Perturbed electric fields in the earth’s ionosphere during storm activities may result from the penetration electric fields from high latitudes and/or from the dynamo mechanism driven by the neutral disturbances,depending on the storm phases.In general,the identification of the penetration electric fields is easier than that of the dynamo electric fields.At times,the latter becomes invisible or difficult to identify.This is an interesting problem which motivates a model study to investigate the possible reasons.Model runs made from the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR/TIEGCM) will be presented.Theoretical studies of ionospheric responses to geomagnetic storms with model simulations indicate that the intensities of disturbance dynamo electric fields are highly dependent on various parameters,for example,solar activities,seasonal effects anduniversal times,etc.When geomagnetic activities commence at 01～07 UT in summer solstices with low solar fluxes,the disturbance dynamo electric fields become very small.As comparedwith the general daily variations,it seems to be invisible.For other cases,the magnitudes of the dynamo electric fields are relatively larger under the same geomagnetic activities.