Statistical Study on Small‐Scale (≤1,000 km) Density Irregularities in the Inner Magnetosphere

Abstract

In the Earth's inner magnetosphere, which generally lies within L-shell = 7, the cold plasma population (∼1 eV) is divided into three spatial regions: the plasmasphere, the plasma trough, and the plasmasphere boundary layer (PBL). The plasmasphere is a torus-like, high-density (≥50 cc) region around the Earth, while the surrounding plasma trough is tenuous (∼ 1 cc). Between the two regions is the PBL (or the plasmapause), with large density gradients and often accompanied by significant density structures (Carpenter & Lemaire, 2004). The location of PBL, which is controlled by global convection (Chappell, 1972;Nishida, 1966), is highly dynamic in response to geomagnetic activities: it varies from L = 2-3 due to erosion during active conditions (Carpenter & Anderson, 1992;Moldwin et al., 2002) to L ∼ 7 due to refilling during prolonged quiet conditions (Kwon et al., 2015). One large-scale (∼1 R E ) structure near the PBL is the plasmaspheric plume, which is peeled away from the plasmasphere by enhanced convection fields (Chen & Wolf, 1972;Goldstein et al., 2004). Other medium-density to large-density structures (>0.1 R E ) include the notches, channels, shoulders, fingers, and crenulations observed in EUV (extreme ultraviolet) images (Darrouzet et al., 2009;Spasojević et al., 2003).Small-scale density irregularities have cross-field scales ranging from ∼10 m to ∼1,000 km and occur in all parts of the inner magnetosphere (Sonwalkar, 2006). They have been extensively observed in the PBL (Décréau et al., 2005) and plume regions (Borovsky & Denton, 2008;Goldstein et al., 2004). Small-scale density irregularities are generally thought to be field-aligned structures and thus are referred to as field-aligned irregularities

Filtering of Magnetosonic Waves by Mesoscale Plasmaspheric Density Interfaces

“…Because of the rotation, erosion, and filling processes, the plasmasphere exhibits diverse structures and boundaries over a broad range of radial distances and magnetic local times (Borovsky & Denton, 2008; Darrouzet et al., 2009; Goldstein et al., 2004). Meanwhile, these boundaries are rich in density irregularities of smaller scales (Carpenter & Lemaire, 1997; Carpenter et al., 2002; Gu et al., 2022; Thomas et al., 2021; Wu, Su, Goldstein, et al., 2022). The incidence of magnetosonic waves toward density interfaces should frequently occur and the associated transmission and reflection processes would eventually affect the global distribution of magnetosonic waves.…”

Long Lifetime Hiss Rays in the Disturbed Plasmasphere

“…In the low‐altitude ionosphere, the gradient drift instability (Gondarenko & Guzdar, 2004; Keskinen et al., 2004; Rathod et al., 2021) and temperature gradient instability (Greenwald et al., 2006; Hudson & Kelley, 1976) can produce density fluctuations on a scale from several to tens of km, which may further cascade into fluctuations of 10 m scale (Eltrass et al., 2016; Heine et al., 2017; Nishimura et al., 2021). When mapped from the ionosphere to the magnetosphere, these density fluctuations appear as the field‐aligned density ducts with cross‐field sizes of ∼0.1–100 km (Gu et al., 2022; Nishimura et al., 2022). Other than the ionospheric instabilities, the local interchange instability and turbulent flow could also produce the small‐scale density irregularities in the plasmaspheric plume (Borovsky & Denton, 2008; Huang et al., 1990; Rodger et al., 1998; Sazykin et al., 2002).…”

An Automatic Method for Detection and Naive Classification of the Martian Ionospheric Irregularities

“…To precisely extract the O 2 + density perturbations, the proper upper and lower envelopes are first estimated based on a so-called rolling-barrel algorithm (Cao et al, 2023;Gu et al, 2022;Pradipta et al, 2015;Sternberg, 1983).…”

“…To precisely extract the O 2 + density perturbations, the proper upper and lower envelopes are first estimated based on a so‐called rolling‐barrel algorithm (Cao et al., 2023; Gu et al., 2022; Pradipta et al., 2015; Sternberg, 1983). The principal idea of this algorithm is that by imagining the data sequence as rough terrain, the contact points of a rolling cylindrical barrel on the terrain could then be determined.…”