Equatorial plasma irregularities in the ionospheric F-region proliferate after sunset, causing the most apparent radio scintillation “hot-spot” in geospace. These irregularities are caused by plasma instabilities, and appear mostly in the form of under-densities that rise up from the F-region’s bottomside. After an irregularity production peak at sunset, the amplitude of the resulting turbulence decays with time. Analyzing a large database of plasma irregularity spectra observed by one of the European Space Agency’s Swarm satellites, we have applied a novel but conceptually simple statistical analysis to the data, finding in the process that post-sunset turbulence in the F-region tends to decay with a uniform, scale-independent rate at night, thereby confirming and extending the results from earlier case studies. Our results should be of utility for large-scale space weather modelling efforts that are unable to resolve turbulent effects.