Polar geomagnetic disturbances

Results of recent observations of geomagnetic disturbances in both northern and southern high latitudes are critically reviewed, and various theories on these phenomena are introduced.In Section 1, an additional geomagnetic daily variation, observed in the polar areas on magnetically quiet days, is discussed. The quiet-day daily variation in the polar regions consists of the S_q⁰-field which is an extension of the S_q-field established in middle and low latitudes and an additional field, S_q^p, which is confined to the polar cap areas. The equivalent ionospheric electric current pattern of the S_q^p-field consists of two current vortices, clockwise on the morning side and counterclockwise on the afternoon side in the northern polar cap, when viewed from above, and their conjugate pattern in the southern polar cap. The intensity of S_q^p-field in local summer is about three times as large as that in local winter. This seasonal change can be attributed to the seasonal change in electric conductivity of the polar ionosphere. The S_q^p-field is interpreted as being caused by transferring, through the lines of geomagnetic force, the effect of two circular convections of the low-energy magnetospheric plasma driven by the solar wind.In Section 2, the morphology of the polar part of the sudden commencement of magnetic storms (SSC) is described. The polar part of the SSC field consists of the universal increase in the magnetic field due to the compression of the geomagnetic cavity by the storm solar wind and an additional polar field, DS(SSC), which can be represented by a transient enhancement of the S_q^p-field. A preliminary reverse impulse of SSC takes place only on the afternoon side in polar areas. It seems likely that these characteristics of the polar SSC can te interpreted, in a unified representation, as those of an initial transient phase of an elliptically polarized hydromagnetic wave which transports the compressing stage of the geomagnetic cavity.In Section 3, the morphology of the auroral electrojets is discussed on the basis that they are sporadic and intermittent phenomena. Opinions on the interpretation of the auroral electrojet are divided. The Chamberlain-Kern theory ascribing the electrojet to an electric polarization of precipitating proton-electron beams caused by a magnetic field gradient, seems to be the most plausible. It is certain that the S_q^p-field must be enhanced by the highly con- ductive auroral zones.In Section 4, the inter-relationship among the auroral electrojet intensity (ΔH), auroral luminosity (J) and auroral sporadic ionization (n) of the ionosphere is discussed. The relations expressed as J ∝ n² and J ∝ (ΔH)² hold especially well in the auroral zones. Electron beams of 10 keV average energy accompanied by protons seem to be the most probable agency to result in these relations.In Section 5, results of observational studies on the conjugate relationship for geomagnetic bays and giant magnetic pulsations observed in high latitudes are summarized. A conjugate of stations are defined with respect to the unperturbed geomagnetic field. Similarity and simultaneity of geomagnetic bays at the conjugate areas are good. The activated areas for individual bays are several degrees in latitude and 10–30 degrees in longitude at their well developed stage. The conjugacy holds between the conjugately activated areas. Geomagnetic pulsations of several minutes in period and several hundred gammas in amplitude observed at high latitudes also have a very good conjugacy. They are interpreted as elliptically polarized transverse hydromagnetic waves generated in the magnetosphere and transmitted along the lines of geomagnetic force towards the Earth. The polarization vectors rotate counter-clockwise on the morning side and clockwise on the afternoon side, looking along the direction of the lines of force. The morning pulsations having larger amplitude and the afternoon ones having smaller amplitude, may be identified with the anisotropic and isotropic modes respectively of the polarized transverse hydromagnetic waves.In Section 6, the so-called spiral patterns of polar magnetic disturbances are discussed. A large number of spiral patterns of polar upper atmospheric disturbance have been proposed. It seems likely that only a spiral locus of ionospheric blackout on the morning side is the real Størmer orbit of proton impact and that the others may be identified with some part of a closed curve of an oval shape which is ascribed to the projection of the radiation belt of particles (either electrons or protons) trapped by a distorted geomagnetic field along the lines of the magnetic force upon the polar ionosphere.Section 7 deals with gaps in the existing knowledge of polar magnetic disturbances.