Rapid Evolution of VHF ionospheric scintillation features with LOFAR

Recent data campaigns with the Low Frequency ARray (LOFAR) have revealed a wealth of new information about the dynamics of the mid-latitude ionosphere. Recent examples include the first observation of two simultaneous travelling ionospheric disturbances passing across each other at different altitudes (Fallows, et al., 2020). LOFAR data to date contains a wealth of different ionospheric structures many of which are previously un-reported. In this study we examine the sudden onset and rapid evolution of broadband ionospheric scintillation features from two radio sources, Cygnus A and Cassiopeia A, observed with the Irish LOFAR station in January 2019. A sudden transition from quiet ionospheric conditions to a largely coherent broadband series of power amplifications and fadings was observed as plasma structures pass across the line-of-sight. The role of possible driving processes is discussed. We emphasise that such features are just two out of a dataset exceeding over one hundred different cases, from different periods in the solar cycle, at different times of day, and in different seasonal conditions. There is limited previous coverage in the literature, and many of these features have only been seen once in the dataset.