The 2.29 GHz S band carrier signals of the two Helios spacecraft are used to probe the magnetic and density structures of the solar corona inside 0.05 AU. In this paper we analyze the observed fluctuations of the electron content and Faraday rotation. A simple statistical ray analysis is employed. We conclude that (1) the observed Faraday rotation fluctuations cannot be solely due to electron density fluctuations in the corona unless the coronal magnetic field is some 5 times stronger than suggested by current estimates, and (2) the observed Faraday rotation fluctuations are consistent with the hypothesis that the sun radiates Alfvén waves with sufficient energies to heat and accelerate high‐speed solar wind streams.

Coronal Faraday rotation of the linearly polarized carrier signals of the HELIOS spacecraft was recorded during the regularly occurring solar occultations over almost a complete solar cycle from 1975 to 1984. These measurements are used to determine the average strength and radial variation of the coronal magnetic field at solar minimum at solar distances from 3-10 solar radii, i.e., the range over which the complex fields at the coronal base are transformed into the interplanetary spiral. The mean coronal magnetic field in 1975-1976 was found to decrease with radial distance according to r-=, where ~ = 2.7 + 0.2. The mean field magnitude was 1.0 + 0.5 x 10-s tesla at a nominal solar distance of 5 solar radii. Possibly higher magnetic field strengths were indicated at solar maximum, but a lack of data prevented a statistical determination of the mean coronal field during this epoch.

A concerted search for coronal transients was conducted with the 'Solwind' coronagraph during the solar occultations of the two Helios spacecraft in October/November 1979. The polarization angle and bandwidth of the linearly polarized S-band downlink signal were monitored at the three 64-m tracking stations of the NASA Deep Space Network to determine coronal Faraday rotation and spectral broadening. A one-to-one correspondence could be established between abrupt disturbances in the two signal parameters and the passage of a white-light transient through the signal ray path from spacecraft to Earth. The white-light morphology and the additional information provided by the radio sounding coverage are presented for each of the five distinct events recorded. Although no specific example could be observed in sufficient detail in both white light and Faraday rotation to derive the small-scale magnetic structure, some qualitative descriptions of the orientation and rough estimates of the magnitude of the transient magnetic field could be made.

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A set of significant S band radio occultation measurements was obtained with Mariner 9 during May and June of 1972, for the first time yielding extensive occultation data on the north and south polar regions. The daytime temperature profiles, representative of a clear atmosphere, exhibit gradients (averaging −2.3°K/km) far smaller than those expected under conditions of radiative‐convective balance. The measured gradients are in good agreement with those computed for Stone's radiative dynamical models. The near‐surface temperatures (180°–190°K) measured in the Martian spring daytime on the north polar cap indicate that it may, at least in part, consist of water ice. Temperatures in the south polar area, measured in nighttime, were low enough for condensation of carbon dioxide to take place. Measurements of the height of the daytime ionosphere at solar zenith angles greater than 72° are lower than the expected heights of the ionization peak, possibly indicating about 25% cooling of the lower atmosphere between November and December of 1971 and May and June of 1972. Planetary radii obtained at latitudes ranging from +86° to −80° indicate a pronounced north‐south asymmetry. The south polar region is higher than the north polar area by an average of about 3.4 km; the entire southern hemisphere is 3–4 km higher than the northern hemisphere. A measurement was obtained near the summit of Middle Spot (Pavonis Lacus) showing it to rise about 13.5 km above the surounding terrain.