Voyager 2 solar plasma and magnetic field spectral analysis for intermediate data sparsity

Kavli Affiliate: John D. Richardson

| First 5 Authors: Luca Gallana, Federico Fraternale, Michele Iovieno, Sophie M. Fosson, Enrico Magli

| Summary:

The Voyager probes are the furthest, still active, spacecraft ever launched
from Earth. During their 38-year trip, they have collected data regarding solar
wind properties (such as the plasma velocity and magnetic field intensity).
Unfortunately, a complete time evolution of the measured physical quantities is
not available. The time series contains many gaps which increase in frequency
and duration at larger distances. The aim of this work is to perform a spectral
and statistical analysis of the solar wind plasma velocity and magnetic field
using Voyager 2 data measured in 1979, when the gaps/signal ratio is of order
of unity. This analysis is achieved using four different data reconstruction
techniques: averages on linearly interpolated subsets, correlation of linearly
interpolated data, compressed sensing spectral estimation, and maximum
likelihood data reconstruction. With five frequency decades, the spectra we
obtained have the largest frequency range ever computed at 5 astronomical units
from the Sun; spectral exponents have been determined for all the components of
the velocity and magnetic field fluctuations. Void analysis is also useful in
recovering other spectral properties such as integral scales (see for instance
Table 4) and, if the confidence level of the measurements is sufficiently high,
the decay variation in the small scale range due, for instance, to dissipative

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