[1] The present paper analyses the variations of daytime mesopause temperature and the Equatorial electrojet strength over the dip equator during December 2005 -March 2006 period, indicating a possible strong dynamical coupling between the two region through the intensification of planetary wave activity. The wave signatures (quasi 16-day period) are seen in the mesopause temperature and the electrojet-induced surface magnetic field, measured from Trivandrum (8.5°N, 76.5°E, 0.5°N diplat.), a geomagnetic dip equatorial station in India. This investigation reveals (1) amplification of the quasi 16-day wave in the equatorial mesopause temperature and the EEJ induced magnetic field (2) regular occurrence of Counter Electrojet (CEJ), with a periodicity of $16 days (3)

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Using the equivalent electrical circuit method for the theoretical treatment of the local wind effects on the equatorial electrojet, the height structures of electric fields and currents that are generated by height‐varying east‐west winds in the electrojet region have been calculated for theoretical model wind sturctures and for a variety of experimentally observed wind structures. The results bring out clearly the nature and extent of the local wind effects on the height and latitude structures of the equatorial electrojet. The more important conclusions of the present study are: (a) The vertical wind shears associated with tidal winds and gravity waves can generate significantly large electric fields and east‐west currents in the equatorial electrojet (EEJ). (b) The wind‐generated electric fields and currents are characterized by large height gradients, latitudinal gradients, and reversals of direction. (c) At the magnetic equator, wind‐generated electric fields and currents are often small (10%–30%) in comparison with the eastward electric‐field‐generated polarization field and east‐west currents around noon hours. (d) At geomagnetic latitudes of 3° and beyond the wind‐generated currents and electric fields often exceed those caused by the eastward electric field. (e) Beyond 2° the neutral winds can drastically alter the intensity and latitudinal structure of the EEJ, depending upon the magnitude and height location of the wind shear. (f) The observed variabilities in the ‘width’ and latitude structure of the EEJ can arise from the effects of such east‐west winds that have been observed experimentally.

On a geomagnetically disturbed night (7 January 2005), an equatorial spread F (ESF) event was captured during premidnight hours by the Indian MST radar (operated in ionospheric mode) at Gadanki (13.5°N, 79.2°E, dip angle 12.5°N). The base height of the ionospheric F region over dip equator and a low‐latitude station showed similar variation during most of the ESF interval except mainly during 2145–2200 IST (Indian standard time, IST = universal time, UT + 5.5 hours). The zonal electric field variation over dip equator responded to a “prompt penetration” event at ∼2000 IST by gradually changing its polarity from westward to eastward after ∼2015 IST leading to the initiation of ESF at ∼2035 IST. The linear growth rate analysis supports the generation of irregularities only when the eastward electric field owing to the “prompt penetration” effect is taken into account. The zonal electric field became westward again after 2100 IST. However, it ephemerally turned eastward shortly after ∼2145 IST (1615 UT) that is believed to be associated with an “overshielding” condition. A plasma plume got resurrected after ∼30 min indicating the association of the development of this plume structure with the overshielding electric field. The OI 630.0 nm airglow intensity variations observed by a collocated airglow photometer, simultaneously operated in a bidirectional (zenith and east) mode, corroborated well with the ESF structure and dynamics during the disturbed period. These observations evince the active role of interplanetary electric field (IEF) in the development of ESF in the premidnight hours.