Abstract

Recent observations and analysis have revealed the presence of ubiquitous rapid upflows with velocities of order 50-150 km/s in the lower solar atmosphere. We have found signatures of these events in data from a broad range of imaging and spectroscopic instruments in the chromosphere, in the form... Show moreRecent observations and analysis have revealed the presence of ubiquitous rapid upflows with velocities of order 50-150 km/s in the lower solar atmosphere. We have found signatures of these events in data from a broad range of imaging and spectroscopic instruments in the chromosphere, in the form of spicules, and in the transition region (TR) and corona, in the form of blueward asymmetries of TR/coronal spectral line profiles, and propagating disturbances in coronal imaging. Preliminary analysis suggests that these upflows are part of a previously undetected, but relentless transfer of mass between the dense lower atmosphere and tenuous corona in which a potentially significant amount of plasma may be heated to coronal temperatures at very low heights, in the upper chromosphere, TR and low corona. There are many unresolved issues regarding the properties, formation mechanism and impact of these rapid upflow events. How ubiquitous are they? Do they occur at the footpoint regions of loops across whole active regions, or only at the edges? How do the upflow speeds vary with temperature? We perform a large sample study of active regions observed with Hinode/EIS and study the asymmetry of the TR and coronal lines for a large number of viewing angles (from center to limb) and magnetic field configurations. We also use double fits of gaussians to determine the velocity of high velocity component, and its variation as a function of temperature. These measurements can provide direct constraints for coronal heating models. Show less