Longitudinal modulation of electron and mass densities at middle and auroral latitudes: Effect of geomagnetic field strength

Abstract

In this study, the effect of a reduction in magnetic field strength on the longitudinal modulation of electron density (ΔNe) and mass density (Δρ) is investigated. We study conditions during the September equinox and June and December solstices at middle and auroral latitudes in both Northern and Southern Hemispheres. The Global Ionosphere‐Thermosphere Model was employed for the theoretical study. Simulations were performed with a realistic International Geomagnetic Reference Field (IGRF) model and an IGRF model reduced in strength by 50%. The reduction in field strength increased the longitudinal variations in ΔNe by 2–34% in the nighttime sector but reduced the variation by 7–20% in the daytime sector at midlatitudes in both hemispheres. Conversely, at auroral latitudes ΔNe was reduced by 2–32% at all local times. The changes during equinoxes are larger than those for the solstices. The differences with local time in the response of ΔNe to a reduction in magnetic field strength were mainly due to changes in the oxygen/molecular nitrogen (O/N2) ratio in the Northern Hemisphere, whereas the differences were due to the combined effects of vertical winds and changes in the O/N2 ratio in the Southern Hemisphere. Both vertical winds and horizontal trueE→×trueB→ convection eliminated ΔNe at high latitudes. Δρ got enhanced at both middle and auroral latitudes, which was related to the enhanced Joule heating effect when the magnetic field was reduced.

A planetary perspective on Earth’s space environment evolution

“…Both the simulation and observation show pretty similar solar cycle variations with time. In addition, both the simulation and observation also show long term trend variation independent of solar activity, which is a hot topic recently in the community (Laštovička et al, 2006; Yue et al, 2008; Wang et al, 2017). The model overestimates the h m F 2 especially over solar minimum (e.g.…”

Hemispheric Asymmetry of the Vertical Ion Drifts at Dawn Observed by DMSP

“…Accordingly, a general understanding of the asymmetric features of the auroral and subauroral V z in the GEO coordinates can help us to obtain a more complete physical picture about the asymmetric behavior of V z at high MLATs and further comprehension of the tightly coupled ionosphere‐thermosphere system. Meanwhile, note that the relatively larger magnetic inclination in the auroral and subauroral regions can lead to stronger effects of E × B drift and larger biases between the vertical and field‐aligned velocity (Deng & Ridley, ; Wang et al, ). Thus in this section, only a preliminary study is carried out to describe the general hemispheric difference in the auroral and subauroral V z .…”

“…Inside the polar cap, which is defined as the region at MLATs poleward of 77°N/S, V z can be taken as a good proxy for the field‐aligned drift. However, it should be noted that in the auroral and subauroral regions, there is a relatively larger bias between V z and field‐aligned velocity because of the effect of the magnetic inclination and declination (Deng & Ridley, ; Wang et al, ).…”

“…The larger upward ion drifts in the northern auroral zone are probably related to the larger auroral precipitation in the NH (Luan et al, 2010;Zhang et al, 2015), which is a possible driver of ion upwelling (e.g., Ogawa et al, 2003Ogawa et al, , 2008Wahlund et al, 1992). In addition, the relatively weaker magnetic field strength in the NH might also play a role because the reduced magnetic field strength could cause enhanced plasma convection and stronger Joule/frictional heating (Cnossen et al, 2011;Wang et al, 2017).…”

Simulating the Solar Wind‐Magnetosphere Interaction During the Matuyama‐Brunhes Paleomagnetic Reversal

“…Such a method of using a scaled dipole field is further used in other studies to examine the magnetosphere-ionosphere coupling and the dependences on the interplanetary magnetic field (IMF) (e.g., , Zieger, Vogt, Ridley, & Glassmeier, 2006. H. Wang et al (2017) found that reduced geomagnetic fields generally lead to an increase of the thermospheric mass density but a decrease of electron density at auroral latitudes. Some studies also investigated the effects of equatorial dipole magnetosphere (Zieger et al, 2004) or quadrupole configurations (Vogt et al, 2004(Vogt et al, , 2007 and suggested that high-energy particles in the MeV range are more likely to penetrate to about 𝐴𝐴 40 • altitude atmosphere during the reversal.…”