1. Stanford Wave Induced Particle Precipitation (WIPP) Code Prajwal Kulkarni U.S. Inan, T.F. Bell March 4, 2008 Space, Telecommunications and Radioscience (STAR) Laboratory Stanford University Stanford, CA

2. 2 Outline 1.Motivation 2.Ground-based VLF Transmitters 3.Wave-Particle Interaction 4.Simulation Results 5.Conclusions

3. 3 Motivation and Procedure  Resonant interactions with waves are responsible for the acceleration and loss of radiation belt electrons.  In the inner belt and slot region, different types of waves (whistlers, hiss, VLF transmitters) are important drivers of precipitation.  Abel and Thorne [1998a]  Inan et al. [1984] used a test particle approach to calculate precipitation zones around existing ground-based VLF transmitters  Considered only ducted propagation  We calculate the precipitation signatures induced by the NPM, NWC, NLK, NAU and NAA ground-based VLF transmitters as well as by hypothetical transmitters  Utilize the Stanford 2D VLF Raytracing program  Calculate Landau damping along raypath [Bell et al., 2002].  Calculate energetic electron precipitation based on method of Bortnik et al. [2005a, 2005b].  We focus on > 100 keV electrons

4. 4 Transmitter Parameters L = 2.75 f = 24.8 kHz 192 kW L = 1.15 f = 21.4 kHz 424 kW L = 2.98 f = 24.0 kHz 1000 kW L = 1.38 f = 19.8 kHz 1000 kW L = 1.30 f = 40.75 kHz 100 kW

5. 5 21.4 kHz 424 kW L = 1.15 21.4° VLF Transmitters

6. 6 No Magnetospheric Reflections  Wave frequency must be below the local lower hybrid resonance frequency, f LHR  f LHR generally below 13 kHz in inner magnetosphere  Increases at locations closer to the surface of the earth.  Ground based transmitters radiate frequencies above the f LHR and therefore do not MR

7. 7 Wave-Particle Interaction  H effectively determines electron resonant velocity Higher frequency waves resonate with lower energy electrons So which factor is most important: location, frequency, radiated power?  H : gyrofrequency  : wave frequency k z : wave k-vector  : relativistic gamma-factor v z : resonant electron velocity

8. 8 Case Study NAA: L = 2.98 (54.6 o ), 24.00 kHz, 1 MW NAU: L = 1.30 (28.6 o ), 40.75 kHz, 100 kW Both at 100 kW, NAA location, equatorial interactions Actual locations, 100 kW Off-equatorial interactions Actual characteristics Both at 100 kW Equatorial Interactions

9. 9

10. 10 Role of Source Location

11. 11 Role of Source Location: 100 keV All transmitters at 1 MW radiated power

12. 12 Role of Source Location: 1 MeV All transmitters at 1 MW radiated power

13. 13 Role of Radiated Power

14. 14 Underlying Models

15. 15 Conclusion  We have calculated > 100 keV energetic electron precipitation signatures that would be induced by five existing ground-based VLF transmitters  NAA, NLK, NAU, NPM, NWC  NWC induces the strongest precipitation signature  Simulated several hypothetical transmitters distributed broadly in geomagnetic latitude and operating at a wide range of frequencies.  Investigated the relationship between transmitter location, operating frequency and radiated power   H (source location) directly proportional to resonant energy   inversely proportional to resonant energy  Location, location, location!  Future work: compare predictions with data