Why Solar Electron Beams Stop Producing Type III Radio Emission Hamish Reid, Eduard Kontar SUPA School of Physics and Astronomy University of Glasgow, UK 0

1 Type III radio bursts are created by electrons and can be observed in space and/or at Earth (e.g. see Reid & Ratcliffe 2014 RAA). Type III Radio Bursts

2 FREQUENCY [MHZ] TIME Type III burst frequency (related to background electron density) decreases as a function of distance from the Sun.

3 Type III Radio Bursts

High Frequency Type IIIs Sometimes we observe type III bursts at high frequencies. What causes an abrupt stop of radio emission?

Work on the stopping frequency by LeBlanc et al 1995, 1996 using Ulysses and Wind Stopping Frequencies

What causes the electron beam to stop producing radio emission during its flight through the solar system? Properties of the electron beam? Properties of the background heliospheric plasma? Type III Stopping Frequency

One dimensional kinetic equations to simulate electron beam travel (see Reid and Kontar 2013 for equations). We include…. Quasilinear eqns model Langmuir wave-particle interactions. Coulomb collisions for particles and waves. Spontaneous emission of Langmuir waves. Langmuir wave refraction from plasma inhomogeneities. Radial magnetic flux rope expansion. Dont include radio for simplicity (Ratcliffe et al 2014 A&A acc.) Simulation Model

Magnetic Flux Rope Expansion SUN § § Acceleration Region

Magnetic Flux Rope Expansion SUN Acceleration Region § § Magnetic Field Expansion of R -1.5 R -2, R -2.5,..… R -β

Different Dynamic Spectra

Expansion vs. Stopping Freq.

Effects of Density Fluctuations Strong Weak

Initial Electron Beam Params. Starting frequency of type III bursts correlated with the spectral index of X-rays (Reid et al 2014). Correlation between spectral index of X-rays and in-situ measured electrons at 1 AU (Krucker et al. 2007).

Spectral Index

Beam Densities

Beam Density vs. Stop. Freq.

Increased Coronal Expansion SUN § § Acceleration Region Accelerated Electron Cloud Magnetic Field

Increased Coronal Expansion SUN § § Critical Height [r c ] Acceleration Region Accelerated Electron Cloud Magnetic Field

High Freq Dynamic Spectra Weak extra expansion

High Freq Dynamic Spectra Medium extra expansion

High Freq Dynamic Spectra Strong extra expansion

A number of parameters can affect stopping frequency Radial Expansion of the Magnetic Field – Diagnostic of magnetic field structure? Background Density Fluctuations. Electron Beam Parameters – Spectral Index, Density – Use X-rays to make prediction of type III behaviour? Increased radial expansion in the upper solar atmosphere my cause coronal type III bursts. Conclusion

Radial Expansion As the magnetic field expands the electron cloud rarefies. We model the radial expansion by using where β determines the rate of radial expansion and r 0 determines the base of the conical expansion. The base, r 0 =3.5x10 9 cm and makes a cone of 33 0 when β=2. We modify the radial expansion of the magnetic field to expand at different rates. β=2, 2.5, 3, 3.5

We use the Langmuir wave energy density as a proxy for the radio emission of type IIIs. The initial level of Langmuir wave spectral energy denisty is defined as: To obtain the energy density we integrate the spectral energy density over k: Radial Expansion

Distribution function varies with velocity as a power-law Distribution function varies as a Gaussian in position space Distribution function varies as a Gaussian in time with different rise and decay times Beam Initial Conditions

Density Model The background density model remains static in time due to the high energy electrons moving much faster. We use the Parker 1958 density model with normalisation constant from Mann et al 1999.

One dimensional quasilinear equations describing the kinetics of energetic electrons and Langmuir waves (e.g. Reid and Kontar 2013). Wave Generation and Absorption Background Plasma Inhomogeneity Collisions Spontaneous Emissions One Dimensional QL equations Radial Propagation and Expansion

Radial Expansion

Density Fluctuations

Beam Density

We include density fluctuations into the code such that: Where Δn/n = 0.1 at 1 AU. We also vary them as a function of distance (Reid & Kontar 2010) such that: We use a value of Ψ=0.25. Density Fluctuations

In the presence of density fluctuations, we observe the beam travels a shorter distance before type III emission would be suppressed. How does this change if we alter the level of density fluctuations? We change Ψ=0.25, 0.5, 0.75 and no perturbations. Density Fluctuations

We modify the initial expansion function M(r) such that it includes a critical height r c for extra expansion. Setting r 0 =10 10 cm and β=3 we alter the value of A and r c such that we have a varying level of increased expansion at different heights. Coronal Type IIIs

Radial Expansion – Stop. Freq.