The prereversal enhancement in the vertical drift for Fortaleza and the sporadic E layer

Abstract

Using ionogram-recorded data for the location of Fortaleza ( 3 . 8 ∘ S, 38 . 0 ∘ W; magnetic latitude = - 6 ∘ ), the relation between the evening prereversal enhancement in the vertical F region plasma drift ( E × B ) and the diurnal variation of the sporadic E layer ( Es ) is examined. The database examined corresponds to the period of June 2001. The F region vertical drifts obtained as dh ′ F / dt for quiet days reveal that when the amplitudes of the evening prereversal enhancement (PRE) are higher, an interruption of an ongoing sporadic E layer is observed. A recent investigation by Abdu et al. [2003. Journal of Geophysical Research 108(A6), 1254. doi: 10.1029/2002JA009285.], showed that an upward electric field, intensified during the PRE, can be responsible for the inhibition of the sporadic E layer. In this work, we investigate the possible influence of a modified conductivity on the PRE development. The model developed by Batista et al. [1986. Journal of Geophysical Research 91(A11), 12055–12064.], based on the work of Heelis et al. [1974. Planetary and Space Science 22, 743–756.], was used to test the response of the PRE (its amplitude, time of occurrence and time of inversion) when the electrical conductivity of the E region is modified, specifically around sunset. The real cause of this modified conductivity is not investigated here, but the presence of a sporadic E layer could partially contribute to that. The causes of the agreement or disagreement between the computed and the observed value of vertical drift are discussed.