  Different ultraviolet (UV) and infrared (IR) auroral features have been
observed at Jupiter and Saturn. Using models related to UV and IR auroral
emissions, we estimate the characteristic time scales for the emissions, and
evaluate whether the observed differences between UV and IR emissions can be
understood by the differences in the emission time scales. Based on the model
results, the UV aurora at Jupiter and Saturn is directly related to excitation
by auroral electrons that impact molecular H2, occurring over a time scale of
0.01 sec. The IR auroral emission involves several time scales: while the
auroral ionization process and IR transitions occur over < 0.01 sec, the time
scale for ion chemistry is much longer at 0.01-10000 sec. Associated
atmospheric phenomena such as temperature variations and circulation are
effective over time scales of > 10000 sec. That is, for events that have a time
scale of ~100 sec, the ion chemistry, present in the IR but absent in the UV
emission process, could play a key role in producing a different features at
the two wavelengths. Applying these results to the observed Jovian polar UV
intensification events and the Io footprint aurora indicates that whether the
IR intensity varies in correlation with the UV or not depends on the number
flux of electrons and their characteristic energy.
