Spectra of complex Jovian S-storms can be interpreted as groups of tilted-V variants. In such an approach the basic components (wide-range S-bursts, narrow-range S-trains, emissions of type N, and shadow events) are arranged in a predictable sequence. It seems that the application of tilted-V variants offers some order for the chaos evident in many S-storm spectra.
Jupiter's S-storms can produce outstanding spectral records in the decametric range. The individual S-bursts are narrow-band emissions which may drift rapidly in the frequency domain and appear as tilted lines in the (dynamic) spectrum, i.e., in the orthogonal time-frequency plane. Drift rates may vary from -5 to -45 MHz s-l, while the instantaneous bandwidths are usually less than 200 kHz (Carr et al., 1983).
Many S-bursts are affiliated with other spectral features (Krausche et aE., . Probably the simplest of these is a combination of two S-bursts starting from a common origin but having different drift rates . If an L-burst is simultaneously present, the two Sbursts cut a tilted V-shaped opening in it, void of emission. This is known as a 'tilted-v' event (Riihimaa and Carr, 1981). It is shown here that the tilted-v event has variants, which are very common in the 20-25 MHz range and seem to be involved in many high-resolution S-spectra that exhibit complex structures.
A systematic study of tilted-V events was made from the records covering the periods August-December 1987 and September-November 1988 obtained with an acousto-optical radio spectrograph and a steerable twin crossed log-periodic antenna. Two parallel real-time records were made from the rightcircular component of the emission: one of the image on the transform plane, and the other of an intensity-modulated display driven by a charge-coupled device (RL 256EC/17). The latter was operated in the manner of a TV monitor but with line and frame frequencies of 2000 and 16 Hz, respectively. Since the recording is made with a continuous-motion shutterless camera, every other frame is blanked out to avoid overlapping, resulting in 40% effective sampling time.
A total of 12 S-storms were observed, 9 in the IO-B region and 3 in the IO-C region. The outstandingly interference-free location of the Kiiminki site (30 km east of Oulu) and the almost total absence of long-range radio station interference at night (especially in 1987) made it possible to use a wide-open RF amplifier. This has no frequency conversion and is therefore absolutely free of image-frequency