Daytime vertical E x B drift velocities inferred from ground-based magnetometer observations at low latitudes

The daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100-120 km altitude region within +/- 2 degrees latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal ( H) component between a magnetometer placed directly on the magnetic equator and one displaced 6 degrees-9 degrees away. The difference between these measured H values provides a direct measure of the daytime electrojet current and, in turn, the magnitude of the vertical E x B drift velocity in the F region ionosphere. This paper discusses a recent study where 27 months of magnetometer H component observations and daytime, vertical E x B drift velocities were obtained in the Peruvian longitude sector between August 2001 and December 2003. In order to establish the relationships between Delta H and E x B drift velocities for the 270 days of observations, three approaches were chosen: (1) a linear regression analysis, (2) a multiple regression approach, and (3) a neural network approach. The neural network method gives slightly lower RMS error values compared with the other two methods. The relationships for all three techniques are validated using an independent set of E x B drift observations from the Jicamarca incoherent scatter radar (ISR) located at Jicamarca, Peru. The techniques presented here will be incorporated into a recently developed, real-time Global Assimilation of Ionospheric Measurements (GAIM) model.