On the Balance Between Plasma and Magnetic Pressure Across Equatorial Plasma Depletions

Abstract

In magnetized plasmas such as the ionosphere, electric currents develop in regions of strong density gradients to balance the resulting plasma pressure gradients. These currents, usually known as diamagnetic currents decrease the magnetic pressure where the plasma pressure increases, and vice versa. In the low‐latitude ionosphere, equatorial plasma depletions (EPDs) are well known for their steep plasma density gradients and adverse effect on radio wave propagation. In this paper, we use continuous measurements of the magnetic field and electron density from the European Space Agency's Swarm constellation mission to assess the balance between plasma and magnetic pressure across large‐scale EPDs. The analysis is based on the magnetic fluctuations related to diamagnetic currents flowing at the edges of EPDs. This study shows that most of the EPDs detected by Swarm present a decrease of the plasma pressure relative to the ambient plasma. However, EPDs with high plasma pressure are also identified mainly in the vicinity of the South Atlantic magnetic anomaly. From the electron density measurements, we deduce that such an increase in plasma pressure within EPDs might be possible by temperatures inside the EPD as high as twice the temperature of the ambient plasma. Due to the distinct location of the high‐pressure EPDs, we suggest that a possible heating mechanism might be due to precipitation of particle from the radiation belts. This finding corresponds to the first observational evidence of plasma pressure enhancements in regions of depleted plasma density in the ionosphere.

Ionospheric Plasma Density Oscillation Related to EMIC Pc1 Waves

“…According to Stolle et al (2006) and Laundal et al (2019), diamagnetic effects of ionospheric irregularities generally result in a 180° phase difference between plasma density and compressional magnetic residuals. On the other hand, a minority of irregularities with exceptionally high‐temperature changes may lead to an in‐phase relationship (Rodríguez‐Zuluaga et al, 2019). Hence, we cannot entirely discard the possibility that the diamagnetic effect of preexisting plasma irregularities (even without actual Pc1 waves) may have caused the nearly in‐phase relationship between plasma density undulations and compressional Pc1 (Figure 1f) on 4 November 2018.…”

Global‐Scale Observations of the Equatorial Ionization Anomaly

“…Consequently, the occurrence of ionospheric irregularities are a critical challenge for efforts to predict space weather in the ionosphere. The climatology has been studied using previous satellite observations (e.g., Burke et al, , Burke et al, ; Su et al, ; Comberiate & Paxton, ; Zhan et al, ; Rodríguez‐Zuluaga et al, ), and high‐resolution numerical models have succeeded in generating consistent ionospheric structures (e.g., Huba et al, ; Retterer, ). The observational history of the phenomenon and recent efforts to understand its causation have been reviewed by, for example, Kelly et al () and Balan et al ().…”

Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers: CryoSat-2 and GRACE-FO

“…Also, there are other ionospheric current systems with weaker magnetic effect than the two mentioned above. To name a few, we have solar quiet (Sq) currents flowing in the ionospheric E-layer (Yamazaki and Maute 2017), inter-hemispheric field-aligned currents (IHFACs) connecting the two Sq systems in respective hemispheres (Shinbori et al 2017;Lühr et al 2015Lühr et al , 2019, gravity-driven horizontal currents (Lühr and Maus 2006;Maute and Richmond 2017), pressure-driven currents which counter-balance plasma density inhomogeneity (Lühr et al 2003;Stolle et al 2006;Alken et al 2016;Maute and Richmond 2017;Rodríguez-Zuluaga et al 2019;Laundal et al 2019), wind-driven dynamo currents flowing vertically in the ionospheric F-layer (Lühr and Maus 2006), horizontal currents across the polar cap closing net auroral FACs (Lühr and Zhou 2020, and references therein), and low-/mid-latitude small-scale FACs resulting from a divergence of background currents by ionospheric irregularities (Park et al 2009;Rodríguez-Zuluaga et al 2017;Yin et al 2019). There also exist magneto-hydrodynamic (MHD) waves propagating in the ionosphere and accompanying currents, such as Pc3 (Heilig and Sutcliffe 2016) and Pc1 pulsations (Kim et al 2018;Gou et al 2020).…”