Atmospheric Chemistry

1. Atmospheric Chemistry Prepared by Benjamin Cotts Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global AWESOME Network

2. Overview • LEP Events • Early/fast Events • Gamma Ray Burst (GRB) Events • Atmospheric Chemistry

3. LEP Event Properties Onset delay (∆t ~ 0.5-2 s) between sferic and onset Differential onset delay with respect to L-shell (~0.5s) Onset duration (td ~ 1-2 s) of secondary ionization Large ionospheric region of disturbance, ~ 2000 km Occur very frequently Recovery typically ~ 10-100 s

4. Recovery Signatures of LEP Peter 2007 Pasko and Inan, 1994

5. Early VLF Event Properties • Rapid onset delay (Dt < 20 ms) • Rapid onset duration (td < 20 ms) • Typically recover in ~30-200 s • Event amplitudes ~0.2-0.8 dB, rarely >1 dB • Causative CGs <50 km from perturbed path • Lateral extent of disturbances ~100 km Source: [Johnson and Inan 1999]

6. Long Recovery Early/fast Events

7. Gamma-Ray Bursts • Associated with very energetic explosions • Collision of Neutron stars • Magnetar • Typically lasts a few ms to several minutes • Accidentally discovered by Vela-3 spacecraft in 1967

8. Massive Gamma-Ray Burst From Inan et al. 2007

9. Second Timescale Characteristics -25 dB disturbance!! From Inan et al. 2007 From Inan et al. 2007

10. Hour Timescale Characteristic Recovery lasts for over 1 hour! From Inan et al. 2007

11. Overview • Ionospheric chemistry • Model Framework • Constituents/Parameters

12. Chemistry Model: Species • Ne - Electrons • N+ - Light positive ions • Nx+ - Heavy positive ions (cluster) • N- - Light negative ions • Nx- - Heavy negative ions (cluster) Not part of the model, just illustrative:

13. b - attachment: g - detachment from light negative ions gx - detachment from heavy negative ions ai - mutual neutralization ad, adc- dissociative recombination A - rate of conversion N -Nx- B- rate of conversion N+Nx+

14. 5 constituents: Ne - electrons N+ - light positive ions O2+, NO2+, N2+, … Nx+ - positive ion clusters H+(H2O)n N- - light negative ions O-, O2-, … Nx- - heavy negative ions NO3-, NO3-(H2O)n Coefficients: ai - mutual neutralization ad, adc - dissociative recombination b - attachment: 3-body and 2-body (in E) g - detachment from light negative ions (value uncertain): Electron affinity=0.4 eV  highly dependent on T During daytime: photodetachment=0.4 s-1 Also due to active species, Nac: O, N, O2(a1Dg) gx - detachment from heavy negative ions, approximately=0 (electron affinity = 3.91 eV), photodetachment = 0.002 s-1 (during daytime) B - rate of conversion N+Nx+ A - rate of conversion N -Nx- Q – Ionization source; Cosmic ray only source at low altitudes Qcr (peaks at ~15 km) Model of Ionospheric Chemistry

15. Inan et al., 2007 • Relaxation matches model results, 2 stages: • Free electrons are quickly attached, t1 ~ (g+b)-1 • Positive and negative ions recombine, t2 ~ (aiNi)-1 ~ 104 s • Recall Gamma-Ray Burst

16. Gamma-Ray Burst • Ionization profile recovery

18. Bibliography • Mitra, A. P. 1975 • Ferguson, 1979 • Arijs, 1992 • Glukhov et al., 1992 • Pasko and Inan, 1994 • Rodger et al., 1998 • Inan et al., 2007 • Lehtinen and Inan, 2007