Abstract

We explore the limb-to-limb behavior of multi-frequency Transition Region and Coronal Explorer (TRACE) travel-time measurements of magneto-atmospheric waves in the solar chromosphere. We establish that while the higher frequency acoustic travel-times (~ 7~mHz) show little or no limb-to-limb varia... Show moreWe explore the limb-to-limb behavior of multi-frequency Transition Region and Coronal Explorer (TRACE) travel-time measurements of magneto-atmospheric waves in the solar chromosphere. We establish that while the higher frequency acoustic travel-times (~ 7~mHz) show little or no limb-to-limb variation, the previously documented variations of travel-time measurements on the magnetic environment through which the waves propagate are evident: increased travel-times in coronal holes; decreased travel-times in strong closed magnetic concentrations. For frequencies approaching the classical acoustic cut-off frequency (5.2~mHz) and below there is an increasing dependence of the measured travel-time with viewing angle and decreasing frequency. In this paper we demonstrate, using supporting observations from the Solar Optical Telescope on Hinode, that the center-to-limb variation of the low-frequency travel-times is the signature of propagating waves on magnetic network structures at granular spatial scales [i.e., structures close the spatial Nyquist frequency of TRACE] whose signal is a result of sub-resolution UV emission line 'contamination' in the 1600Å passband. Further, these structures must have a line-of-sight extension normal to the solar surface that increases across the disk as we approach the limb. We deduce that the low- frequency travel-time signal is directly caused by spicule motions which are increasingly inclined to the TRACE line-of-sight. Similarly, using SOT support, we propose that the apparent TRACE travel-time enhancement in coronal holes from TRACE, at same granular network locations, is the result of a change in vertical stratification in the coronal hole compared to quiet Sun counterpart emission. This effort is of particular relevance to full-disk travel-time investigations from the Solar Dynamics Observatory. Show less