Role of equatorial ionization anomaly in the initiation of equatorial spread F
A comparative study is made of the changes in the latitudinal structure of the F region electron density at fixed altitudes in the Indian equatorial region on days with and without postsunset onset of equatorial spread F, using (N-h) profile data of Ahmedabad (dip latitude 18.6/sup 0/N), Waltair (Dip latitude 10.6/sup 0/N), and Kodaikanal (dip latitude 1.5/sup 0/N). It is found that on spread F days the ratio of the electron density in the altitude region 370--300 km between Ahmedabad and Waltair showed a sudden enhancement starting at 1700 LT by a factor of 8 to 30 (at 1900 LT) from a near-constant value of about 2 during the daytime. No such enhancement of the density ratio was evidenced on days without spread F. The enhancement of the electron density ratio prior to the onset of spread F is interpreted as an intensification of the northern crest of the equatorial anomaly, with the ionization in the bottomside F region as far north as 9/sup 0/ from the dip equator participating in the crest intensification process. The rapid intensification of the ionization anomaly engenders a similar augmentation of the neutral anomaly around sunset hours. This in turn creates a localized cell of altitude dependent equatorward neutral wind that aids further intensification of the crests of both the anomalies and augmentation of ionization in the magnetic field line tube passing through the height of maximum plasma density of the F/sub 2/ layer over the equator. The net result of these coupling processes is a weakening of the ambient transequatorial wind (particularly during northern winter months) and reduction of the north-south asymmetry of the ionization anomaly crest, a condition favorable for the onset of spread F (Maruyama and Matuura, 1984).
- Research Organization:
- Physical Research Laboratory, Ahmedabad, India
- OSTI ID:
- 6839660
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 93:A6
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
SPREAD F
ELECTRON DENSITY
ALTITUDE
DAILY VARIATIONS
EQUATOR
INDIA
IONIZATION
LATITUDE EFFECT
MAGNETIC FIELDS
PLASMA DENSITY
WIND
ASIA
DEVELOPING COUNTRIES
EARTH ATMOSPHERE
F REGION
GEOGRAPHICAL VARIATIONS
IONOSPHERE
PLANETARY IONOSPHERES
VARIATIONS
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena