Ionospheric wind dynamo theory: A review.

Abstract

The current state of ionospheric wind dynamo theory is reviewed. Observational and theoretical advances in recent years have permitted more accurate models of the dynamo mechanism to be presented than previously, which have lent further credence to the validity of dynamo theory as the main explanation for quiet-day ionospheric electric fields and currents at middle and low latitudes. The diurnal component of the wind in the upper E region and lower F region appears to be primarily responsible for average quiet-day currents, although other wind components give significant contributions. Observationally, there is a need for better spatial and temporal coverage of wind and electric field data. Theoretically, there is a need for further consideration of the mutual dynamic coupling among winds, conductivities, electric fields, and electric currents, and for better modeling of nighttime conditions.

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Geomagnetic disturbances associated with storms and substorms are typically several hundreds of nano teslas on the surface, which can easily mask underlying Sq signals. Despite the small amplitude, studies on Sq have been important for understanding the ionospheric electrodynamics (Richmond 1979(Richmond , 1995b and its coupling to the magnetosphere and lower atmosphere (Wagner et al 1980;Richmond 1995b); for determining a base level for geomagnetic indices (Mayaud 1980;Love and Gannon 2009;Gjerloev 2012); for monitoring solar radiation activity (Svalgaard and Cliver 2007;Svalgaard 2016); and for estimating electrical conductivity within the Earth (Campbell and Schiffmacher 1988a;Campbell et al 1998;Okeke and Obiora 2016).…”

Long-term behavior of annual and semi-annual S q variations

“…The principal source of the quiet daily variation of the geomagnetic field (S q variation) is the electric current flowing in the ionospheric E region (90-150 km), which is generated by the movement of conducting air across the Earth's main field (Richmond, 1979(Richmond, , 1989(Richmond, , 1998. Although the ionospheric current can induce secondary currents in the conducting earth, the secondary current does not make any difference to the solar-activity dependence of the S q field because the intensity of the secondary current proportionally increases with increasing ionospheric current intensity (Malin et al, 1975).…”

F region drift observations from Athens Digisonde

“…This field at middle and low latitudes on magnetically quiet conditions is believed to be produced mainly by the dynamo action of thermospheric winds [e.g., Richmond, 1979] and causes the ionospheric and plasmaspheric plasmas to drift perpendicular to the geomagnetic field [Richmond, 1976]. Richmond et al [1980] in an empirical study used seasonally averaged quiet day (Kp < 3) F region ionospheric E Â B drift observations (horizontal drift vector components) from the Millstone Hill, St. Santin, Arecibo, and Jicamarca incoherent scatter radars to produce a model of the middle-and low-latitude electric field for solar minimum conditions.…”