A Preliminary Report on Chromospheric Spicules of Extremely Short Lifetime.

Abstract

Small spikes of chromospheric material, observed in Ha with the coronagraph and quartz-polaroid monochromator, are described. These spicules, seen in polar regions of the sun, have very brief lifetimes, amounting on the average to 4 or 5 minutes. The typical spicule is low in brightness and has a height at maximum of less than 15 seconds of arc. At least in polar regions, they appear to be present in greater or smaller numbers at all times. The spicules are apparently distributed at random in the polar regions studied. The behavior of the spikes, while well typed, exhibits considerable variation. Possible association with polar coronal "plumes" and with "rice grains" of the disk is discussed.For many years solar observers have been aware of the irregular appearance of the chromosphere of the sun when viewed under the best observing conditions. Frequent reference has been made to Secchi's observations of the "vertical flames" of the chromosphere in polar regions of the sun. 1 In discussing Lick Observatory eclipse photographs Menzel has called attention 2 to the "spike" prominences of the chromosphere and to the fact that "the difference between the chromosphere and the prominences is merely one of I degree." The irregularities of the chromosphere are evident in the eclipse photographs reproduced by Menzel and, still more strikingly, in the photographs taken by Marriott, of ' Swarthmore College, at the eclipse of October, 1930. In the latter, small vertical polar prominences are clearly visible in some sections of the solar limb. During the fall of 1943 I noticed that small chromospheric spike prominences were clearly discernible in photographs of the polar regions of the sun which I was taking with the Lyot-type coronagraph of the Harvard College Observatory located at Climax, Colorado. I was amazed at the extremely brief lifetimes and the great frequency of occurrence which visual observations of these spicules indicated. Consequently, I decided, toward the end of the year, to undertake a further investigation of this interesting phenomenon. On December 12, 1943, under the very best conditions of atmospheric steadiness and purity, I obtained a motion-picture film centered near the position angle of the north pole of solar rotation. The 35-mm film was exposed at a rate of one picture per minute through an interference polarization monochromator designed and built by Dr. John W. Evans 3 and similar to that used by Pettit for prominence observations. 4 Exposures were about 2 seconds on a 103 Ha sensitization film produced especially by Eastman Kodak Company. With a red-glass filter and the special film, the over-all transmission band utilized was about 4 A wide, centered on 6563 A oí Ha.From this first film and from subsequent visual and photographic observations I have ascertained, at least roughly, the behavior of the typical polar chromospheric spicule. The typical spicule shows first as a barely detectable lump on the solar limb. The lump rapidly enlarges and brightens to a maximum intensity that is still relat...

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