Stanford Wave Induced Particle Precipitation (WIPP) Code

Stanford Wave Induced Particle Precipitation (WIPP) Code

Prajwal KulkarniU.S. Inan, T.F. Bell

March 4, 2008

Space, Telecommunications and Radioscience (STAR) Laboratory

Stanford UniversityStanford, CA

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Outline

1. Motivation

2. Ground-based VLF Transmitters

3. Wave-Particle Interaction

4. Simulation Results

5. Conclusions

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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

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Transmitter Parameters

L = 2.75f = 24.8 kHz192 kW

L = 1.15f = 21.4 kHz424 kW

L = 2.98f = 24.0 kHz1000 kW

L = 1.38f = 19.8 kHz1000 kW

L = 1.30f = 40.75 kHz100 kW

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21.4 kHz 424 kW L = 1.15 21.4°

VLF Transmitters

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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 fLHR and therefore do not MR

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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 frequencykz: wave k-vector: relativistic gamma-factorvz: resonant electron velocity

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Case Study

NAA: L = 2.98 (54.6o), 24.00 kHz, 1 MW NAU: L = 1.30 (28.6o), 40.75 kHz, 100 kW

Both at 100 kW, NAA location, equatorial interactions

Actual locations, 100 kWOff-equatorial interactions

Actual characteristicsBoth at 100 kWEquatorial Interactions

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Role of Source Location

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Role of Source Location: 100 keV

All transmitters at 1 MW radiated power

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Role of Source Location: 1 MeV

All transmitters at 1 MW radiated power

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Role of Radiated Power

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Underlying Models

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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