Intensity Oscillations in the Upper Transition Region above Active Region Plage

Abstract

Although there are now many observations showing the presence of oscillations in the corona, almost no observational studies have focused on the bright upper transition region (TR) emission (the so-called moss) above active region plage. Here we report on a wavelet analysis of observations (made with the Transition Region and Coronal Explorer) of strong (~5%-15%) intensity oscillations in the upper TR footpoints of hot coronal loops. They show a range of periods from 200 to 600 s, typically persisting for 4-7 cycles. These oscillations are not associated with sunspots, as they usually occur at the periphery of plage regions. A preliminary comparison to photospheric vertical velocities (using the Michelson Doppler Imager on board the Solar and Heliospheric Observatory) reveals that some upper TR oscillations show a correlation with p-modes in the photosphere. In addition, a majority of the upper TR oscillations are directly associated with upper chromospheric oscillations observed in Hα, i.e., periodic flows in spicular structures. The presence of such strong oscillations at low heights (of the order of 3000 km) provides an ideal opportunity to study the propagation of oscillations from photosphere and chromosphere into the TR and corona. It can also help us understand the magnetic connectivity in the chromosphere and TR and shed light on the source of chromospheric mass flows such as spicules.