Discovery of EIT Wave

An "EIT wave" appears as the global propagation of brightness in  the solar corona followed by intensity dimness (Dimming) as seen in Extreme UltraViolet (EUV). It usually originates in the eruption or brusque filament disappearance. They were firstly discovered by the EUV Imager Telescope onboard SOHO (Principal Investigator is J.-P. Delaboudiniere). 

Thompson, B., et al, GRL, 25, 2465 (1998);

Moses,  D., et al., 1997, Sol. Phys.,175, 571 (1997);         

EIT wave enhanced image

The above picture was processed by the "EIT wave enhancement" procedure. See for comparison  the original image below. All other images shown here were also treated by this procedure.  

Original image

An unsolved fundamental question: is the EIT wave a real wave? The main puzzle is that its velocity can be as low as 50 km/s and cannot be a fast magneto-sonic wave as the Moreton wave. A Moreton wave is a similar event seen in the chromosphere (Ha), but much faster (characteristic velocities up to 2000 km/s).

	NEMO