Kinematical characterization of intensity fluctuations observed in STEREO EUVI images: II. Off-disk case

Coherent quasi-periodic perturbations in brightness along polar plumes have been found with the Extreme ultraviolet Imager Telescope (EIT) onboard the SOlar and Heliospheric Observatory (SOHO). Unfortunately, without the use of high cadence EIT campaigns from SOHO, a systematic study of such phenomenon was not feasible due to the high temporal resolution required for this analysis. The advent of the Solar TErrestrial RElationships Observatory (STEREO) mission with its higher spatial and temporal resolution imagers resolved this issue. The twin Extreme UltraViolet Imagers (EUVI) aboard STEREO allowed for simultaneous, high cadence views of the plume structures from two view points. In our enhanced, wavelet processed STEREO/EUVI images, we have found persistent and quasi-steady intensity fluctuations apparently traveling outward above polar coronal holes. The projected plane-of-sky linear speed ranges from 70 to 150 km/sec for these above-the-limb fluctuations. Additionally, some cases exhibit an acceleration pattern very close to the limb. In this work, we introduce the method developed to systematically measure the kinematical parameters of the phenomenon, we compute several parameters for pre-selected dates, and we discuss the existence of an apparent quasi-periodic pattern observed in the Height-Time maps. Finally, we relate our quantitative findings to previous works.