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Understanding Wave-Induced Particle Precipitation with Stanford WIPP Code

Explore how ground-based VLF transmitters drive electron precipitation using the Stanford WIPP Code. Study resonant wave-particle interactions and simulation results to understand energetic electron behaviors. Investigate the impact of location, frequency, and radiated power on precipitation signatures.

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Understanding Wave-Induced Particle Precipitation with Stanford WIPP Code

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  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. Outline • Motivation • Ground-based VLF Transmitters • Wave-Particle Interaction • Simulation Results • Conclusions

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

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

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

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

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

  9. Role of Source Location

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

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

  12. Role of Radiated Power

  13. Underlying Models

  14. 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

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