High resolution kilometric range optical telemetry in air ...
Astrophysics Seminar October 2004 R. L. Mutel (& D. Menietti) University of Iowa Fine Structure in...
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Transcript of Astrophysics Seminar October 2004 R. L. Mutel (& D. Menietti) University of Iowa Fine Structure in...
Astrophysics Seminar
October 2004
R. L. Mutel (& D. Menietti)
University of Iowa
Fine Structure in Auroral Kilometric Radiation: Evidence for
Electromagnetic and Electrostatic Ion Cyclotron Waves
UI Space/Astro Seminar October 2004
Earth as a radio source
UI Space/Astro Seminar October 2004
AKR is generated 6000-12000 km above the visible aurora
AKR is generated at f = ωce
by electron cyclotron maser
UI Space/Astro Seminar October 2004
Dynamic Spectra of Common AKR Bursts
Geotail
Cluster
UI Space/Astro Seminar October 2004
May 15 AKR Event: Variation with Magnetic Latitude
m = -53°
m = -38°
m = -32°
UI Space/Astro Seminar October 2004
Example of WBD Dynamic Spectra
(250-262 KHz, 30 sec), S/C separation ~300 km
Auroral Kilometric Radiation (AKR) Bursts
Auroral Kilometric Radiation (AKR) Bursts
Spacecraft
1
3
4
UI Space/Astro Seminar October 2004
FAST Observations of AKR Source Region (Ergun et al. Ap. J. 538, 456)
Note e- depletion in auroral cavity
Note e- depletion in auroral cavity
UI Space/Astro Seminar October 2004
FAST Observations of AKR Source Region (Ergun et al. Ap. J. 538, 456)
Shell instabilityShell instability
UI Space/Astro Seminar October 2004
University of Iowa Wideband Data Plasma Wave Instrument (WBD)
• Identical WBD instruments are mounted on all four spacecraft. Single dipole antenna used.
• Real-time downlink of 220 kb/s to the NASA Deep Space Network (DSN). (One DSN antenna per S/C!)
• DSN provides real-time time stamps (accuracy 10 s).
• AKR studies use 125, 250, and 500 KHz bands, 10 KHZ bandwidth, 37 s sampling time.
• High frequency/time resolution capability of WBD is the primary characteristic that makes WBD unique from the other Cluster wave experiments, which operate at much lower data rates.
UI Space/Astro Seminar October 2004
VLBI Source Location Algorithm: Differential delay measurement
UI Space/Astro Seminar October 2004
Sample Dynamic Spectrum, Waveform and Cross-correlation
Waveforms from each Cluster WBD receiver for AKR burst shown
at leftPeak is fit with Gaussian, delay uncertainty ~ 0.3 ms
UI Space/Astro Seminar October 2004
• A uniform 3-d grid of points is constructed centered on the Earth with spacing 0.1 Re and dimension 8 Re on each side (512,000 pts).
• The propagation time to each satellite is computed from each grid point.
• Differential delays are then computed for each baseline and compared with the observed delays, as measured by cross-correlating the waveforms from each pair of spacecraft
AKR Burst Position search algorithm
UI Space/Astro Seminar October 2004
VLBI position uncertainty calculation
1 12 22 2
2 21
2 2
B Bz x z x
c
500z
x c kmB
2
2 5,000z
x c kmB
Delay uncertainties in plane and parallel to line of sight:
Typical uncertainty in plane:
Typical uncertainty in plane:x
UI Space/Astro Seminar October 2004
Uncertainty mapped to Earth (CGM coordinates)
Uncertainty ~ 500 km -1000 km
Uncertainty ~ 200 km -400 km
UI Space/Astro Seminar October 2004
Refractive effects
effect on AKR burst location determination
unimportant for S/C magnetic latitudes > 40°
(plasmasphere model
Gallagher et al.2000)
UI Space/Astro Seminar October 2004
Refractive Ray tracing corrections
UI Space/Astro Seminar October 2004
AKR Bursts: Locus of Allowed Locations
Locus of allowed locations for AKR burst on 10 July 2002 at 08:47:02 and illustrated at right.
The top panels show the unconstrained solution of all allowed points (left is oblique view; right view is from spacecraft).
The lower panel shows the constrained solution assuming the AKR emission arises from a radius distance from Earth consistent with the observed frequency being identified with the electron gyrofrequency. A model auroral oval is shown for reference.
UI Space/Astro Seminar October 2004
AKR Burst Locations: The movie
UI Space/Astro Seminar October 2004
Summary of 4 Spacecraft VLBI Epochs (Fully Analyzed)Southern Hemisphere Observations
Northern Hemisphere Observations
Epoch N /S S/C DOY UT N MLT Comments
20jul02 N 43/28 02-201 13.0-15.0 34 -4.5 62.7 Very spread in inv. Lat.
28oct02 N 32 02-301 10.6-11.1 150 -2.3 63.8 Well defined 09nov02 N 54/34 02-313 6.5-8.4 568 -3.3 68.4 Beautiful, well
defined 14nov02 N 19 02-318 7.0-8.5 130 2.6 74.8 Well defined 15dec02 N 34 02-349 3.4-3.7 22 1.7 70.6 22dec02 N 34 02-356 4.4-4.7 277 -0.3 68.0 29dec02 N 47 02-363 5.0-6.5 221 -4.7 70.2 Well defined 22jan03 N 52/34 03-022 0.9-2.7 372 -6.8 71.3 Temporal
migration Total/average 9 1774 -2.2 68.7
Epoch N /S S/C DOY UT N MLT Comments 20jun 02 S -25/-35 02-171 16.1-16.2 56 -8.5 -75.5 Well defined 05jul02 S -55 02-186 11.6-12.4 84 1.3 -70.5 Along line 10jul02 S -55/-70 02-191 8.2-10.0 319 0.8 -75.1 Well defined 17jul02 S -45/-60 02-198 10.6-11.9 81 2.1 -71.7 Along line, mostly
A zone 10aug02 S -60/-73 02-222 7.4-8.5 83 -1.0 -70.6 Very elongated
along line 19aug02 S -66/-76 02-231 17.2-19.5 171 -1.3 -75.0 31aug02 S -70/-80 02-243 16.0-19.5 242 -1.6 -77.8 26sep02 S -62 02-269 18.1-18.9 34 -2.6 -74.3
Total/average 9 1070 -1.35 -73.8
UI Space/Astro Seminar October 2004
November 9 Locations: Varying Perspectives (Animation)
UI Space/Astro Seminar October 2004
Nov 9 :The Movie Mapped onto CGM coordinates
UI Space/Astro Seminar October 2004
Observed distribution of AKR bursts
UI Space/Astro Seminar October 2004
AKR Burst locations
vs.
UI Space/Astro Seminar October 2004
Example of position uncertainty including
depth-of-field(9 Oct 02)
Blue: fgyro – 10%
Red: fgyro + 10%
UI Space/Astro Seminar October 2004
Example of AKR Burst location with
Uncertainties projected into
100km Altitude, CGM coordinates
(29 Dec 02)
UI Space/Astro Seminar October 2004
Polar Average Images of Northern Auroral by month (Liou et al. 1997)
Evening Peak ~22h MLT April -May
Day peak at ~15h MLT June -July
UI Space/Astro Seminar October 2004
Summary of 4 Spacecraft VLBI Epochs (Fully Analyzed)Southern Hemisphere Observations
Northern Hemisphere Observations
Epoch N /S S/C DOY UT N MLT Comments
20jul02 N 43/28 02-201 13.0-15.0 34 -4.5 62.7 Very spread in inv. Lat.
28oct02 N 32 02-301 10.6-11.1 150 -2.3 63.8 Well defined 09nov02 N 54/34 02-313 6.5-8.4 568 -3.3 68.4 Beautiful, well
defined 14nov02 N 19 02-318 7.0-8.5 130 2.6 74.8 Well defined 15dec02 N 34 02-349 3.4-3.7 22 1.7 70.6 22dec02 N 34 02-356 4.4-4.7 277 -0.3 68.0 29dec02 N 47 02-363 5.0-6.5 221 -4.7 70.2 Well defined 22jan03 N 52/34 03-022 0.9-2.7 372 -6.8 71.3 Temporal
migration Total/average 9 1774 -2.2 68.7
Epoch N /S S/C DOY UT N MLT Comments 20jun 02 S -25/-35 02-171 16.1-16.2 56 -8.5 -75.5 Well defined 05jul02 S -55 02-186 11.6-12.4 84 1.3 -70.5 Along line 10jul02 S -55/-70 02-191 8.2-10.0 319 0.8 -75.1 Well defined 17jul02 S -45/-60 02-198 10.6-11.9 81 2.1 -71.7 Along line, mostly
A zone 10aug02 S -60/-73 02-222 7.4-8.5 83 -1.0 -70.6 Very elongated
along line 19aug02 S -66/-76 02-231 17.2-19.5 171 -1.3 -75.0 31aug02 S -70/-80 02-243 16.0-19.5 242 -1.6 -77.8 26sep02 S -62 02-269 18.1-18.9 34 -2.6 -74.3
Total/average 9 1070 -1.35 -73.8
UI Space/Astro Seminar October 2004
Histogram of AKR Burst Locations
CGM coordinates, 5 epochs Southern hemisphere only
UI Space/Astro Seminar October 2004
November 9 Locations: Varying Perspectives (Animation)
UI Space/Astro Seminar October 2004
Nov 9 :The Movie Mapped onto CGM coordinates
UI Space/Astro Seminar October 2004
Observed distribution of AKR bursts
UI Space/Astro Seminar October 2004
AKR Burst locations
vs.
UI Space/Astro Seminar October 2004
Example of position uncertainty including
depth-of-field(9 Oct 02)
Blue: fgyro – 10%
Red: fgyro + 10%
UI Space/Astro Seminar October 2004
Example of AKR Burst location with
Uncertainties projected into
100km Altitude, CGM coordinates
(29 Dec 02)
UI Space/Astro Seminar October 2004
Polar Average Images of Northern Auroral by month (Liou et al. 1997)
Evening Peak ~22h MLT April -May
Day peak at ~15h MLT June -July
UI Space/Astro Seminar October 2004
UI Space/Astro Seminar October 2004
AKR burst mean location drift: example119 Aug 2002,
Southern hemisphere
UI Space/Astro Seminar October 2004
AKR burst mean location drift: example222 Jan 2003, N hemisphere
UI Space/Astro Seminar October 2004
First simultaneous AKR/VLBI location map with UV image (IMAGE). June 8 , 2004
AKR burst is associated with discrete auroral
arc
UI Space/Astro Seminar October 2004
‘Rain’ AKR bursts: Narrow, rapidly drifting structures
“normal” AKR burst
“Rain” AKR bursts
UI Space/Astro Seminar October 2004
AKR Dynamic Spectrum 125 KHz17 July 2002 11:42:30 – 11:43:00
Slope -8.7 KHz/sec
UI Space/Astro Seminar October 2004
AKR Dynamic Spectrum 125 KHz17 July 2002 11:42:30 – 11:43:00
Slope = -3.1 KHz/sec
UI Space/Astro Seminar October 2004
Rain AKR bursts at 125 KHz31Aug 2002 16:14:30-16:15:00 UT
Modulated periodic structures
Slope -6.3 KHz/sec
UI Space/Astro Seminar October 2004
Rain AKR bursts at 500 KHz31Aug 2002 19:26:00- 19:26:30 UT
Slope -12.5 KHz/sec
UI Space/Astro Seminar October 2004
Derived Speed compared with Alfven, and Electron, Ion Acoustic speeds versus Radial distance (assumes 0.1-10
keV particles)
Ion acoustic speed
Electron acoustic speed
Alfven speed
500 KHz 250 KHz 125 KHz
UI Space/Astro Seminar October 2004
Derived Exciter speed along B field
125 KHz
500 KHz
UI Space/Astro Seminar October 2004
Exitor speed derived from frequency drift
3
43 erdf df dr df
V Vdt dr dt dr r
2
3
0
e oobs
obs
r fdfV f
f dt f
3
0 1.66eobs o
rf f f MHz
r
2. Use (negative) frequency drift to derive (upward) wave speed
1. Assume EM at electron gyro-frequency, dipolar magnetic field
3. Recast in terms of fobs
4. Amplitude modulation conversion to spatial wavelength
3 25 /obsfdfHz km
dt r
UI Space/Astro Seminar October 2004
Striated AKR from 0-120 KHz(Menietti et al. 2000)
Slope ~ 1 KHz/sec @100 KHz
Slope ~ 0.5 KHz/sec @40 KHz
UI Space/Astro Seminar October 2004
UI Space/Astro Seminar October 2004
Modulation of Striated AKR: Is it due to Faraday rotation?
2e
L
c n B dl
Requires:
• Linearly polarized emission (but AKR is circularly polarized)
• Δ ≈ 3 turns/KHz @ 125 KHz (λ=2.4 km) =>
RM = 10-3 rad-m-2
• This may be plausible: B ~ 0.1 gauss, ne ~ 10 cm-3, L ~ 100 km
UI Space/Astro Seminar October 2004
UI Space/Astro Seminar October 2004
Sampled at 1024 channels
UI Space/Astro Seminar October 2004
Sampled at 2048 channels
UI Space/Astro Seminar October 2004
Wavelet dynamic spectrum of Striated bursts, 2 spacecraft
correlation
UI Space/Astro Seminar October 2004
Electromagnetic Ion-Cyclotron Wave Group Speed vs. Frequency
2
22
2 ci
pe cicipi
ci pi ce
cNd
dk
12 2 2
pi pe
ci ce
N
where
Note: Plot assumes
• Dipolar B field
•Ne (r) ~ r -3.2 (Persoon model)
UI Space/Astro Seminar October 2004
Banded Modulation of AKR: Evidence for Electrostatic Ion Cyclotron (EIC) Waves?
UI Space/Astro Seminar October 2004
Close-up of AKR banded modulation
140ci Hz
Separation = 120 ± 5 Hz
UI Space/Astro Seminar October 2004
UI Space/Astro Seminar October 2004
2
UI Space/Astro Seminar October 2004
What excites rain AKR? Model assumptions
• Observed emission is same as ‘normal’ AKR: electron cyclotron maser near electron cyclotron frequency
• Earth’s magnetic field is strictly dipolar (OK for r < 2.5 Re)
• A disturbance traveling parallel to B stimulates EM emission
• Observed slope indicates phase speed of wave along B field
• Observed banded modulation may indicates characteristic wavelength of exciter (after conversion to spatial separation)