ARTCC Controller reported an aircraft encountered a downdraft resulting in the aircraft losing altitude and flying below the MVA. The Controller vectored the aircraft towards an area of lower MVAs to avoid flight towards terrain.

Narrative

Aircraft X was IFR and on course flying from ZZZ to ZZZ1 level at 9;000ft. I had been soliciting and did not receive PIREPS reporting adverse ride conditions from other aircraft that day. I suddenly notice his altitude drop down to 8;600 ft. The aircraft was on VXXX and the MVA was 8;900ft. I immediately issued a low altitude alert to the aircraft to which the aircraft responded that they were trying to climb but were struggling with the downdraft. I asked the aircraft if they had the terrain in site and to maintain their own terrain and obstruction avoidance while they attempt to climb back up to 9;000ft. The next MVA block a few miles ahead was 8;000ft and another block up ahead was 10;800 ft (aircraft established on VXXX can be at 9;000ft in this block). I had lower terrain/MVAs about 10 miles east of the airway so once; the aircraft was in the 8;000ft block I vectored it out toward lower terrain just incase they experienced another downdraft (which they did).I don't think I would have done anything differently. I was unaware of the strong downdraft until that aircraft traveled through it and I am glad that I vectored the aircraft toward lower terrain when I did to ensure that the aircraft did not hit a mountain.