Time-dependent transport of field-aligned bursts of electrons in flickering aurora

We have developed a time-dependent auroral electron transport model to stud y emission rates caused by field-aligned bursts of electrons (FABs) seen in flickering aurora. We simulate flickering FABs by turning on and off a dow nward electron intensity distribution at a given frequency. We assume this electron beam originates and is modulated at an altitude of 4000 km. We app ly collisionless transport from 4000 to 600 km and solve a time-dependent B oltzmann equation below 600 km. Because FABs have significant flux over a l arge energy range, dispersion has the most important effect on the resultin g emission rates. We find that for a 5 Wt flickering FAB, the column emissi on rate varies 93% from peak to valley, whereas for 100 Hz flickering, the variation in column emission rate is only 12% from peak to valley. This var iation is dependent on the frequency and source altitude. We show that with a time-dependent transport calculation and a filtered fast photometer or i mager looking in the zenith, it is possible to obtain an upper limit on the altitude from which the optical flickering originates. We also study what electron detectors on a rocket or satellite might measure in the lower iono sphere when there exists field-aligned bursts of electrons. Velocity disper sion calculations will give source altitudes much lower than is correct if they are derived from low energy electrons (<2 keV) measured at altitudes b elow 150 km. Our results agree with the interpretation that field-aligned b ursts are a temporal rather than spatial feature, and from this knowledge i t should be possible to reconstruct the initial electron distribution funct ion at the source altitude.