Sunspot Prominences--Some Comparisons Between Limb and Disk Appearances

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Abstract
Three characteristic types of prominences associated with sunspots are considered with a view to correlating their limb and disk appearances. The discussion of the observations is carried out with special reference to: ( a ) type of associated spot-group, ( b ) form and dimensions of prominence filaments, ( c ) velocity and direction of motion in relation to adjacent sunspots, ( d ) magnetic polarity of sunspots at points of inflow. Type IIIa .—These are inflowing filaments moving along curved trajectories (not plane figures), which originate in the surrounding chromosphere or descend from “coronal clouds” formed above the spot area. They terminate on the boundary of the penumbra with a mean velocity of inflow of 48 km./sec. Their movements seem to be independent of the magnetic polarity of the attracting sunspots. The mean projected length is 61,000 km. Type IIIb .—Complex formations of loops and arches over spot-groups are rare. Single and double arches are frequently seen with the spectrohelioscope connecting adjacent spots of the same group. The direction of motion of the gases is upwards on one side and downwards on the other side of the arch: only one case has been observed where matter was clearly in descent on both sides of the same arch. The mean distance between the points of inflow and outflow is found to be 43,000 km., and the mean velocities at inflow and outflow +39. and −28 km./sec. respectively. The direction of motion is independent of the magnetic polarity of the spots concerned. Type IIIc .−These are flanking prominences, often of great dimensions, the form, growth and decay of which are intimately connected with the life-history of the adjacent spot-group. They exhibit great internal activity, as well as forming external streamers which leave the tops of the prominences to flow horizontally inwards and then downwards into the spot area. After a continued existence of days, or even weeks, they may suddenly become subject to disruptive forces, rising up bodily from the chromosphere with high velocity, to descend, at least partially, in large streamers into the spot-group. An example of this phenomenon is described as it appeared on the disk.

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