Abstract
AbstractIn situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP‐B covering all MLTs are used to study the small‐scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes >10% from background density and with time‐scales less than 30‐min are investigated here as the small‐scale density irregularities. The statistical survey of the density irregularities is carried out using nearly 2 years of density data obtained from RBSP‐B and 4 months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L‐shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: (1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to coexist with the hot plasma sheet population. (2) During quiet periods, the plasma waves in the whistler‐mode frequency range are found to be modulated by the small‐scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.
Highlights
The plasmasphere is the innermost region of the Earth’s magnetosphere, which is filled with cold (low energy ∼1–10 electron volt and dense (10–104 cm−3)) plasma of ionospheric origin trapped to the Earth’s magnetic field, forming a thermal plasma cloud encircling the Earth (Darrouzet et al, 2009b; Lemaire et al, 1998)
Our observations suggest that different source mechanisms are responsible for the generation of density structures at different magnetic local time (MLT) and geomagnetic conditions
The present study investigates the density irregularities in the plasmasphere and its outer regions in detail by probing the electron density observations from Arase in the nightside and RBSP-B from all MLT sectors
Summary
The plasmasphere is the innermost region of the Earth’s magnetosphere, which is filled with cold (low energy ∼1–10 electron volt (eV) and dense (10–104 cm−3)) plasma of ionospheric origin trapped to the Earth’s magnetic field, forming a thermal plasma cloud encircling the Earth (Darrouzet et al, 2009b; Lemaire et al, 1998). One of the earliest in situ observations of the cold plasma density was made by OGO 5 (Chappell et al, 1970), EXOS-B (Oya & Ono, 1987), CRRES (LeDocq et al, 1994), and Los Alamos National Laboratory (Moldwin et al, 1995) satellite missions These observations revealed the existence of density irregularities near the plasmapause and the outer regions of the plasmasphere. This paper presents the statistical survey of small-scale density irregularities in the plasmasphere and near the plasmapause by investigating the electron density profiles from Van Allen Probes and Arase satellites in the equatorial and off-equatorial latitudes, respectively. The present study investigates the density irregularities inside and outside the plasmasphere using data from two inner magnetospheric satellite missions, Exploration of energization and Radiation in Geospace (ERG, known as Arase; Miyoshi et al, 2018c) and Van Allen Probes The mGSE system for RBSP will be about 20° off the GSE system
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