I refer to:
Flagg, Greenman, Reyes, and Carr, 1991, "A Catalog of High Resolution Jovian Decametric Radio Noise Burst Spectra, Volume 1" :
http://adsabs.harvard.edu/abs/1991STIN...9127047F
Section 3.5.2 describes N events.
I quote:
"...An N-event is a narrow band of emission which consists of either quasi continuous activity (narrow-band L-burst) or a train of narrow bandwidth S-bursts. The emission band is typically a few hundred kilohertz wide and often exhibits complex interactions with wide bandwidth S-bursts and other drifting features. N-events often exhibit exceptional frequency stability in the sense that the overall emission envelope may persist in a narrow frequency band for several minutes. Riihima has reported N-events lasting as long as 50 minutes while remaining within a 2 MHz wide frequency band [Riihimaa 1985]. At times, emission within the frequency boundaries of the N-event is very stable (Figure 3.4 A,B) and the upper and lower frequency edges of the emission remain nearly parallel. Sometimes the r Quasi-continuous emission within the N-event undulates rapidly in frequency. Interactions between N-events and wide frequency range S-bursts produce complex burst shapes and structures. While the burst character within an N event can be stable and unchanging over periods of tens of minutes it is also observed to change in character, switching between continuous emission and a narrow bandwidth S-burst train on a time scale of tens of seconds. The four moderate resolution AORS plates (3.21-3.24) show this type of N-event behavior near 30 Mhz..."
See also:
Riijimaa 1985 (Aarne Karjalainen Observatory, Oulu, Finland):
"Bursts of type N in Jupiter's decametric radio spectra"
http://adsabs.harvard.edu/abs/1985EM%26P...32....9R
Oya with 3 co authors 2002:
"Analyses Of Jovian Decametric Radiation S-Bursts Interacting With N-Bursts"
http://adsabs.harvard.edu/abs/2002EM%26P...88..187O