Abstract
Abstract. During magnetic storms, the auroral electrojets intensification affects the thermospheric circulation on a global scale. This process which leads to electric field and current disturbance at middle and low latitudes, on the quiet day after the end of a storm, has been attributed to the ionospheric disturbance dynamo (Ddyn). The magnetic field disturbance observed as a result of this process is the reduction of the H component amplitude in the equatorial region which constitutes the main characteristic of the ionospheric disturbance dynamo process, associated with a westward electric current flow. The latitudinal profile of the Ddyn disturbance dynamo magnetic signature exhibits an eastward current at mid latitudes and a westward one at low latitudes with a substantial amplification at the magnetic equator. Such current flow reveals an "anti-Sq" system established between the mid latitudes and the equatorial region and opposes the normal Sq current vortex. However, the localization of the eastward current and consequently the position and the extent of the "anti-Sq" current vortex changes from one storm to another. Indeed, for a strong magnetic storm, the eastward current is well established at mid latitudes about 45° N and for a weak magnetic storm, the eastward current is established toward the high latitudes (about 60° N), near the Joule heating region, resulting in a large "anti-Sq" current cell. The latitudinal profile of the Ddyn disturbance as well as the magnetic disturbance DP2 generated by the mechanism of prompt penetration of the magnetospheric convection electric field in general, show a weak disturbance at the low latitudes with a substantial amplification at the magnetic equator. Due to the intensity of the storm, the magnitude of the DP2 appears higher than the Ddyn over the American and Asian sector contrary to the African sector.
Highlights
During magnetic storms, two main physical mechanisms of disturbance take place in the ionosphere, at the planetary scale: the direct penetration of magnetospheric convection electric field (Vasyliunas, 1970, 1972) and the ionospheric disturbance dynamo (Blanc and Richmond, 1980)
The disturbance of the magnetic field during the periods of observation would be due to the only mechanism of the ionospheric disturbance dynamo; in other words, the DP disturbance depicts the magnetic signature of the Ddyn disturbance
The Ddyn disturbance is maximum at the magnetic equator, probably due to the daytime significant Cowling conductivity effect at the equatorial electrojet altitude
Summary
Two main physical mechanisms of disturbance take place in the ionosphere, at the planetary scale: the direct penetration of magnetospheric convection electric field (Vasyliunas, 1970, 1972) and the ionospheric disturbance dynamo (Blanc and Richmond, 1980). This poleward electric field gives rise to a large eastward Hall current (J H =σH (E×B/B2)) and a poleward Pedersen current This physical process is called “ionospheric disturbance dynamo” by Blanc and Richmond (1980) and denoted by the symbol Ddyn (Le Huy and Amory-Mazaudier, 2005). There is a large divergence of the east-west currents at dawn and dusk which requires a closure of these currents on the highly conducting dayside through the adjacent latitudinal regions These currents achieve closure through two separate vortices: the polar vortex realized via the higher latitudes and the equatorial vortex realized via the lower latitudes where it constitutes a striking feature of the currents maps: a sort of “reversed Sq” current vortex flowing clockwise on the dayside with a focus close to noon at about 25◦ magnetic latitude. At the equatorial region, the westward currents flow is opposed to the normal eastward equatorial electrojet currents
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