Space Environment and Satellite Systems Plasma Turbulence of Non-Specular Trail Plasmas as Measured by a High Power Large Aperture Radar Jonathan Yee and Sigrid Close Stanford University January 9, 2013
Outline Meteoroid Diffusion - Introduction to Meteor Trails Motivation Formation Detection - Turbulence Onset Times - Ambipolar Diffusion Coefficient - Trail Diffusion Shape - Parallel and Perpendicular Variations to the Magnetic Field Image Courtesy of Universe Today, 2010 2
Motivation Understand plasma expansion in a collisional environment Better understanding of the ionosphere through small perturbations to the background plasma Extend to the expansion of plasma in space created from a meteoroid strike on a satellite Verify trail diffusion simulations with radar data results Courtesy of Dyrud et al., 2001 3
Formation of Meteoroid Trails Meteoroids heat up and ablate in Earth s atmosphere neutral air molecules Collisions ionize neutral air molecules Produces plasma regions Head region directly surrounding meteoroid Trails region left behind meteoroid 4
Formation of Meteoroid Trails Meteoroids heat up and ablate in Earth s atmosphere Ionized Particles Collisions ionize neutral air molecules Produces plasma regions Head region directly surrounding meteoroid Trails region left behind meteoroid Hot Meteoroid 5
Formation of Meteoroid Trails Meteoroids heat up and ablate in Earth s atmosphere Ionized Particles Collisions ionize neutral air molecules Produces plasma regions Head region directly surrounding meteoroid Trails region left behind meteoroid Trails Heads Hot Meteoroid 6
Dual Frequency VHF (160 MHz) UHF (422 MHz) ALTAIR System High Resolution Dual Circular Polarization Monopulse Angles 7
Dual Frequency VHF (160 MHz) UHF (422 MHz) ALTAIR System Beam Center E-Region 140 km High Resolution Dual Circular Polarization 70 km Monopulse Angles Hot Meteoroid Data Set 2007 year long collect 100,000+ head echoes TBD nonspecular trails 8
Polarization and Frequency Transmit in RC and expect return to be LC, but both LC and RC returns are detected Three possible explanations Modification of the RF wave due to wave frequency, plasma layer width, collision frequency, or electron density Geometric changes, such as multiple scatters from meteoroid fragmentation or asymmetry in the trail shape Striations in the trails UHF and VHF SNR depend on wavelength raised to ~6 9
Altitude (km) Power (db) Altitude (km) Power (db) Meteor Trail Case Studies 50 50 102 102 100 45 100 45 98 40 98 40 96 35 96 35 94 30 94 30 92 25 92 25 90 20 90 20 88 19 20 21 22 23 Time (sec) 15 88 19 20 21 22 23 Time (sec) 15 Left Circular Return Nov. 18, 2007 6 AM Right Circular Return Nov. 18, 2007 6 AM 10
Altitude (km) Power (db) Altitude (km) Power (db) Meteor Trail Case Studies 108 VHF Detection Jan. 6, 2007 5 AM 50 108 UHF Detection Jan. 6, 2007 5 AM 50 107 106 105 45 40 107 106 105 Non-Specular Trail 45 40 104 103 35 104 103 35 102 30 102 30 101 100 99 25 20 101 100 99 Head Echo 25 20 98 41 41.5 42 Time (sec) 15 98 41 41.5 42 Time (sec) 15 11
Altitude (km) Altitude (km) Turbulence Onset: Results Average over 152 nonspecular trails 115 110 105 Average Time Delay vs. Altitude Average Time Delay 25 ms Delay 40 ms Delay 115 110 105 Average Time Delay For Signal Return Type Average Time Delay (LC) Average Time Delay (RC) Average Time Delay (LC + RC) 25 ms Delay 40 ms Delay 100 100 95 95 90 90 85 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Average Time Delay (sec) 85 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Average Time Delay (sec) 12
Altitude (km) Altitude (km) Turbulence Onset: Results Average over 108 VHF and 43 UHF nonspecular trails 115 110 105 Average Time Delay for VHF Trails Average Time Delay (LC) Average Time Delay (RC) Average Time Delay (LC + RC) 25 ms Delay 40 ms Delay 115 110 105 Average Time Delay for UHF Trails Average Time Delay (LC) Average Time Delay (RC) Average Time Delay (LC + RC) 25 ms Delay 40 ms Delay 100 100 95 95 90 90 85 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Average Time Delay (sec) 85 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Average Time Delay (sec) 13
Ambipolar Diffusion Coefficient Assumptions Weakly ionized Collisional frequency is large Accounts for the diffusion of both ions and electrons in a plasma via an electric field In the presence of a magnetic field, the electrons would simply move along the field lines Ambipolar Diffusion Coefficient: D a = μ ed i + μ i D e μ i + μ e D = KT mν From a radar signal: τ = λ 2 16 π 2 D a μ = q mν (Greenhow et al., 1955) 14
LC SNR (db) Diffusion Coefficient: Calculation Fit a line to SNR vs. time for a given altitude Calculated for each altitude when SNR is 1/e of initial value 50 40 30 20 10 0-10 LC SNR vs. Time -20 0.2 0.4 0.6 0.8 1 Time (sec) 15
Altitude [km] Altitude [km] Diffusion Coefficient: Results Averaged Diffusion Coefficient Weighted Averaged Diffusion Coefficient 110 Model LC RC LC + RC 110 Model LC RC LC + RC 105 105 100 100 95 95 90 90 10-3 10-2 10-1 10 0 10 1 Diffusion Coefficient [m 2 /s] 10-5 10-4 10-3 10-2 10-1 10 0 10 1 Diffusion Coefficient [m 2 /s] Model: h = 4.43 log D a + 87.9 Shaded areas around data signify error bars Courtesy of Galligan et al., 2002 16
Altitude [km] Altitude [km] Diffusion Coefficient: Results VHF Weighted Averaged Diffusion Coefficient UHF Weighted Averaged Diffusion Coefficient 110 Model VHF LC VHF RC VHF (LC + RC) 110 Model UHF LC UHF RC UHF (LC + RC) 105 105 100 100 95 95 90 90 10-5 10-4 10-3 10-2 10-1 10 0 10 1 Diffusion Coefficient [m 2 /s] 10-5 10-4 10-3 10-2 10-1 10 0 10 1 Diffusion Coefficient [m 2 /s] Model: h = 4.43 log D a + 87.9 Shaded areas around data signify error bars Courtesy of Galligan et al., 2002 17
LC (db) Diffusion Shape: Results 2007-doy002-1800-VHF-10001to11000-16 3D-LC 70 104 102 60 100 98 50 96 94 40 92 5 30 0 0 5 20 Y (km) -5-5 X (km) 18
Diffusion Shape: Results 19
Y (km) LC (db) Diffusion Shape: New Axis Centered at the middle point of the head echo Rotated such that x-axis is parallel with the magnetic field 2007-doy002-1800-VHF-10001to11000-16 2D-LC 5 4 3 2 1 0-1 -2-3 70 60 50 40 30-4 -5-5 0 5 X (km) 20 20
Parallel Variance (km) Perpendicular Variance (km) Parallel Variance (km) Perpendicular Variance (km) Parallel & Perpendicular Variation 2007-doy006-1700-VHF-5001to6000-11: Parallel Variance 2007-doy006-1700-VHF-5001to6000-11: Perpendicular Variance 1 0.65 0.6 0.95 0.55 0.9 0.5 0.85 0.45 0.8 48.5 49 49.5 50 50.5 51 51.5 Time (sec) 1.1 1 0.9 0.8 Jan. 5, 2007 5 AM Parallel Variation Jan. 6, 2007 5 AM Parallel Variation 2007-doy005-1700-VHF-4001to5000-3: Parallel Variance 0.4 0.35 48.5 49 49.5 50 50.5 51 51.5 Time (sec) 1 0.9 0.8 Jan. 5, 2007 5 AM Perpendicular Variation Jan. 6, 2007 5 AM Perpendicular Variation 2007-doy005-1700-VHF-4001to5000-3: Perpendicular Variance 0.7 0.7 0.6 0.5 0.6 0.4 37 37.5 38 38.5 39 39.5 40 40.5 41 Time (sec) 0.5 37 37.5 38 38.5 39 39.5 40 40.5 41 Time (sec) 21
Fitted Slopes (km/sec) Fitted Slopes (km/sec) Weighted Slopes Parallel & Perpendicular Variation 10 9 8 Weighted Slopes for Parallel to Magnetic Field Line 10 9 8 Weighted Slopes for Perpendicular to Magnetic Field Line 7 7 6 6 5 5 4 4 3 3 2 2 1 1 0 0-1 0 50 100 150 Trail Numbers -1 0 50 100 150 Trail Numbers 22
Change in Standard Deviation Parallel & Perpendicular Variation Weighted Change in Standard Deviation 1.5 Parallel Perpendicular 1 0.5 0-0.5 0 50 100 150 Trails 23
Conclusion From the turbulence onset times: - There is large agreement with previous simulations with the large increase in onset times at lower altitudes possibly indicating ambient conditions From the ambipolar diffusion coefficient: - There is agreement in the upward trend with previous studies, but the order of magnitude is not in agreement From the diffusion structure: - There is evidence that the plasma is expanding in several directions (meteoroid direction and perpendicular/parallel to magnetic field) and is not in agreement with some of the assumptions made for ambipolar diffusion. Ambipolar Diffusion Coefficient is not sufficient to explain the diffusion process that occurs when meteoroids ablate in the ionosphere 24
Future Work Develop method for including both directions in calculations of the diffusion process for nonspecular trails Examine changing diffusion shape of nonspecular trails Explore the effects of polarization on plasma scattering 25
QUESTIONS? 26