Core dimming

Mass loss

Ejection of emitting plasma from corona

Simultaneous drop of multiple emission lines, with roughly the same percentage decrease

Thermal dimming

Temperature evolution

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

Obscuration dimming

Obscuration

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

Global dimming?

Waves

Shocks propagate globally, causing compression/rarefaction of plasma

Apparent in EUV images, especially using difference movies

Doppler shift dimming

Doppler shift

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)