Universal time dependence of nighttime F region densities at high latitudes

Journal Article · Wed May 01 04:00:00 EDT 1985 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA090iA05p04319· OSTI ID:5646986

Beaujardiere, O D.L.; Wickwar, V B; Caudal, G; Holt, J M; Craven, J D; Frank, L A; Brace, L H; Evans, D S; Winningham, J D; Heelis, R A

Coordinated EISCAT, Chatanika, and Millstone Hill incoherent scatter radar observations have revealed that in the auroral zone, the nighttime F region densities vary substantially with the longitude of the observing site: EISCAT's densities are the largest and Millstone Hill's are the lowest. The nighttime F region densities measured by the individual radars are not uniform: the regions where the densities are maximum are the so-called ''blobs'' or ''patches'' that have been reported previously. The observations are consistent with the hypothesis that the nighttime densities are produced in significant amounts not by particle precipitation, but by solar EUV radiation, and that they have been transported across the polar cap. The observed differences can be explained by the offset of the geographic and geomagnetic poles. A larger portion of the magnetospheric convection pattern is sunlit when EISCAT is in the midnight sector than when Chatanika is. In winter, when Millstone Hill is in the midnight sector, almost all the auroral oval is in darkness. This universal time effect, which was observed on all coordinated three-radar experiments (September 1981 to February 1982), is illustrated using two periods of coincident radar and satellite observations: November 18--19, and December 15--16, 1981. These two periods were selected because they corresponded to relatively steady conditions. Dynamics Explorer (DE) measurements are used to aid in interpreting the radar observations. De 1 auroral images show what portion of the oval was sunlit. DE 2 data are used to measure the ion drift across the polar cap. Because the altitude of the ionization peak was high, the decay time of the F region density was substantially longer than the transit time across the polar cap.

• Research Organization: SRI International, Menlo Park, California
• OSTI ID: 5646986
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 90:A5; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640201* -- Atmospheric Physics-- Auroral
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AURORAL ZONES
DAILY VARIATIONS
DATA
EARTH ATMOSPHERE
ELECTROMAGNETIC RADIATION
ELECTRON DENSITY
EXPERIMENTAL DATA
EXTREME ULTRAVIOLET RADIATION
F REGION
GEOGRAPHICAL VARIATIONS
GEOMAGNETIC FIELD
INFORMATION
IONOSPHERE
MAGNETIC FIELDS
MAGNETOSPHERE
MEASURING INSTRUMENTS
NUMERICAL DATA
PLANETARY IONOSPHERES
POLAR REGIONS
RADAR
RADIATIONS
RANGE FINDERS
SATELLITES
ULTRAVIOLET RADIATION
VARIATIONS