The bremsstrahlung from high and relativistic energy electron precipitation (HEEP) measured with balloon based instruments provides information on energy spectra and fluence of the precipitating energetic electrons allowing calculations of the atmospheric ionization. HEEP from the outer radiation belt at the subauroral region causes an increase in the ionization rates down to about 20 km altitudes. We study the variability in the ionization rate using the balloon observations of secondary bremsstrahlung initiated by HEEP. For the first time the changes of atmospheric ionization rates on an hourly and minute time scale at different altitudes was retrieved from balloon observations. These new highlights are important for atmospheric electricity that is sensitive to the local condition in the atmosphere including the local ionization rate.