High-frequency Waves in Chromospheric Spicules

Abstract

Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules captured above the solar limb. At five equally separated atmospheric heights, spanning approximately 4900–7500 km, we have detected a total of 15,959 individual wave events, with a mean displacement amplitude of 151 ± 124 km, a mean period of 54 ± 45 s, and a mean projected velocity amplitude of 21 ± 13 km s−1. We find that both the displacement and velocity amplitudes increase with height above the solar limb, ranging from 132 ± 111 km and 17.7 ± 10.6 km s−1 at ≈4900 km, and 168 ± 125 km and 26.3 ± 14.1 km s−1 at ≈7500 km, respectively. Following the examination of neighboring oscillations in time and space, we find 45% of the waves to be upwardly propagating, 49% to be downwardly propagating, and 6% to be standing, with mean absolute phase velocities for the propagating waves on the order of 75–150 km s−1. While the energy flux of the waves propagating downwards does not appear to depend on height, we find the energy flux of the upwardly propagating waves decreases with atmospheric height at a rate of −13,200 ± 6500 W m−2/Mm. As a result, this decrease in energy flux as the waves propagate upwards may provide significant thermal input into the local plasma.