The diamagnetic effect of the equatorial Appleton anomaly: Its characteristics and impact on geomagnetic field modeling

Abstract

[1] The diamagnetic effect generally reduces the magnetic field inside a plasma. Its importance is appreciated in regions like the magnetosphere and the solar wind. In the ionosphere, depletions of the geomagnetic field have up to now been considered negligible. The CHAMP satellite provides for the first time the combination of highresolution magnetic field measurements and plasma density observations on the same spacecraft in low-Earth orbit. We show the typical distribution of electron density at the altitude of about 430 km for various local times. Particularly prominent features are the density enhancements north and south of the dip equator. As expected, the magnetic field intensity is depressed in the crest region by an amount of more than 5 nT. The diamagnetic effect is strongest from sunset to midnight and thus causes errors in global geomagnetic field models which are usually computed from data sampled at all night-time hours.

NOAA/NGDC candidate models for the 11th generation International Geomagnetic Reference Field and the concurrent release of the 6th generation Pomme magnetic model

“…3. The signature of plasma pressure gradient currents is subtracted using the correction for the "diamagnetic effect", as proposed by Lühr et al (2003), making use of actual electron density and temperature measurements by CHAMP. 4.…”

Neutral density depletions associated with equatorial plasma bubbles as observed by the CHAMP satellite

“…After the 76 geomagnetic contributions from the Earth's core, crust, and mag-77 netosphere (hereafter called 'mean field') are subtracted from the 78 B-field vector, the residual B-field strength (or equivalently the 79 component parallel to the mean field) reflects ionospheric plasma den-80 sity structures (Lühr et al, 2003;Stolle et al, 2006). In this study we will 81 only deal with the residual B-field.…”

“…The obtained neutral density reading has a resolution of 2 × 10 −14 kg/m 3 at are available at a time rate of 1 second (Lühr et al, 2003). After the 76 geomagnetic contributions from the Earth's core, crust, and mag-77 netosphere (hereafter called 'mean field') are subtracted from the 78 B-field vector, the residual B-field strength (or equivalently the 79 component parallel to the mean field) reflects ionospheric plasma den-80 sity structures (Lühr et al, 2003;Stolle et al, 2006).…”

Mid-latitude solar eclipses and their influence on ionospheric current systems

“…Zonal winds at low latitudes cause a charge separation in vertical direction and set up a current system as illustrated in Fig. 9 (Heelis, 2004;Lühr and Maus, 2006). In our case we need an eastward wind to drive the observed upward current.…”

“…7, as a key element for the interpretation of the whole current system. Such a current system is indicative of the action of the F-region dynamo (Risbeth, 1971;Lühr and Maus, 2006). Zonal winds at low latitudes cause a charge separation in vertical direction and set up a current system as illustrated in Fig.…”