In this paper , we present the observations of two successive fast-mode extreme ultraviolet ( EUV ) wave events observed on 2016 July 23 .
Both fast-mode waves were observed by the Atmospheric Imaging Assembly ( AIA ) instrument on board the Solar Dynamics Observatory ( SDO ) satellite , with a traveling speed of \approx 675 and 640 km s ^ { -1 } , respectively .
These two wave events were associated with two filament eruptions and two GOES M-class solar flares from the NOAA active region 12565 , which was located near the western limb .
The EUV waves mainly move toward the south direction .
We observed the interaction of the EUV waves with a helmet streamer further away in the south .
When either or one of the EUV waves penetrates into the helmet streamer , a slowly propagating wave with a traveling speed of \approx 150 km s ^ { -1 } is observed along the streamer .
We suggest that the slowly-moving waves are slow-mode waves , and interpret this phenomenon as the magnetohydrodynamic ( MHD ) wave mode conversion from the fast mode to the slow mode .
Besides , we observed several stationary fronts in the north and south of the source region .