Altitude of Two-Stream Irregularities in Equatorial E Region Using Sounding Rocket Experiments From Thumba

摘要

Amplitudes of two-stream irregularities and equatorial electrojet (EEJ) current are known to peak around the same altitude. Sounding rocket-borne magnetometer experiments have consistently shown that the EEJ current density maximizes around 105-km altitude whereas the theoretical models predict the EEJ peak around 100 km. One of the propositions to bridge this difference in the altitude has been based on the inclusion of small-scale turbulence (wavelength of <100 m) with the large-scale dynamics (kilometer size). This proposition is examined based on in situ measurements of E region electron density and plasma irregularities (two-stream and gradient-drift irregularities) obtained at different times of the day and night. These measurements were obtained based on sounding rocket flight experiments conducted from Thumba Equatorial Rocket Launching Station (8.54? N, 76.86? E), a facility in the vicinity of the dip equator. Whenever two-stream irregularities are present, the minimum electrojet current density is estimated based on the threshold velocity required for generation of these plasma irregularities. This method provides estimates of nighttime E region current also, which is difficult to measure. It is found that amplitudes of both two-stream irregularities and the estimated EEJ current peak around 105-km altitude irrespective of the presence or absence of the gradient-drift irregularities at the base of electrojet (95- to 100-km altitude).