HR: 1340h
AN: SA43A-1094    [Abstracts]
TI: Quasi-periodic Variations of 2 to 4 Days in the Electron Density of the Post Sunset Equatorial Anomaly Observed to be Synchronous on a Planetary Sale.
AU: * Whalen, J A
EM: james.whalen@hanscom.af.mil
AF: Space Vehicles Directorate Air Force Research Laboratory, 29 Randolph Road, Hanscom AFB, MA 01731-3010 United States
AB: Quasi-periodic variations are observed in the F layer maximum electron density of the post sunset equatorial anomaly at its temporal maximum which occurs near 2100 LT. Periods are 3-4 days in Oct-Jan and about 2 days in Mar-Apr; magnitudes are large, peak-to-valley ratios being between 2 and 5; conditions are solar maximum. Observations are by ionospheric sounders in the American sector at magnetically conjugate locations in Northern and Southern hemispheres, and at Okinawa in the northern anomaly of Eastern Asia. The variations are synchronous in that the dates of each maximum and of each minimum coincide at all locations, day-to-day continuously for month-long periods. This relation exists although measurements in the American sector are at 02 UT and those at Okinawa are at 12 UT. In addition, the magnetically conjugate variations are simultaneous, which is evidence that the variations are a product of pre-reversal ExB drift velocity. These variations are similar both in frequency and in their episodic nature to those observed principally in the daytime anomaly where they are attributed to planetary scale oscillations in the neutral mesospheric zonal winds. If the variations reported here have a similar cause, it raises the possibility that the magnitude of the electron density of the anomaly - and therefore the conditions under which scintillation on trans-ionospheric RF signals can occur - can be forecast by two means: by the quasi-periodic repetition of the variations; and by the observation of planetary waves in the mesosphere by the TIMED satellite.
DE: 2415 Equatorial ionosphere
DE: 2437 Ionospheric dynamics
DE: 2447 Modeling and forecasting
DE: 3332 Mesospheric dynamics
DE: 3389 Tides and planetary waves
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005