Abstract:
Using time series data of spectral lines originating from a wide range of temperatures in the solar
transition region, above a polar coronal hole, from SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
on SoHO (Solar and Heliospheric Observatory), we report on the detection of very long (≈170 min) periodic
intensity fluctuations, above the limb. Our data also reveal long periodicities (10-90 min), previously observed
with other SoHO instruments. With the acoustic cut-off frequency implying a maximum allowable period of ≈
90 min, it is unclear whether these intensity fluctuations are due to waves or are the result of a recurrent magnetic
reconnection process.
