Deep convection pattern

From Memory Alpha, the free Star Trek reference

Deep convection patterns are variables that have to be taken into consideration when revitalizing a dying star.

When Doctor Timicin tried to revitalize Praxillus something went wrong and the star went nova. He couldn't explain what had happened, as he thought he had anticipated all variables, including the deep convection patterns, the proton reactions, and the neutrino count. (TNG: "Half a Life")