Theoretical study of ELF/VLF wave generation by HAARP

1. Theoretical study of ELF/VLF wave generation by HAARP Nikolai G. Lehtinen Stanford December 4, 2005

2. Generation of ELF/VLF waves

3. HAARP High Frequency Active Auroral Research Program After upgrade in March 2006: • 180 crossed dipole antennas • 3.6 MW power • ~2 GW effective radiated HF power (2.8-10 MHz) (lightning has ~20 GW isotropic ERP)

4. HAARP and other HF heating facilities

5. Important electron-molecule interaction concept: Dynamic friction force Inelastic processes: • Rotational, vibrational, electronic level excitations • Dissociative losses • Ionization (E/N)br=130 Td where 1 Td = 10-21 V-m2

6. Time-dependent solution for f(v,t) = f0(v,t) + cosq f1(v,t) (almost isotropic) Physical processes inluded in ELENDIF: Quasistatic electric field Elastic scattering on neutrals and ions Inelastic and superelastic scattering Electron-electron collisions Attachment and ionization Photon-electron processes External source of electrons New: Non-static (harmonic) electric field Geomagnetic field Kinetic Equation Solver(modified ELENDIF)

7. Importance of these processes • The quasistatic approximation used by ELENDIF requires nm>>w • Geomagnetic field is also important: wH~2p x 1 MHz wH wHAARP

8. Analytical solution • Margenau distribution where l=v/nm=(Nsm)-1=const • Druyvesteyn distribution w=0

9. Calculated electron distributions Electron distributions for various RMS E/N (in Td). f>0 corresponds to extaordinary wave (fH=1 MHz, h=91 km) • Effective electric field is smaller than in DC case: + ordinary - extraordinary

10. Breakdown field(used for the estimate of nm,eff) h = 91 km, extraordinary, fH=1 MHz • Breakdown occurs when nion>natt • The point of breakdown (shown with ) shifts up in oscillating field • f(v) at ionization energy (~15 eV) is most important

11. HF wave propagation • Power flux (1D), including losses: • HF conductivity (ordinary/extaordinary)

12. Calculated HF electric field • For comparison, we show the dynamic friction function. • Current and upgraded HAARP power are both shown.

13. Temperature modification(daytime, x mode)

14. Comparison of Maxwellian andnon-Maxwellian approaches

15. Electrojet current modulation • Conductivity changes due to modification of electron distribution • Previous models: DE=0 (inaccurate at low frequencies) • This model: static fields, div J=0

16. Conductivity tensor (DC) • Approximate formulas were used before • Pedersen (transverse) • Hall (off-diagonal) • Parallel

17. Conductivity modification • Pedersen conductivity is increased • Parallel conductivity is decreased

18. 3D stationary DJ • Vertical B • Ambient E is along x • Ambient current is mostly along y • Models with DE=0 do not consider closing side currents • max DJ/J0~0.3 for this case

19. Calculated DJ/J0 for various frequencies • Range 70-130 km • Calculated maximum current and its modification occur at 109 km

20. Conclusions • Maxwellian electron distribution models, which calculate DTe, cannot account for the nonlinear Te saturation. • The non-Maxwellian model allows to calculate optical emissions and breakdown processes. • We are working on a creation of a universal modelling tool for ionosphere heating, which will calculate ELF/VLF emission on ground level and in space.

21. Work in progress • Current changes in non-static case • ELF/VLF emission • ELF/VLF wave propagation along the geomagnetic field line