Fast variations of ground irradiance in auroral regions

Variations in ground irradiance at frequencies >0.1 Hz may severely degrade the performance of automatic imaging systems. For this reason, measurements and analysis of fast variations in ground irradiance in the auroral region caused by variable auroral emissions have been performed. The largest amplitudes and fastest variations are found to occur during the active phase of geomagnetic substorms and during pulsating auroral conditions, respectively. The power spectra of the variations show a rapid decrease toward higher frequencies. Pulsating auroral conditions contain more power at higher frequencies than the active phase. On the average, similar to 10% of the total power in the spectra is at frequencies >0.3 Hz.