Solar chromospheric spicules from the leakage of photospheric oscillations and flows

摘要

Spicules are dynamic jets propelled upwards ( at speeds of similar to20 km s(-1)) from the solar 'surface' (photosphere) into the magnetized low atmosphere of the Sun(1-3). They carry a mass flux of 100 times that of the solar wind into the low solar corona(4). With diameters close to observational limits (< 500 km), spicules have been largely unexplained(3) since their discovery in 1877(5): none of the existing models(3) can account simultaneously for their ubiquity, evolution, energetics and recently discovered periodicity(6). Here we report a synthesis of modelling and high-spatial-resolution observations in which numerical simulations driven by observed photospheric velocities directly reproduce the observed occurrence and properties of individual spicules. Photospheric velocities are dominated by convective granulation ( which has been considered before for spicule formation(7-11)) and by p-modes ( which are solar global resonant acoustic oscillations visible in the photosphere as quasi-sinusoidal velocity and intensity pulsations). We show that the previously ignored p-modes are crucial: on inclined magnetic flux tubes, the p-modes leak sufficient energy from the global resonant cavity into the chromosphere to power shocks that drive upward flows and form spicules.