Core dimming ?
Ejection of emitting plasma from corona
Simultaneous drop of multiple emission lines, with roughly the same percentage decrease
Heating raises lower ionization states (e.g. a fraction of Fe IX becomes Fe X), cooling does the opposite
Heating: Emission loss in lines with lower formation temperatures with roughly simultaneous emission gain in lines with higher formation temperatures. Cooling: reverse of above
Dim feature (e.g. filament) moves between observing location and bright feature (e.g. flare arcade)
Drop of emission lines proportional to their absorption cross section in the obscuring material. Also apparent in EUV images
Waves Global dimming?
Shocks propagate globally, causing compression/rarefaction of plasma
Apparent in EUV images, especially using difference movies
Doppler shift dimming
Fast moving plasma causes Doppler shift of emissions, which could start to shift outside instrument bandpass
Doppler shift is seen in spectral measurements (e.g. EVE)