In the subauroral ionosphere, there are often observed narrow streams of fast subauroral ion drift to the west near the projection of the plasmopause at the height of the F-layer of the ionosphere. They are most noticeable during storms/substorms on the background of the large-scale plasma convection (Anderson et al., 1991;. For the first time, such streams were recorded with the Soviet satellite Kosmos-184, and they were called "polarization jet" (PJ; Gal'perin et al., 1973Gal'perin et al., , 1974. In the scientific literature, this phenomenon was also called "SubAuroral Ion Drifts" (SAIDs) after the paper of Spiro et al. (1979) where narrow streams of ion drifts were studied using data from the American satellite Atmosphere Explorer C (AE-C). The bandwidth of PJ/SAID at ionospheric heights is 1°-2° in latitude, and the drift velocity is ∼1 km/s and more in the westerly direction and is recorded in the evening and night MLT sectors. At the same time, broad flows are encountered in the evening sector (<20 MLT;Figueiredo et al., 2004;Karlsson et al., 1998;Yeh et al., 1991). Foster and Burke (2002) combined these two types of observations of subauroral electric fields: narrow jets of ion drift (PJ) and wide regions of ionospheric convection to the west with high velocities, called SubAuroral Polarization Stream (SAPS). These phenomena (SAPS and PJ) were studied with the satellite data, measurements by a chain of ground-based ionospheric stations, SuperDARN HF radars, and with the coherent scattering of radio signals (e.g.,

The existence of PJ/SAID (Polarization Jet (Galperin et al., 1974) or Subauroral Ion Drift (Spiro et al., 1979)) leads to a number of abrupt structural changes in the subauroral ionosphere, such as the appearance of plasma irregularities, the formation of a deep electron density trough at the height of the F-layer (Makarevich & Dyson, 2007;Volkov & Maltsev, 1992), thermospheric wind (Shubin & Deminov, 2019), vertical plasma transport (Anderson et al., 1991;Khalipov et al., 2016), which, having a significant impact on the conditions of radio wave propagation, reflect changes in space weather. Despite the fact that experimental and theoretical studies of PJ/SAID have been going on for several decades, its properties and nature have not been fully investigated, and the study of this phenomenon still remains one of the actual and important problems in the physics of the near-Earth environment.For the first time, a narrow stream of westward ion drift in the subauroral region of the ionosphere was detected according to the data of the Kosmos-184 satellite and was called the "polarization jet" (PJ) (Galperin et al., 1974). The name SAID is given to this phenomenon after the article (Spiro et al., 1979), in which it is discovered using data from Atmosphere Explorer C. Then, the large-scale properties of PJ/SAID and the mechanisms of its formation are studied using satellite and ground-based radar data (e.g.,

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