Equatorial spread F instability conditions as determined from ionograms

Conditions of plasma irregularity (or Spread F) generation under the Rayleigh-Taylor mechanism in the nighttime equatorial ionosphere are examined from ionogram data registered over Fortaleza (4°S, 38°W, mag. dip lat. −1.7°) Brazil for a one year period. The results show that local ionospheric conditions such as the bottomside F-region electron density scale length and the ion-neutral collision frequency at the base of the layer, at sunset hours, determine the generation of the spread F irregularities over the equator in the post sunset hours.

[1]  J. Bittencourt,et al.  IONIZATION DRIFT VELOCITIES IN THE EQUATORIAL F REGION , 1981 .

[2]  C. J. Zamlutti,et al.  Association between plasma bubble irregularities and airglow disturbances over Brazilian low latitudes , 1980 .

[3]  I. Batista,et al.  Some characteristics of spread F at the magnetic equatorial station Fortaleza , 1980 .

[4]  J. Owen,et al.  ALTAIR: an incoherent scatter radar for equatorial spread-F studies. Topical report 1 June 1977-1 January 1978 , 1979 .

[5]  G. Haerendel,et al.  The motion of depleted plasma regions in the equatorial ionosphere , 1979 .

[6]  M. Kelley,et al.  Late Time Barium Cloud Striations and Their Possible Relationship to Equatorial Spread F , 1979 .

[7]  E. Ott.  Theory of Rayleigh-Taylor bubbles in the equatorial ionosphere , 1978 .

[8]  R. Woodman,et al.  VHF radio wave scattering due to range and frequency types of equatorial spread-F , 1978 .

[9]  S. L. Ossakow,et al.  Morphological studies of rising equatorial Spread F bubbles. Interim report , 1977 .

[10]  B. C. Edgar,et al.  Equion, an Equatorial Ionospheric Irregularity Experiment , 1977 .

[11]  Ronald F. Woodman,et al.  Radar observations of F region equatorial irregularities , 1976 .

[12]  Anthony J. Scannapieco,et al.  Nonlinear equatorial spread F , 1976 .

[13]  Warner L. Ecklund,et al.  Evidence for a Rayleigh-Taylor type instability and upwelling of depleted density regions during equatorial spread F , 1976 .

[14]  M. Hudson,et al.  Linear theory of equatorial spread F , 1975 .

[15]  P. Kaw,et al.  Steady state finite amplitude Rayleigh Taylor modes in spread F , 1975 .

[16]  R. Greenwald,et al.  Equatorial spread F: Recent observations and a new interpretation , 1972 .

[17]  Ronald F. Woodman,et al.  Equatorial spread F: Implications of VHF radar observations , 1970 .

[18]  J. W. Dungey,et al.  Convective diffusion in the equatorial F region , 1956 .

[19]  Sidney L. Ossakow,et al.  Nonlinear equatorial spread F: The effect of neutral winds and background Pedersen conductivity , 1982 .

[20]  R. Tsunoda.  On the spatial relationship of 1-m equatorial spread F irregularities and plasma bubbles , 1980 .

[21]  S. Zalesak,et al.  Nonlinear equatorial spread F: dependence on altitude of the F peak and bottomside background electron density gradient scale length. Interim report , 1978 .