Abstract
The temporal variation of the electron density distribution observed by radio soundings at Rio Grande, Brazil during the eclipse of November 1966 has been analyzed. Using five models of chemical reaction coefficients and the lower boundary values of neutral constituents, the variation of an ‘equivalent’ temperature has been calculated. The equivalent temperature is that resulting from a minimization (over a range of heights and times) of the mean-square residual differences between the observed ∂N/∂t and the values calculated from the continuity equation. The equivalent temperature variations thus calculated may involve implicitly the effects of diurnal variations in the lower boundary values of neutral constituents and vertical drift velocities as well as the actual temperature variations. Assuming that the difference of the variation of the equivalent temperature between the eclipse and control day is mainly due to the difference of the vertical drift velocity, the additional vertical drift velocity on the eclipse day has been calculated; it is largely upward and starts to rise about 30min. before the ground eclipse for all five models. A simple model calculation indicates that this additional upward velocity could be caused by the effect of the reduced conductivity in the lower dynamo region during the eclipse.
