Some results of cislunar plasma research

The main results of plasma cislunar investigations, carried out during Luna-19 and Luna-22 spacecraft flights by means of dual frequency dispersion interferrometry, are briefly outlined. It is shown that a thin layer of plasma, with a height of several tens of kilometers and a maximum concentration of the order 1,000 electrons/cu cm exists above the solar illuminated lunar surface. A physical model of the formation and existence of such a plasma in cislunar space is proposed, taking into account the influence of local magnetic areas on the moon

The nighttime ionosphere of Mars from Mars-4 and Mars-5 radio occultation dual-frequency measurements

Dual frequency radio sounding of the Martian nighttime ionosphere was carried out during the exits from behind the planet of the Mars-4 spacecraft on February 2, 1974 and the Mars-5 spacecraft on February 18, 1974. In these experiments, the spacecraft transmitter emitted two coherent monochromatic signals in decimeter and centimeter wavelength ranges. At the Earth receiving station, the reduced phase difference (or frequencies) of these signals was measured. The nighttime ionosphere of Mars measured in both cases had a peak electron density of approximately 5 X 1,000/cu cm at an altitude of 110 to 130 km. At the times of spacecraft exit, the solar zenith angles at the point of occultation were 127 deg and 106 deg, respectively. The height profiles of electron concentration were obtained assuming spherical symmetry of the Martian ionosphere

Observations of Corotating Solar Wind Structures at Radio Sounding by Signals of the Rosetta and Mars Express Spacecraft

In the implementation of the space projects Rosetta and Mars Express, a large-scale series of experiments has been carried out on radio sounding circumsolar plasma by decimeter (S-band) and centimeter (X-band) signals of the Rosetta comet probe (from October 3 to October 31, 2010) and the Mars Express satellite of Mars (from December 25, 2010 to March 27, 2011). It was found that in the phase of ingress the spacecraft behind the Sun, the intensity of the frequency fluctuations increases in accordance with a power function whose argument is the solar offset distance of radio ray path, and when the spacecraft is removed from the Sun (the egress phase), frequency fluctuations are reduced. Periodic strong increases in the fluctuation level, exceeding by a factor of 3-12 the background values of this value determined by the regular radial dependences, are imposed on the regular dependences. It was found that increasing the fluctuations of radio waves alternates with the periodicity m x T or n x T, where m = 1/2, n = 1,.nd T is the synodic period of the Sun's rotation (T approximate to 27 days). It was shown that the corotating structures associated with the interaction regions of different speed fluxes are formed in the area of solar wind acceleration and at distances of 6-20 solar radii already have a quasi-stationary character

Frequency fluctuations in the solar corona investigated with radio sounding experiments on the spacecraft ROSETTA and MARS EXPRESS in 2010/2011

Coronal radio-sounding experiments were carried out using two-way coherent dual-frequency carrier signals of the ESA spacecraft ROSETTA in 2010 and MARS EXPRESS in 2010/2011. Differential frequency measurements recorded at both NASA and ESA tracking stations (sample rate: 1 Hz) are analyzed in this paper. Spectral analysis of the S-band, X-band, and differential frequency records has shown that the r.m.s. frequency fluctuation of each signal can be described by a radial power-law function of the form sigma(i) = A(i){R/R-circle dot)(-beta i), where i = s, x, sx. The ratio of the coefficients A(s) and A(x) differs from the expected theoretical value A(s)/A(x) = f(s)/f(x). This occurs because the X-band fluctuations underlie two-way propagation conditions while the S-band fluctuations are essentially the product of a one-way propagation experiment. The intensity of the frequency fluctuations decreases sharply at high heliolatitudes. The asymmetry of the frequency fluctuation intensity between ingress and egress is exploited to determine the solar wind speed at small heliocentric distances. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved

Coronal Radio Occultation Experiments with the Helios Solar Probes: Correlation/Spectral Analysis of Faraday Rotation Fluctuations

The coronal Faraday rotation (FR) experiments using the linearly polarized signals of the Helios-1 and Helios-2 interplanetary probes remain a unique investigation of the magnetic field of the solar corona and its aperiodic and quasi-periodic variations. The unexpectedly long lifetime of these spacecraft (1974 -aEuro parts per thousand 1986) enabled studies from very deep solar-activity minimum (1975 -aEuro parts per thousand 1976) into the strong activity maximum (1979). Important experimental data were also obtained for the rising (1977 -aEuro parts per thousand 1978) and declining (1980 -aEuro parts per thousand 1984) branches of the solar-activity cycle. Previous publications have presented results of the initial experimental data only for coronal-sounding experiments performed during individual solar-conjunction opportunities. This report is a more detailed analysis of the Helios FR measurements for the entire period 1975 -aEuro parts per thousand 1984. Radial profiles of the FR fluctuation (FRF) intensity recorded during the deepest solar-activity minimum in 1975 -aEuro parts per thousand 1976 are shown to differ distinctly from those during the strong solar-activity maximum in 1979. In particular, the decrease of the FRF intensity with solar-offset distance is substantially steeper in 1979 than in 1975/1976. In all cases, however, the FR data reveal quasi-periodic wave-like fluctuations in addition to the random background with a power-law spectrum. The dominant period of these fluctuations, recorded during 35 % of the total measurement time, is found to be close to five minutes. Large-scale FR variations at considerably longer periods (1.1 -aEuro parts per thousand 2.7 hours) were observed during 20 % of the measurement time. Knowing the intrinsic motion of the radio ray path from spacecraft to Earth and making a reasonable assumption about the solar-wind velocity, FRF observations at widely spaced ground stations have been used to estimate the velocity of coronal Alfv,n waves. The velocity values range between 290 and 550 km s(-1) at heliocentric distances between 3.5 and 4.5 R-aS (TM) and are marginally lower (150 -aEuro parts per thousand 450 km s(-1)) at distances between 5.5 and 6.5 R-aS (TM). Occasional FR variations with a period near 160 minutes and harmonics with periods 60, 30, and 20 minutes were also observed

Faraday-rotation fluctuations from radio-sounding measurements of the circumsolar plasma using polarized signals from the HELIOS-1 and HELIOS-2 space probes

Fluctuations in the Faraday rotation of the plane of polarization of S-band (2.3 GHz) radio signals transmitted through the solar corona by the HELIOS-1 AND HELIOS-2 space probes are analyzed. Simultaneous measurements of the Faraday-rotation fluctuations at the Goldstone and Canberra stations have yielded estimates of the velocity of perturbations of the magnetic field in the circumsolar plasma at heliocentric distances of three to six solar radii. The velocity of these perturbations is a combination of the Alfv,n and solar-wind speeds. Temporal spectra of the Faraday-rotation fluctuations are obtained based on a large volume of observational data obtained in various years in four cycles of radio-sounding experiments. Filtration of the input data using spectral, correlation, and wavelet analyses shows that trains of quasi-periodic oscillations of the magnetic field with various amplitudes and periods from 2 to 160 min are regularly present in the Faraday-rotation fluctuations. This quasi-periodic character of these perturbations supports their connection with Alfv,n waves propagating in the circumsolar plasma

Two-Way Frequency Fluctuations Observed During Coronal Radio Sounding Experiments

Coronal radio-sounding experiments were carried out using two-way coherent dual-frequency carrier signals of the ESA spacecraft Rosetta (ROS) in 2006. Frequency measurements recorded at both NASA and ESA tracking stations (sample rate: 1 Hz) are analyzed in this work. Spectral analysis of the S-band, X-band, and differential frequency records has shown that the mean frequency fluctuation of each signal can be described by a radial power-law function of the form sigma (i) =A (i) (R/R-aS (TM))(-mi) , where i=x,s,sx. The ratio of the coefficients A (s) and A (x) is not the expected theoretical value A (s)/A (x)=f (s)/f (x). This occurs because the X-band fluctuations underlie a two-way propagation mode while the S-band fluctuations are essentially the product of a one-way propagation experiment. Results are compared with similar, but not identical, two-way radio propagation experiments performed during the 1991 solar conjunction of the Ulysses spacecraft

Turbulence Regimes of the Solar Wind in the Region of its Acceleration and Initial Stage of Supersonic Motion

Abstract. Coronal radio sounding experiments were carried out during the solar conjunctions of the spacecraft Ulysses and Galileo, providing information on the solar wind plasma over a wide range of heliocentric distances and heliolatitudes on both East and West limbs of the Sun. An important component of these investigations is to identify the turbulence regimes of the solar wind in its acceleration and initial supersonic regions. This work concentrates on the variation of the spectral index of the temporal frequency fluctuation spectrum α f . The analysis leads to the following preliminary conclusions: (1) At low heliolatitudes the turbulence becomes 'developed', with α f reaching the Kolmogorov value of 2/3, at distances beyond 20 R ¬ ; (2) At high heliolatitudes (poleward of 65 AE ) the solar wind turbulence remains undeveloped out to distances of at least 30 R ¬ ; (3) At distances close to the Sun (less than 7 R ¬ ) the spectrum sometimes becomes a double power-law with small spectral index α f ³ 0.03-0.11 at low fluctuation frequencies (ν 0.02 Hz), but a sharp decrease (α f 1.2) in the fluctuation regime beyond the break frequency