Plasma line technique to measure sub-second electron density with Sondrestrom ISR

During auroral substorm events, various large and fine-scale auroral structures evolve rapidly in high-latitude ionosphere. The electron density associated with fine-scale structures often changes on a millisecond time-scale and attain high values. The evolution of density structures can point to the source mechanism responsible. However, traditionally, it is difficult to measure the absolute electron density using ISRs with < 1s integration. At the Sondrestrom radar in Greenland, a new hardware and software installation has made it possible to measure wide-bandwidth incoherent scatter plasma line, and consequently, the electron density with a 200ms time resolution. This is possible in part to the high SNR of the Sondrestrom radar at its L-band frequency. We will discuss the radar properties allowing this measurement and the measurement technique with some examples.