Polar substorms include substorms observed at geomagnetic latitudes above 70° MLAT in the absence of simultaneous negative magnetic bays at lower latitudes, that is, substorms on the compressed contracted auroral oval. The general morphological features of polar substorms are considered based on the example of individual events registered on Svalbard arch. It is shown that polar substorms, like “classical” substorms, are characterized by the formation of a substorm current wedge and a steplike movement to the pole after the onset of a substorm, generation of Pi2 geomagnetic pulsations, and an increase of the PC-index of the polar cap before the onset of the substorm. At the same time, there are certain differences between polar substorms and “classical” substorms; namely, they start on more distant L-shells, develop in the region of a contracted auroral oval, occur at earlier pre-midnight hours, and generate only at low solar wind speeds and weakly disturbed geomagnetic conditions. It has been suggested that polar substorms may be a specific type of “classical” substorms that develop in the evening sector under magnetically quiet or weakly disturbed conditions when the auroral oval is concracted. The source of polar substorms may also be a local intensification of previously existing substorms in the post-midnight sector.

We have studied the geomagnetic conditions during the occurrence of auroral-hiss VLF emissions on the Earth’s surface in the form of noise bursts at frequencies above 5–6 kHz. The study is based on an analysis of auroral-hiss observations at auroral latitudes in northern Finland at Kannuslehto station (KAN, L ~ 5.5) during the winter campaigns of 2013–2018. It is shown that auroral-hiss bursts are most often observed in the interval of 20–01 MLT under low geomagnetic activity (Kp < 3). It has been found that the bursts are typical for the growth phase of a magnetospheric substorm; the bursts cease abruptly at the onset of the substorm (the break-up of auroras), which is apparently due to a drastic increase in the absorption of VLF waves in the ionosphere. The bursts are often accompanied by the generation of geomagnetic Pi2 pulsations. VLF observations have shown that auroral-hiss bursts are not observed on the Earth’s surface in the main phase of magnetic storms; however, they are typical of the recovery phase. It has been found from model data that, during the occurrence of auroral hiss, KAN station is usually projected to the near-equatorial region of the auroral oval or to the zone of diffuse precipitation of more energetic electrons, i.e., to lower latitudes than the typical position of visible auroras during that time.

The potential use of the wavelet-decomposition method developed by the authors for the analysis of geomagnetic data and cosmic ray variations is studied. With the use of adaptive threshold functions, the method allows the isolation of nonstationary, short-period (from 1 × 10–3 Hz and greater) variations in the data and the estimation of their parameters. Data from a network of ground-based magnetometers (www.inrtermagnet.org) and neutron monitors (http://cosray.unibe.ch/) were used in the work. The advantages of the method are shown on the example of magnetic storms on July 9 and September 27, 2017; the effectiveness of the method for the detection of low-amplitude anomalous variations in heterogeneous data has been proven experimentally. The dynamics of variations in the geomagnetic field at meridionally located stations and in the auroral zone is considered in detail; patterns of the occurrence and propagation of geomagnetic disturbances preceding and accompanying the intervals of magnetic storms are obtained. The application of the method made it possible to detect clearly and estimate weak short-term increases in geomagnetic activity observed against the background of increased cosmic ray intensity preceding the onset of magnetic storms. It is noted that the identified geomagnetic disturbances occurred synchronously at stations from high latitudes to the equator and correlated with the periods of southward turns of the IMF Bz component and increased auroral activity. During these intervals, cosmic rays exhibited low-amplitude Forbush effects, which were detected with this method.