HF Doppler spectrum under spread F and nonspread F conditions at magnetic equator

Measurement of vertical plasma drift in the F region at the magnetic equator is a direct measure of the east-west electric fields and provides valuable information about the electrodynamic processes in the region. The understanding of the F region plasma irregularities has advanced by the combination of theoretical and computer simulation studies along with ground based and space borne experiments. Scintillation studies in the VHF, UHF and GHz bands Rastogi also indicate the simultaneous presence of irregularities of varying scale sizes. The study of the spread F phenomenon gives insight into the plasma processes generating field aligned irregularities of varying scale sizes in the equatorial ionosphere. From the microlevel fluctuations in HF Doppler data and their spectra, it is possible to study the short period fluctuations in the F region electric fields. The authors study the Doppler spectra of the irregularities during spread F and nonspread F time and study their temporal evolution. Fourier analysis of Doppler data enables calculation of the velocity of the dominant irregularity and the velocity spreading. The temporal evolution of these two parameters are also studied and presented