Low-latitudeDScomponent of geomagnetic storm field

Relationships between the low-latitude DS component and the intensity of auroral electrojet are examined for several intense geomagnetic storms. It is shown that the magnitude of the DS component fluctuates considerably during the course of a storm and that magnetospheric substorms are responsible for the fluctuations. In particular, during the main phase many substorms are associated with a temporary decrease of DS during its early phase and with a subsequent increase during a later phase. Therefore there temporarily occurs a strong anticorrelation between DS and the electrojet intensity. The origin of the DS component is discussed in the light of recent particle observations by the synchronous satellite ATS 5.