Quantifying perpendicularity of a distribution of azimuths

One of my current projects is an effort to quantify the spatial scales of energetic electron precipitation (EEP; also called energetic particle precipitation, EPP) signatures in the lower ionosphere using the World Wide Lightning Location Network (WWLLN) as an ionosphere remote sensor network. Current and previous work on EEP detection using subionospheric VLF remote sensing has typically relied on networks of receivers that monitor narrowband transmitters, like the AARDDVARK network. These networks are effective because the narrowband transmitter sources have operated reliably for many years, and are thus very well-characterized. Since the transmitters operate with a continuous carrier frequency, changes in the received signal can be detected at a frequency approaching the Nyquist frequency of the receiver. Because the transmitters and receivers in VLF networks are usually in fixed positions, the networks consist essentially of a relatively small number of fixed propagation paths that are continuously monitored.