NSWP: Equatorial Investigations in the Pacific Sector

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This project will address a priority goal of the National Space Weather Program, the need for able short-term forecasts of intense ionospheric irregularities in plasma density that develop in the nighttime equatorial F region (referred to as equatorial spread F, or ESF). Currently, ESF cannot be predicted on a day-to-day basis, even up to less than an hour before the expected first appearance of ESF. There is growing evidence that a key, though unheralded, player may be large-scale wave structure (LSWS) that develops in the bottomside F layer, whereas many previous efforts focused on the post-sunset rise of the F region at dusk. Recent research suggests that measurements of the velocity of the post-sunset rise may be contaminated by the large-scale wave structure, which may help explain why the control of ESF by the post-sunset rise, which holds climatologically, breaks down on a day-to-day basis. This project will investigate the relationships among the large scale wave structure, the post sunset rise, and ESF. The detection and characterization of the large scale wave structures require use of a radar with a steerable beam or sensors spaced closely in longitude. Currently, the only sensors of this kind are the multi-beam radars on the island of Pohnpei and Christmas Island as well as the steerable incoherent-scatter radar ALTAIR located in Kwajalein. The project will use the datasets to perform the following tasks: (1) Use three-beam radar data collected over seven years at Pohnpei, and two-beam radar data collected over four years at Christmas Island, to determine the presence of large scale wave structure and to extract the true post-sunset rise velocity; (2) Operate the recently reconfigured five-beam radar at Pohnpei in order to acquire data which will enable determination of the horizontal wavelength of the large scale wave structure; (3 ) Use all data collected by both radars, each spanning a full solar cycle, to determine short-term and long-term relationships among large scale wave structure, the post-sunset rise, and ESF. The proposed effort is expected to yield the first database with information on large scale waves structure, the post sunset rise, and ESF containing continuous measurements from two locations in the central Pacific sector that span a single, full solar cycle This database can be used for various investigations on time scales from a minute to a full single solar cycle and will be suitable for support of satellite programs such as CHAMP, ROCSAT, DMSP, TIMED, Formosat, and C/NOFS.