On the height variation of the E-region cowling conductivity – effect of charged dust particles

Abstract

Abstract. Height profiles of the Cowling conductivity in the electrojet region, estimated using the atmospheric parameters given by the existing models like CIRA or MSIS and measured electron density profiles, consistently show the heights of the electrojet current intensity peak to be more than 3 km below those estimated from in-situ measurements using magnetometers on board sounding rockets. Kulkarni and Muralikrishna (2005) attempted to explain this to be due to the effect of neutral dust particles. They reported that neutral dust particles, when they exist in sufficient numbers, can modify the collision parameters, especially in the lower E-region, where dust particles of meteoric origin are known to exist in large numbers, and thereby can modify the Cowling conductivity profile in the electrojet region. This work is extended here to include the effect of charged dust particles. Dust particles can become charged negatively by the attachment of ambient free electrons, and can thus reduce the number density of free electrons especially below the electrojet peak. This can alter the vertical profile of the east-west Hall current driven by the vertical Hall polarization field, thereby causing a net reduction in the electrojet current. Such a decrease in the electrojet current may be observed on the ground magnetograms. This mechanism, as proposed here, can operate only during periods of strong meteor shower activity, when the dust particle density at the assumed deposit height of 103 km can reach extreme values (for example, 5×10 4 cm −3 of 1-µm diameter dust particles). Such a dense dust layer may even cause a reversal in the normally upward vertical Hall polarization field, within the dust layer, causing a reversal of the electrojet currents below the current peak.

Extended study of extreme geoelectric field event scenarios for geomagnetically induced current applications

“…It is important to note that this phenomena is always present but is expected to be strongly amplified during certain severe/extreme geomagnetic storm events. The phenomena can be explained by the unique orthogonality orientation of the electric field and magnetic field and the vertical plasma drift in the ionospheric E‐region over the dip equator, which results in a large enhancement of the conductivity (i.e., Cowling conductivity) in the EEJ belt [ Rastogi , ; Muralikrishna and Kulkarni , ]. This leads to a larger current over the dip equator with the same E‐region electric field as at other low‐latitude stations outside the EEJ belt [ Baker and Martyn , ].…”

Saturn’s near-equatorial ionospheric conductivities from in situ measurements

“…. In fact, measurements in Earth's equatorial ionosphere 32 have shown that dust grains introduced by meteor ablation deplete the electron densities and decrease or indeed reverse the Hall and Cowling conductivities, a striking similarity to the effect of equatorial ring rain into Saturn's ionosphere.…”

The response of the dayside equatorial electrojet to step‐like changes of IMF BZ

“…For the selected northward turning events, the median increase in IMF B Z during the first 5 min is 5 nT, which corresponds to the reduction of the dawn‐to‐dusk IEF by 2 mV/m for a solar wind velocity of 400 km/s. For a height‐integrated Cowling conductance of 150 mho [ Rastogi and Chandra , ; Muralikrishna and Kulkarni , ], the reduction of the equatorial H component by 40+ nT can be attributed to the reduction of the EEF by 0.2 mV/m. Here we assumed that one third of the H reduction can be attributed to the ground‐induced current.…”