Authors: Scott W. McIntosh, Bernhard Fleck
Affiliation: NASA Goddard Space Flight Center, USRA; European Space Agency,
Research and Scientific Support Department
Several recent investigations have shown that the plasma topography and chromospheric oscillations interact readily. Regions where the ratio of plasma and magnetic pressures are of order unity and the partitioning of the plasma's magnetic topology into open and closed regions have been demonstrated to be important in understanding the observations. To address the latter, using a new TRACE UV continua sequence, we study the properties of chromospheric oscillations in a place where open and closed magnetic topologies can be readily observed in the same field of view; an (equatorial) coronal hole. We ask the following: At the formation levels of the TRACE UV continua (in the upper photosphere or low chromosphere) can we see that the topographic structure of the coronal hole influences the passage of chromospheric oscillations and can the influence be measured? As a result of our study we show that there is a significant contrast in the signal phase-difference and travel-time between the portions of the TRACE field-of-view that are inside and outside of the coronal hole. For example, the derived travel-time of oscillations between the UV continua (in the frequency range of running sound waves; 6-8 mHz) inside the coronal hole is approximately eight seconds while that outside is of the order of four seconds. This result poses some interesting questions about the coronal hole, it's magnetic topology and significant changes in the plasma's thermodynamic stratification inside compared to that outside.