Abstract
Abstract Rocket-borne in-situ measurements of electron density and current density made from Thumba, India, on four occasions between 1966 and 1973 and on one flight from Peru in 1965 are studied along with the corresponding ground magnetometer data. The Cowling conductivity is computed using the yearly mean magnetic field values of 1965 and the atmospheric density values from the MSIS 1986 model. The rocket-borne measurements from Thumba cover different geophysical conditions of strong, moderate and partial counter-electrojet events. The vertical profiles of the measured current density and electron density are presented along with the computed Cowling conductivity, electron drift velocity and electric field. The peak current density occurred at 106–107 km over Thumba and at 109 km over Peru compared to 104 km over Brazil. Cowling conductivity peaks occurred at 102 km over Huancayo and 101 km over Thumba, while electron drift velocity and electric field peaks occurred at approximately 105–107 km over Thumba, 108 and 110 km over Huancayo and 104 km over Brazil, respectively. While the electron density near the level of peak current density shows some variability, electron drift velocity and electric field show large variability. We conclude that the local electric field plays an important role in the spatial and temporal variability of the strength of the electrojet.
Highlights
Enhancement of the solar daily range of the horizontal component of the geomagnetic field H, as detected abovePeru, was explained by Chapman (1951) as being due to a band of intense electric current in the E-region of the ionosphere within ±3◦ dip latitude; subsequently denoted as the Equatorial Electrojet (EEJ)
We report a study of the equatorial electrojet (EEJ) using the in situ rocket-borne measurements of plasma density and current density from Thumba (India) and Peru along with the ground magnetometer data
The conversion of the probe current to electron density was calibrated using the critical frequency of the E region, fo E, from the ionosonde at Thumba or Kodaikanal
Summary
Enhancement of the solar daily range of the horizontal component of the geomagnetic field H , as detected abovePeru, was explained by Chapman (1951) as being due to a band of intense electric current in the E-region of the ionosphere within ±3◦ dip latitude; subsequently denoted as the Equatorial Electrojet (EEJ). The unique geometry of the orthogonal electric and magnetic fields and the different vertical mobility of electrons and ions in the E-region cause a vertical Hall polarization field, which in turn increases the electrical conductivity over the magnetic equator (Cowling and Borger, 1948). This causes a large current over the dip equator with the same dynamo electric field that found at other latitudes (Baker and Martyn, 1953).
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