The source of the solar oscillations: Convective or magnetic?

Abstract

Abstract. The origin of solar oscillations has not yet been clearly determined. The downflows due to convective rapid cooling at the surface have been invoked as a possible source. In this paper we investigate the properties of the source as inferred from the local analysis of the intensity-velocity phase differences. The same spatial and temporal characteristics of other observed events and their correlation with the Hα bright points suggests downward plasma jets related to explosive chromospheric evaporation to be another possible candidate.

An interpretation of the $\vec{I-V}$ phase background based on observed plasma jets

“…The explosive chromospheric evaporation model (Fisher et al 1985) explains the main observed characteristics of those events whose spatial scales are of the order of a few arcsec and last for a few minutes . The same scales are those obtained by the analysis of the background locations maintaining spatial resolution (Moretti et al 2001a). Recently, observations in Hα and NaI D lines have shown a simultaneous occurrence of the impulsive brightenings (Warmuth et al 2000;Moretti et al 2001b).…”

“…Left, from top to bottom a-d) a simulation at 1 minute cadence of the intensity and velocity impulses a), the power spectra of the signals b) and the intensity-velocity phase spectrum c) for a 9h zero-padded time-series. d) the observed phase spectra at l = 100 for the NaI D lines obtained with 256 min runs at Naples (crosses) and Kanzelhöhe (diamonds), Moretti et al (2001a). The main properties of the measured I − V phase spectrum is reproduced by the simulation based on the observed characteristics of the impulsive events detected with similar systems and at the same spatial resolution.…”

“…A totally different explanation of the I − V phase difference background was recently forwarded by Moretti et al (2001a), proposing that downward directed plasma jets due to explosive events in the upper solar atmosphere contribute to the observed I − V signatures in the photosphere.…”

“…The presence of a solar background in the phase difference between the intensity and velocity (I − V) p-mode oscillation signals recently has been interpreted in terms of downflows due to convection (Skartlien & Rast 2000) or due to chromospheric explosive events (Moretti et al 2001a). In support of the latter, we present I and V characteristics of impulsive brightenings observed in the NaI D lines, show that these reproduce the frequency dependence of the I − V modulation background, and show that explanations invoking more frequently occurring phenomena such as seismic events are not likely in low-l modulation data.…”

Full-disk magnetic oscillations in the solar photosphere

“…5 and Fig. 1 in Moretti et al 2001). Results can depend on the techniques used by the different researches for the determination of the phase values, as described in Norton et al (2001).…”