Alexander Russell – Publications

List
  1. "Solar Active Region Flux Fragmentation, Subphotospheric Flows, and Flaring,"
    Canfield, R. C. and Russell, A. J. B.
    ApJ, Volume 662, Issue 1, pp. L39-L42, 2007.
    5 citations.

  2. “Resonant Absorption With 2D Variation of Field Line Eigenfrequencies,”
    Russell, A. J. B. and Wright, A. N.
    A&A, accepted, 2009.

  3. “Self-Consistent Ionospheric Density Modifications by Field Aligned Currents: Steady State Solutions, ”
    Russell, A. J. B., Wright, A. N. and Hood, A. W.
    J. Geophys. Res., accepted, 2009.

  4. “Coronal Alfven Speeds in an Isothermal Atmosphere: II. Alfven Speed Profiles and Fundamental Modes,”
    Regnier, S., Russell, A. J. B., Hood, A. W. and Priest, E. R.
    In preparation, 2010.
(List is correct as of 7th Jan 2010. Citation count obtained from the Astrophysics Data System.)

Brief Summaries
  1. Previous research has shown a strong correlation between subphotospheric flows and flaring for solar active regions. Furthermore, magnetograms show that active region flux consists of many “fragments” over a range of scales. Could fragmentation link flows and flaring? We performed the first analysis of distributions of active region flux for a statistically significant number of active regions. The distributions were lognormal, supporting the hypothesis that active regions originate from a single flux tube that is broken up repeated, random divisions. We also demonstrated that the degree of fragmentation correlates with neither flows not flaring, pointing towards the injection of magnetic twist into the corona as a likelier contribution to flare energy output.

  2. The resonant coupling of fast and kink like waves to Alfven waves is a hot topic. A better understanding will tell us how energy propagates in the solar system and what spatial scales are involved. The 2D problem, in which the equilibrium varies in 2D across the background magnetic field, is vital to our understanding of the damping of coronal loop oscillations, and the flow of energy from the solar wind to the ionosphere through Ultra Low Frequency waves. This paper presents the first full, analytic solution for such equilibria, and confirms key features through numerical simulations. Excitingly, we are able to explain the distribution of energy density in the resonant Alfven waves: this will lead to better and more ambitious probing of the magnetosphere via seismology; it also explains a mysterious feature of cutting edge simulations from recent years.

  3. Field aligned currents, associated with aurora, deposit and remove electrons from the ionosphere. This modifies the ionospheric reflectivity, so the magnetosphere and the ionosphere form a coupled system. Can we predict the resulting “holes” in the ionosphere? Furthermore, downward current channels are often packed with small scale features. Energy is being transferred from large scales to small scales, but how? We applied an existing model to answer these questions, showing that we can indeed predict what the “holes” will look like, and demonstrating that a dynamic ionosphere leads to the production of fine scales in the magnetosphere, without relying feedback or non-linear effects.

  4. Stephane Regnier is leading efforts to develop models of the solar corona, extending magnetic field extrapolations to full magnetohydrodynamic equilibria. Following a seminar, we realised that his models would allow us to make the first theoretical predictions of the fundamental frequencies of oscillation of coronal field lines. This is a fundamental property that informs us about the character of waves in active regions, their penetration from the photosphere to the corona, and especially what happens to the energy in global p-mode oscillations. It also has obvious impact on coronal heating theories. For a sample of several active regions, we found a wide distribution in field line frequencies from mHz to Hz. This suggests that many frequencies will find their way into the corona, including global p-mode oscillations.
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