Development of auroral electrojets and low-latitude geomagnetic disturbances during strong magnetic storms on November 7-11, 2004

The influence of auroral electojets and solar wind parameters on variations in low-latitude geomagnetic disturbances and D (st) during strong magnetic storms on November 7-8, 2004 with D (st) a parts per thousand -380 nT and on November 9-10, 2004 with D (st) a parts per thousand -300 nT is studied on the basis of global geomagnetic observations. It is found that the impulsive variations of the western electrojet intensity with a duration of Delta t a parts per thousand 1-2 h (probably, substorm disturbances) lead to positive low-latitude disturbances of Delta H at I broken vertical bar aEuro(2) a parts per thousand 10A degrees aEuro30A degrees and to disturbances of the same durations with an amplitude +Delta H similar to 30-100 nT at latitudes of the polar cap (I broken vertical bar aEuro(2) a parts per thousand 75A degrees aEuro80A degrees). More durable (with Delta t a parts per thousand yen 10 h) convection electrojets whose centers are shifted to latitudes of similar to 50A degrees aEuro55A degrees in the process of storm development are the main cause of the increase in negative values of Delta H at low latitudes and D (st) . It is shown that meridional dynamics of position of the center of electrojets and the equatorial boundary of the auroral oval is governed by variations (increase or decrease) in the intensity of negative values of the IMF B (z) component. It is assumed that in these storms the intensification of the magnetospheric partially ring current closes the circuit to the ionosphere with the help of field-aligned currents at the equatorial boundary of the auroral oval is the main cause of the magnetic field depression at low latitudes.