A statistical study of magnetospheric electron density using the Cluster spacecraft

• Published in: Journal of geophysical research. Space physics 2016-11, Vol.121 (11), p.11,042-11,062
• Main Authors: Sandhu, J. K., Yeoman, T. K., Fear, R. C., Dandouras, I.
• Format: Article
• Language: English
• Subjects: Cluster; Cluster spacecraft; Clusters; Density; Density distribution; Electric fields; Electron density; Electrons; Empirical models; Equator; field line dependence; Geomagnetic field; Geomagnetic fields; Geomagnetism; Geophysics; Magnetic equator; Magnetic fields; Magnetospheres; Magnetospheric electron density; mass density; Mathematical models; Onboard; Plasma; Plasmas (physics); Power law; Program verification (computers); Sciences of the Universe; Spacecraft; Spatial distribution
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA023397

Observations from the WHISPER (Waves of High frequency and Sounder for Probing of Electron density by Relaxation) instrument on board Cluster, for the interval spanning 2001–2012, are utilized to determine an empirical model describing the total electron density along closed geomagnetic field lines. The model, representing field lines in the region of 4.5≤L < 9.5, includes dependences on L and magnetic local time. Data verification tests ensured that the WHISPER data set provided unbiased measurements for low‐density regions, including comparisons with Plasma Electron and Current Experiment and Electric Field and Waves observations. The model was determined by modeling variations in the electron density along the field lines, which is observed to follow a power law distribution along the geomagnetic field at high latitudes, with power law index values ranging from approximately 0.0 to 1.2. However, a localized peak in electron density close to the magnetic equator is observed, which is described using a Gaussian peak function, with the electron density peak ranging as high as 10 cm−3 above the background power law dependence. The resulting model illustrates some key features of the electron density spatial distribution. The role of the number density distribution, represented by the empirical electron density model, in determining the total plasma mass density is also explored. By combining the empirical electron density model with an empirical average ion mass model, the total plasma mass density distribution is inferred, which includes contributions of both the number density and ion composition of the plasma in the region. Key Points WHISPER/Cluster observations used to determine empirical electron density model Observed enhancement in total electron density field line distribution, localized to equator Empirical models describing number density and ion composition used to determine empirical mass density model