Estimating Daytime, Vertical Exb Drift Velocities In The Equatorial Fregion Using Ground-Based Magnetometer Observations

The daytime equatorial electrojet is a narrow band of<br>enhanced eastward current flowing in the 100 to 120<br>km altitude region within +/- 2 degrees latitude of the<br>dip equator. The strength of the electrojet varies<br>considerably from day-to-day and has its origin in the<br>Solar quiet (Sq) current dynamo mechanism and the<br>penetration of electric fields from high latitudes. A<br>unique way of determining the daytime strength of<br>the electrojet is to observe the difference in the magnitudes<br>of the Horizontal (H) component between a<br>magnetometer placed directly on the magnetic equator<br>and one displaced 6 to 9 degrees away. The difference<br>between these measured H values provides a<br>direct measure of the daytime electrojet current, and<br>in turn, the magnitude of the vertical ExB drift velocity<br>in the F region ionosphere. This paper discusses a<br>recent study that has established the relationship between<br>the vertical ExB drift velocity in the ionospheric<br>F region and the daytime strength of the equatorial<br>electrojet in the South American (west coast) longitude<br>sector. Magnetometer H component observations<br>from Canete (0.8 N. dip lat.) and Piura (6.8 N. dip<br>lat.) in Peru and daytime, vertical ExB drift velocities<br>measured by the Jicamarca Incoherent Scatter Radar<br>(ISR) Facility have been used to establish this relationship.<br>The magnetometer observations and the ISR<br>drift measurements were obtained for the period between<br>July, 1998 and June, 1999.