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Communications/Navigation Outage Forecasting System observational support for the equatorial E × B drift velocities associated with the four-cell tidal structures

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Abstract

[1] Previous studies have established the existence of a four-cell longitude pattern in equatorial F region ionospheric parameters such as total electron content and electron densities and in daytime, equatorial E × B drift velocities. This paper, for the first time, quantifies the longitude gradients in E × B drift associated with the four-cell tidal structures and confirms that these sharp gradients exist on a day-to-day basis. For this purpose, we use the Ion Velocity Meter (IVM) sensor on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite to obtain the daytime, vertical E × B drift velocities at the magnetic equator as a function of longitude, local time, and season. The IVM sensor measures the E × B drift velocity in three dimensions; however, we only use the E × B drift observations perpendicular to B in the meridional plane. These observations can be used to obtain the vertical E × B drifts at the magnetic equator by mapping along the geomagnetic field line. The period initially selected for this work covers several days in October, March, and December 2009. We find, on a day-to-day basis, that (1) sharp E × B drift gradients of −1.3 m s−1 deg−1 exist in the western Pacific sector during equinox, (2) sharp E × B drift gradients of +3 m s−1 deg−1 are observed in the eastern Pacific sector during equinox, and (3) sharp E × B drift gradients of −1.7 m s−1 deg−1 exist in the eastern Pacific sector during December solstice.

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