A study of chromospheric oscillations using the SOHO and trace spacecraft

We analyze line and continuum time-series data of the solar atmosphere, wit h between 10 and 60 s cadence, using the MDI and SUMER instruments on the S OHO spacecraft and the UV bandpasses on the TRACE satellite. The co-aligned data sets sample spectral features formed from photosphere to the middle t ransition region, spanning five decades in pressure, under quiet-Sun and pl age conditions. We discuss power, phase difference, and coherence spectra, and examine data in the time domain. The observed photospheric and chromosp heric oscillations are strongly coupled for frequencies between 2 and 8 mHz . Phase coherences decrease with increasing height, with only occasional pe riods and locations of observable coherence up to heights where transition region emission lines are formed. The middle chromosphere tin the SUMER con tinual oscillates in several megameter (Mm) diameter coherent patches with power predominantly in the 5-7 mHz range. The TRACE data, formed in the upp er photosphere, show smaller patterns superimposed on these large-scale osc illations, resulting (at least in part) from granulation. At the observed s patial scales, all the observed properties point to p-modes, especially the "pseudomodes" just above the acoustic cutoff frequency, as the dominant mo de of the chromospheric dynamics. Smaller scale "acoustic event" drivers, a ssociated with granular dynamics, appear to be less important. The predomin ant internetwork chromospheric oscillations arise from regions much larger horizontally than vertically. If propagating largely vertically, this can n aturally explain why the one-dimensional simulations of Carlsson & Stein mi ght be more successful than expected. The chromospheric response to the p-m ode driving is, however, intermittent in space and time. Some of the interm ittency appears to result from the interaction of the upward-propagating wa ves with magnetic fields. Evidence for this includes suppressed intensities and oscillations near quiet-Sun network elements (which we dub "magnetic s hadows"), absence of oscillations in internetwork regions neighboring plage magnetic fields, and a change in character of the quiet-Sun internetwork o scillations between the 119 and 104 nn continua formed at 1 and 1.2 Mm. The latter might be caused by canopy fields that form between these heights un der typical quiet-Sun conditions. A SUMER-only data set reported by Wikstal et al. has a factor of 3 more oscillatory power in the 104 nm continuum th an the data analyzed here, with stronger coherences extending into the sola r transition region. Together, these data support the general picture that the chromosphere oscillates primarily in response to forcing by the p-modes , they are therefore large-scale (several Mm across) waves, and they are of ten strongly influenced by magnetic effects (internetwork fields, or the ov erlying canopy), before the oscillations even reach the transition region.