Abstract <p>The glow accompanying a self-sustained subnanosecond discharge in nitrogen in the pressure range from 4 to 15 atm was recorded using the streak method. Breakdown delay time and pulse breakdown voltage of the discharge gap were recorded oscillographically. The experiments were carried out in uniform and non-uniform average electric fields. In these cases, the macro geometry of the discharge gap did not provide an increase in the electric field to the value necessary for the implementation of the electron runaway mode according to the classical runaway criterion. It is shown that at the initial stage of development, the discharge has a volumetric shape, which later turns into a spark. The discharge contraction, as a rule, begins from the cathode and the anode almost simultaneously. The conducted modeling of the dynamics of ionization processes showed that at the stage of the volumetric column formation, a short-term increase in the electric field near the anode occurs. As a result, the ionization of gas in the anode region increases sharply, which initiates the development of a spark channel, including from the anode.</p>