Formation of polarization jet during injection of ions into the inner magnetosphere Original Research Article

Long-lasting ground based measurements of a polarization jet (PJ) by the latitudinal chain of ionospheric stations in Yakutia (3 < L < 5; MLT = UT + 9 h) and by 5 subauroral Russian stations were analyzed. A number of cases were found when PJ was recorded simultaneously with energetic ion observations by AMPTE/CCE and INTERBALL 2. The data comparison shows that at least in the considered cases of strong magnetic substorms, PJ was accompanied by strong injection of ions with the energy of ∼ 20 – 50 keV and intensity of ∼ 106 cm −2 c−1 ster−1 keV−1. Close to the injection region in the near midnight sector no ion dispersion was observed, but in the evening sector nose events were detected. In accordance with a mechanism suggested by Southwood and Wolf (1978) PJ was observed near the equatorial boundary of energetic ion penetration into the magnetosphere. Measurements by ionosondes at different longitudes show that the westward velocity of the front of PJ development is close to the gradient drift velocity of 20 keV ions (forming nose events). Thus, the physical mechanism of PJ formation due to energetic ion injection during a strong substorm burst is experimentally confirmed. Satellite measurements show that in the near midnight sector energetic ions reach the shell L = 3.0 in 20 – 30 minutes after a substorm commencement with AE > 500 nT.