Magnetospheric electron density model inferred from Polar plasma wave data

• Published in: Journal of Geophysical Research. A. Space Physics 2002-11, Vol.107 (A11), p.SMP 25-1-SMP 25-8
• Main Authors: Denton, R. E., Goldstein, J., Menietti, J. D., Young, S. L.
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; electron density; Exact sciences and technology; External geophysics; field line dependence; Physics of the magnetosphere; Plasma motion, convection, circulation. Plasma instabilities; plasmasphere
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2001JA009136

Observations of the electron density ne based on measurement of the upper hybrid resonance frequency by the Polar spacecraft Plasma Wave Instrument (PWI) are available for March 1996 to September 1997, during which time the Polar orbit sampled all magnetic local time (MLT) values three times. Using the entire data set, we bin the ne values with respect to maximum field line radius LRE and radius R to generate an average density model for 3.5 ≤ L ≤ 7.8 and 3RE ≤ R ≤ LRE. While our method does not assume any particular functional form for the density dependence along field lines, we find that the dependence can be roughly described by the power law form ne = ne0 (LRE/R)α with α having on average a value 0.2–0.9 in the plasmasphere (inner L region, 3.5 ≤ L ≤ 5.5), and a value 1.6–2.1 in the plasmatrough (outer L region, L ≥ 7). For instance, α = 0.8 ± 1.2 at L = 4.4 and α = 2.1 ± 1.4 at L = 7 (where the errors noted are overestimates). This result is similar to a previous result based on the Polar PWI data but using a different method. Alternately, the scale length for field line variation of density Lα ≡ (LRE)/ = 5.5 ± 4.1RE across the entire region 4.4 ≤ L ≤ 7.8 (where the error noted is an overestimate). The data is also separated according to MLT, and it is shown that in the dawn sector the density is depleted and the radial dependence is steeper (larger α) than for other MLT sectors. A similar result holds when the averaged Kp value is large (>2).