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On the generation of solar spicules and Alfvénic waves

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Science  23 Jun 2017:
Vol. 356, Issue 6344, pp. 1269-1272
DOI: 10.1126/science.aah5412

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Understanding the formation of spicules

Spicules are small jets lasting a few minutes that form in the solar atmosphere and propel hot plasma upward from the visible surface. The underlying physics of spicules is not well understood. Martínez-Sykora et al. developed radiation-magnetohydrodynamic simulations that can spontaneously produce numerous spicules with properties that match observations. Interactions between large-scale magnetic fields and the plasma, such as ambipolar diffusion, drive the formation process and subsequent evolution. Understanding how spicules form will help assess how much they heat the solar corona and how they relate to other solar phenomena.

Science, this issue p. 1269

Abstract

In the lower solar atmosphere, the chromosphere is permeated by jets known as spicules, in which plasma is propelled at speeds of 50 to 150 kilometers per second into the corona. The origin of the spicules is poorly understood, although they are expected to play a role in heating the million-degree corona and are associated with Alfvénic waves that help drive the solar wind. We compare magnetohydrodynamic simulations of spicules with observations from the Interface Region Imaging Spectrograph and the Swedish 1-m Solar Telescope. Spicules are shown to occur when magnetic tension is amplified and transported upward through interactions between ions and neutrals or ambipolar diffusion. The tension is impulsively released to drive flows, heat plasma (through ambipolar diffusion), and generate Alfvénic waves.

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