Ozone observations from the GOMOS instrument together with a coupled ion and neutral chemistry model are used to study the effects of the January 2005 solar storms on the polar winter middle atmosphere. The model results indicate strong HOx and NOx enhancements in the mesosphere, and simultaneous ozone depletion maximizing between 70--80 km. During strong proton forcing GOMOS measurements show the destruction of the tertiary ozone maximum, observed at polar latitudes near 72 km before the events. This altitude is concurrent with the largest HOx enhancements in the model results. We observe for the first time the disappearance of the tertiary ozone maximum, and determine the underlying cause. With subsiding proton forcing GOMOS measurements show the reappearance of the tertiary ozone maximum, returning to normal values by January 24. Our results indicate that even moderate solar events (>10 MeV proton flux of >5000 pfu) can cause significant ozone depletion (>70%) in the middle atmosphere.