First simultaneous in situ measurement of electron density and electric field fluctuations during spread F in the Indian Zone

The paper presents results of in situ measurements of electron density and electric field fluctuations (δn e , δE' v and δE' H ) during a strong spread F event from the SHAR rocket range in India. Intermediate scale n e irregularities were observed in the F region valley over SHAR, which was earlier found to be free from irregularities. Experimental evidence of the validity of the image striation theory is provided through first simultaneous spectral measurement of electron density and electric field in the valley region. Correlation analysis of δn e , δE' v and δE' H suggests the existence of a sheared flow of current below the F‐peak. A new type of irregularity in the intermediate scale having a steep spectrum (n = −3.1) has also been detected in the valley region. A very sharp layer of ionization wherein the electron density increased by a factor of 50 in 10 km vertical extent was detected at 105 km.