Arcs have time scales of minutes. Io-A and Io-C events generally have negative frequency drifts with vertex at the end of the arc. Io-B and Io-D generally show positive frequency drift with vertex at the beginning of the arc.
Riihimaa Modulations, noted by Dr. Jorma Riihimaa:
http://radiojove.gsfc.nasa.gov/library/newsletters/2012Jun/#1
have time scales of seconds and frequency drift generally in the +- 200 kHz/second:
http://herrero-radio-astronomy.blogspot.com/2013/12/arkhypov-and-rucker-2013-decametric.html
Figures 1 and 4
Solar Wind Modulations are very common in L Jovian radiation, with time scales of seconds and bands with little frequency drift (unlike S Jovian radiation with time scales of milliseconds or less). These modulations are caused by scattering from fluctuations in the Solar Wind:
Slee and Higgins 1968, "The solar wind and Jovian decametric radio emission"
http://adsabs.harvard.edu/abs/1968AuJPh..21..341S
