The method of updating the IRI-1990 model for the effects of large scale travelling ionospheric disturbances (LSTIDs) of the F-region have been established as a result of the statistical analysis of VI sounding data of European- Asian sector for 380 substorms. The effect of a LSTID occurring during a substorm is modelled as an additive correction to the quiet IRI foF2 and hmF2 values which depends on the time since the onset of the substorm and on the maximum AE-index value reached in it. In case of a sequence of substorms the additive corrections ΔfoF2 and ΔhmF2 are taking into account. The method for night-time ionosphere is described in detail, the listing of the FORTRAN-77 computer program is available on the floppy disk. The method is workable as correction to any ionospheric model.