Equatorial evening prereversal vertical drift dependence on solar EUV flux and F10.7 index during quiet and disturbed periods over Brazil

A study of the dependence of the equatorial evening F region vertical drift velocity on solar EUV flux and F10.7 index is presented here, based on the vertical drift data obtained from Digisondes operated in São Luis (44.2° W, 2.33° S, dip angle: −2.7°) and Fortaleza (38.45° W, 3.9° S, dip angle: −11.5°) in Brazil. Previous studies on the vertical drift dependence on solar flux have addressed only the dependence on F10.7 index. The data analyzed here are from the months of October, November, and December of the years from 2001 to 2009, and the analysis was done for magnetically quiet and disturbed conditions. The results show that while the drift velocity peak is strongly dependent on both solar emission fluxes, the degrees of such dependence are higher for the EUV flux than for the F10.7 index in a consistent way as judged from its identical behavior at both São Luis and Fortaleza. The study also reveals different degrees of the vertical drift dependence on solar flux for magnetically quiet and disturbed conditions, the nature of which is investigated using an example of a storm time case study.

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