, Volume 89, Issue 1, pp 77-88

Evidence for temporal variations in polar plumes

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In order to place empirical constraints on possible plasma heating processes and acceleration mechanisms for mass flows in polar plumes, we studied the variability of the O vi and Mgx emissions from four plumes observed by the Harvard Skylab experiment. The observations consist of a 40 min sequence of spectroheliograms acquired with ∼2 min temporal resolution. We found that the Mgx emission from each plume had a strong ‘dc’ component and that any variations, if present, occurred at approximately the 10% (of the mean) level or less. This implies that temporal variations in the density and/or temperature were 5% or less. There were some statistically significant variations in the measured Mgx signals. Two of the plumes decreased in brightness by approximately 10% during the 40 min period of the observations. In addition two plumes exhibited short-term (few minute) variations which appear to be statistically significant at a confidence level of >90%. The latter variations (if real) appear to be due to small (∼2 × 104 K) fluctuations in temperature caused by fluctuations in the local plasma heating rate.