008, Bermuda, U.K.
Session 6: Infrasound from Geophysical Sources
Presentation:
INFRASOUND FROM 2008TC3 ON 7 OCTOBER 2008
D.O. ReVelle
EES-17, Geophysics Group, Los Alamos National Laboratory
Los Alamos, New Mexico 87545 USA
P.G. Brown, W.N. Edwards and E. A. Silber
Physics and Astronomy Department, University of Western Ontario
London, Ontario, Canada N6A 3K7
Summary of Presentation
• Introduction and Overview
 Some recent bolides
 The Meteor-Bolide Interaction Spectrum
• Astronomically Predicted Impact Location of 2008TC3: N. Sudan
• U.S. Government Public Release: Satellite Detection of 2008TC3
 Geographic location and breakup height details
 Amount of light radiated in the optical, etc.
• Entry Dynamics Modeling Summary
 Direct and Inverse Entry Modeling Approaches
• Direct TPFM Entry Modeling Summary and Results
• Inverse Entry Modeling Results Summary and Results
• Summary and Conclusions
Bolide Diversity: Recent Polish fireball,
Moravka and Tagish Lake
Polish fireball: 13 June 2006;
17:15 UTCPersistent Smoke Trail
Moravka – Janov Video
Tagish Lake smoke trail
with solar illumination
Telescopic Image from Elginfield Observatory
Meteor-Atmosphere Interaction Spectrum
Brightness
Sun
???
Faintest stars Venus Full moon
100.0
Continuum fluid flow
Mass
Loss
(%)
 and 
meteoroids
Super-bolides
Free
Shock
molecule waves
flow
Shooting
stars
Ordinary
bolides
Micrometeoroids
Velocity
dependent
No light
from
ablation
and no
sound
Light, light and
but no weak
sound infrasound
at the
ground
0.0
1 m
Intense
Impact and
explosive
cratering
Electrophonic
sounds
Tsunami formation
following oceanic
impact
Intense light and
strong infrasound and
internal atmospheric
gravity and Lamb
waves
1m
Size
Tektite
strewnfields
Dinosaur
Extinction
(TertiaryCretaceous
Boundary)
Climate
change
10 km
Projected Impact Spot
Courtesy of Euromet: Meteosat Image of Impact
of 2008TC3: Near-IR channel at 3.90 m
US Government Public Announcement
of Satellite Detection of 2008TC3
• US Government Official Announcement: Public Release of satellite
information for Asteroid 2008TC3 and Bolide Detection
• Sensors aboard US satellites detected the impact of a bolide over
Africa on 7 October 2008 at 02:45:40 UT. The initial observation
put the object at 65.4 km altitude at:
 20.9 deg N. latitude, 31.4 deg E. longitude.
• The object detonated at an altitude of approximately 37 km
at:
 20.8 deg N. latitude, 32.2 deg E. longitude.
• The total radiated energy was approximately 4.01011 joules. This
is equivalent to approximately 0.10 kT of radiated optical energy
(assuming a 6000 K black body).
• This event origin time is completely confirmed by infrasonic array
detections made at I32 in Kenya and at I31 in Kazakhstan.
Entry Information and Key
Modeling Assumptions Made for 2008TC3
• Entry into the sensible atmosphere from a westerly direction and
terminated over eastern Africa: September 7, 2008
 Predicted Impact: Latitude 20.855 N; Longitude 31.697 E
• Entry angle of radiant: 70.9  from the zenith (Observed)
• Entry velocity: 12.82 km/s (Observed)
• Initial radius  2.0 meters (from astronomical/astrometric data)
• Hypersonic Aerodynamic Entry Modeling:
 DIRECT (Top-down) solutions
 INVERSE (Bottom-up) solutions
 Modeling: Homogeneous or Porous Meteoroid Structure
 Spherical unchanging shape (  2/3) assumed throughout
 In TPFM DIRECT Entry Model runs, 64 fragments allowed
 In INVERSE Entry Model runs- No fragmentation allowed
Entry Modeling Approaches-I
• DIRECT TPFM (Triggered Progressive Fragmentation Model)Entry modeling (ReVelle, 2005, 2007)
 Top-down Approach
 Initial size, velocity, entry angle, shape, shape change, bulk
density (Bolide group designation for homogeneous bodiesDiscrete designation or porous meteoroids within a continuum
of possible bulk density values), etc. assumed and:
 Detailed stagnation point heat transfer calculations performed
using:
• Radiation, convection/conduction
 Mechanical, stagnation point progressive fragmentation model
utilized for either homogeneous or porous meteoroids with
differing “breaking” strengths assigned for each type.
Entry Modeling Approaches- II
• INVERSE entry modeling (McIntosh, 1970; ReVelle, 1979, 2005)
 Bottom-Up Approach
 Mean shape, entry angle, ablation parameters specified with
each group- NO fragmentation parameters utilized
 Bolide groups- Homogeneous with only discrete bulk density
values with heating parameters specified for each group
 Using either (all parameters observed at or near the end of the
luminous flight):
• Crater field size at a specified height above the surface used
and/or:
• End height (as in this case):
• Initial parameters iterated in order to determine if solutions exist:
 Initial velocity and initial radius (spherical unchanging shape)
 Wave drag coefficient shape factor product, including errors
2008TC3 Direct Entry Inputs
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1.00
12.82
70.90
32.0
1.209
0.6667
4.605
1.0
1.0
1.0
1.0
0.0
1.0
0.0
0.70
RINF Initial bolide/meteor radius (m) [= 0.000001 - 1000.0]
VINF Initial velocity (km/s) [=11.2 - 73.0]
ZR
Entry angle to vertical at top of atmosphere: deg [=0.0 - 80.0]
NBMX Maximum number of pieces of fragmentation [=1 - 1000]
SFINF Shape factor (area/ volume**2/3) 1.209= sphere [1.209 - 2.0]
MU
Shape change factor 2/3= no change [-3 to 2/3]
D
Kinetic energy left at end height [2.303 - 4.605] i.e. [10 - 1%]
BRKTST Allow breakup 0= no; 1= yes [0 or 1]
FRGTST Fragments in wake 0= remain; 1= stay with body [0 or 1]
PORTST Allow porous materials 0= no-porosity; 1= porous [0 or 1]
SIGTEST Ablation parameter 0= no change; 1= full change [0 or 1]
MUTEST Shape change factor 0= constant; 1= variable [0 or 1]
ISTHRM Vertical structure 0= isothermal; 1= non-isothermal [0 or 1]
RHOTST Atmospheric density profile 0= winter; 1= summer [0 or 1]
POR
[0 to 1]
TPFM Entry Modeling Results- Summary
• Modeled as either porous (P) or homogeneous (H) body
• Modeled as either a collective wake (CW) behavior or as
non-collective wake behavior (NCW)
• BEST FIT so far (End height fit and not a light curve fit):
• CW
 P = 70 %; 2 m diameter spherical;  = 2/3  Bolide
Group IIIA (Strong cometary material), but the
implied luminous efficiency compared to released
satellite data is ~100 % (However, our very well
calibrated differential luminous efficiency prediction
for this case is ~1 %).
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Entry modeling: Sphere;  = 2/3
2 m diameter 70 % porous chondritic asteroid
Inverse Entry Modeling Iterations
• Solution Search Parameters:
 1 km/s < V < 20 km/s (Higher velocities not applicable)
 0.01 m < R < 100 m (Larger and smaller sizes not applicable)
 Bolide groups searched: I (Ordinary chondrite), II
(Carbonaceous chondrite), IIIA (Strong cometary material),
IIIB (Weak cometary material)
 Nominal ablation parameters, , and bulk densities, m, for
each group (Ceplecha et al, 1997): Homogeneous meteor model,
Porosity limit = 0 %
 Number of fragments = 1 (Only the original body without
fragments).
 Wave drag coefficient, CD = 0.92, Spherical unchanging shape
 Isothermal, hydrostatic model atmosphere utilized
 Observed end height with a specified error bar
Inverse Entry Modeling Summary
Observed
Entry
velocity
Summary and Conclusions
• For the first time an astronomical object (in this case a small
asteroid or a large meteor-fireball) was observed with telescopes
prior to its entry into the atmosphere. The primary purpose of
such telescopic systems is to search for the potential “killer”
bolides that could end life on Earth as we now know it.
• Official U.S. Government satellite detection data announced
• Modeling using LANL entry modeling codes
 DIRECT: Consistent with a Group IIIA bolide (Strong
cometary material)
 INVERSE: Consistent with a Group IIIA or Group IIIB bolide
• Detected by the CTBT IMS (International Monitoring System)
infrasonic pressure wave arrays in Kenya and in Kazakhstan.
 Great circle bearing intersection confirms astronomical impact
location predictions.
 Great circle bearing intersection confirms event origin time.