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A spherical Fabry-Perot interferometer on Ogo 6 (launched June 5, 1969) gives the profile of the 6300-A oxygen line in the dayglow at different altitudes between 200 and 320 km. The temperature of the neutral components of the atmosphere is deduced from these measurements with an accuracy of ±65°K. The results presented in this paper correspond to the storm period September 25 to October 5, 1969. During this period a severe geomagnetic storm occurred. The temperature measurements show a very strong effect in the two polar regions, while the equatorial regions present a smooth temperature variation.

International audience; The University of Paris experiment, operating on board the Oso 5 spacecraft since January 22, 1969, observes the solar Lyman α line integrated over the whole solar disk. The hydrogen and deuterium resonance cells yield information about the solar flux at the center of the line and on the blue wing. The center of the solar line as observed from the spacecraft is strongly absorbed by the earth's geocorona. Therefore the hydrogen resonance data contain solar, as well as geocoronal, information. Comparison of the data with sophisticated exospheric models gives the following principal results: (1) A high correlation (0.87 coefficient) exists between the total Lyman α line flux and the center line flux. A 30% variation in the total flux corresponds to a 47% variation in the central flux. The average fluxes over 1969 and 1970 are 3 × 1011 ph cm−2 sec−1 total flux and 5 × 1011 ph cm−2 sec−1 A−1 central flux. (2) The absolute value of the hydrogen density at 500-km altitude (independent of the experiment's calibration) is of the order of 5 × 104 atoms cm−3 on the day side and 9 × 104 atoms cm−3 on the night side. (3) The earth's hydrogen exobase is controlled by the zero net ballistic flux condition (i.e., the outgoing ballistic flux is everywhere equal to the incoming ballistic flux). This is why an average ratio of 1.7 was found between the maximum and minimum densities at the exobase. A discrepancy appeared between the absolute values of the hydrogen density measured by this experiment and the corresponding absolute values predicted by the model of G. Kockarts and M. Nicolet (1963). In order to fit our data, the values of the model should be increased to the following hydrogen densities at an altitude of 100 km: 2.3 × 107 atoms cm−3 for low solar activity (Zurich number Rz ∼ 60); 2.5 × 107 atoms cm−3 for mean solar activity (Rz ∼ 120); and 4 × 107 atoms cm−3 for high solar activity (Rz ∼ 180).

In view of the limitation on length set by the cost of producing the IAU Reports, the present report can only be a selection of the most important advances during the past three years and not a complete review of the field.Attempting to pick out a few points of interest, since the last report improvements have been made in recording solar X-ray spectra and in high spatial resolution imaging; the OSO satellite programme continues to produce valuable data. The eclipse experiments planned for March 1970 will, if successful, provide a considerable amount of new information. The solar iron abundance is still a subject of interest in view of the revision of oscillator strengths used in the photospheric analyses. Further interplanetary observations have shown that the general nature of the solar wind at the Earth does not depend on the phase of the solar activity cycle, and have revealed large increases in the abundance of helium in the solar wind following solar flares.

PHOTOMETRIC observations can be used to measure the velocity of the Solar System through an interstellar medium and also provide an accurate method of measuring the temperature of that medium, provided that a very narrow filter is used in order to determine the emission linewidth. We present here the results obtained using a hydrogen absorption cell in conjunction with a Lyman-α photometer contained in the Soviet scientific spacecraft Prognoz-5 which was launched in November 1976. We use only the Lα results to measure the temperature of the interplanetary–interstellar hydrogen. The high result we obtained indicates that the Solar System may be moving through an intercloud medium heated by cosmic- or soft X-rays.

Thermal structure measurements obtained by the two VEGA balloons show the Venus middle cloud layer to be generally adiabatic. Temperatures measured by the two balloons at locations roughly symmetric about the equator differed by about 6.5 kelvins at a given pressure. The VEGA-2 temperatures were about 2.5 kelvins cooler and those of VEGA-1 about 4 kelvins warmer than temperatures measured by the Pioneer Venus Large Probe at these levels. Data taken by the VEGA-2 lander as it passed through the middle cloud agreed with those of the VEGA-2 balloon. Study of individual frames of the balloon data suggests the presence of multiple discrete air masses that are internally adiabatic but lie on slightly different adiabats. These adiabats, for a given balloon, can differ in temperature by as much as 1 kelvin at a given pressure.

A global array of 20 radio observatories was used to measure the three-dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the Venus atmosphere near Venus midnight by the VEGA spacecraft on 11 and 15 June 1985. Initial analysis of only radial velocities indicates that each balloon was blown westward about 11,500 kilometers (8,000 kilometers on the night side) by zonal winds with a mean speed of about 70 meters per second. Excursions of the data from a model of constant zonal velocity were generally less than 3 meters per second; however, a much larger variation was evident near the end of the flight of the second balloon. Consistent systematic trends in the residuals for both balloons indicate the possibility of a solar-fixed atmospheric feature. Rapid variations in balloon velocity were often detected within a single transmission (330 seconds); however, they may represent not only atmospheric motions but also self-induced aerodynamic motions of the balloon.

International audience; DURING the exploration of the planet Venus by the Soviet space probe Venera 9, we measured the quantity of hydrogen in the upper atmosphere and its temperature through the optical observation of far UV atmospheric emission. The temperature at the altitude of 250 km (the upper boundary of the atmosphere) was found to vary from 500 K on the dayside to 200 K on the nightside. This variation is compatible with our current knowledge of the heating of upper atmosphere by the solar radiation. It is shown here that this variation, which is larger than on Earth, induces an exospheric transport (out of the atmosphere) of hydrogen from the dayside to the nightside. As an indirect consequence, this transport allows the existence of a large quantity of atomic oxygen in the upper atmosphere, a feature which was still controversial.

It is proposed to base the scenario of the exploration of Mars on air-borne vehicles using solar power for mobility. A two-balloon option is presented. One of the balloons, closed, non superpressurized, filled with helium, provides buoyancy only for the weight of the balloons, not enough for the gondola. The other balloon is black, open, filled with martian gas. During the night, the gondola is on the ground. During the day, the black balloon, solar heated, takes the system to an altitude of 8 km and large distances can be covered during the flight. By venting the black balloon, the covered distance can be kept small, if wanted, and even, with the help of a guide rope, to “navigate” on the ground. The method can be used, not only for unique measurements on the ground, but also as a major ingredient for collecting on a global basis documented samples to be returned to Earth.

International audience; SODIUM clouds were released from Nike-Apache rockets launched from Fort Churchill, Manitoba (geomagnetic latitude 68.5° N.), on the evenings of May 21 and 22, 1963.

Both VEGA balloons encountered vertical winds with typical velocities of 1 to 2 meters per second. These values are consistent with those estimated from mixing length theory of thermal convection. However, small-scale temperature fluctuations for each balloon were sometimes larger than predicted. The approximate 6.5-kelvin difference in temperature consistently seen between VEGA-1 and VEGA-2 is probably due to synoptic or planetary-scale nonaxisymmetric disturbances that propagate westward with respect to the planet. There is also evidence from Doppler data for the existence of solar-fixed nonaxisymmetric motions that may be thermal tides. Surface topography may influence atmospheric motions experienced by the VEGA-2 balloon.

International audience; The VEGA Venus balloon radio transmissions received on Earth were used to measure the motion of the balloons and to obtain the data recorded by onboard sensors measuring atmospheric characteristics. Thus the balloons themselves, the gondolas, the onboard sensors, and the radio transmission system were all components of the experiment. A description of these elements is given, and a few details of data sampling and formatting are discussed.

The three-channel spectrometer (TKS) aboard the Vega 2 spacecraft recorded infrared and visible spectra near the nucleus of comet Halley. Spectra in the range 0.95–1.9 µm at a distance of 300 km from the nucleus reveal the H2O 1.38-µm band and OH bands, the latter excited by dissociation of a parent molecule. Their production rates are 4 × 1029 and 1.7 × 1030 molecules s−1, respectively. The dust particle density is 0.35 g cm−3, typical of fluffy particles of interplanetary dust. Emissions of 10 species are observed in the range 275–715 nm at ∼4,000 km from the nucleus, and 6 of them are analysed in terms of production rates: QOH = 2×1030, QCH = 1029, = 6×1027, = 3×1027, QCN = 1027 and QNH = 2 × 1026, all in molecules s−1. The difference between the OH and H2O production rates is puzzling and needs further analysis. Ionic emissions, not discussed here, are prominent in the tailward part of the comet.

Extreme ultraviolet spectral observations of the Jovian planetary system made during the Voyager 2 encounter have extended our knowledge of many of the phenomena and physical processes discovered by the Voyager 1 ultraviolet spectrometer. In the 4 months between encounters, the radiation from Io's plasma torus has increased in intensity by a factor of about 2. This change was accompanied by a decrease in plasma temperature of about 30 percent. The high-latitude auroral zones have been positively associated with the magnetic projection of the plasma torus onto the planet. Emission in molecular hydrogen bands has been detected from the equatorial regions of Jupiter, indicating planetwide electron precipitation. Hydrogen Lyman alpha from the dark side of the planet has been measured at an intensity of about 1 kilorayleigh. An observation of the occultation of alpha Leonis by Jupiter was carried out successfully and the data are being analyzed in detail.

International audience; The global hydrogen Lyman α, helium (584 angstroms), and molecular hydrogen band emissions from Saturn are qualitatively similar to those of Jupiter, but the Saturn observations emphasize that the H2 band excitation mechanism is closely related to the solar flux. Auroras occur near 80° latitude, suggesting Earth-like magnetotail activity, quite different from the dominant Io plasma torus mechanism at Jupiter. No ion emissions have been detected from the magnetosphere of Saturn, but the rings have a hydrogen atmosphere; atomic hydrogen is also present in a torus between 8 and 25 Saturn radii. Nitrogen emission excited by particles has been detected in the Titan dayglow and bright limb scans. Enhancement of the nitrogen emission is observed in the region of interaction between Titan's atmosphere and the corotating plasma in Saturn's plasmasphere. No particle-excited emission has been detected from the dark atmosphere of Titan. The absorption profile of the atmosphere determined by the solar occultation experiment, combined with constraints from the dayglow observations and temperature information, indicate that N2 is the dominant species. A double layer structure has been detected above Titan's limb. One of the layers may be related to visible layers in the images of Titan.

International audience; The Voyager Ultraviolet Spectrometer (UVS) is an objective grating spectrometer covering the wavelength range of 500–1700 Å with 10 Å resolution. Its primary goal is the determination of the composition and structure of the atmospheres of Jupiter, Saturn, Uranus and several of their satellites. The capability for two very different observational modes have been combined in a single instrument. Observations in the airglow mode measure radiation from the atmosphere due to resonant scattering of the solar flux or energetic particle bombardment, and the occultation mode provides measurements of the atmospheric extinction of solar or stellar radiation as the spacecraft enters the shadow zone behind the target. In addition to the primary goal of the solar system atmospheric measurements, the UVS is expected to make valuable contributions to stellar astronomy at wavelengths below 1000 Å.

Spectrophotometric observations of the inner coma of comet Halley in the range 275-710 nm were conducted from Vega 2 on March 8, 9, 10, 11, 1986. During the encounter session, when the impact parameter was minimum, p = 120 km, the gaseous emissions were still present, superimposed on an intense continuum. In the inner coma, C2 and C3 emissions steadily increase when the impact parameter decreases. The emissions of OH at 309 nm and CN in its band head at 388 nm show a plateau between 1500 and 600 km. The decrease in OH emission when the impact parameter is less than 500 km is interpreted in terms of high optical thickness of water vapor at Lyman-alpha. Pixel-to-pixel ratios of spectra show that the color of dust continuum presents small fluctuations which might be produced by a discontinuous emission of icy grains.

Preliminary results of the nephelometer experiments conducted aboard the large sounder, day, north, and night probes of the Pioneer Venus mission are presented. The vertical structures of the Venus clouds observed simultaneously at each of the four locations from altitudes of from 63 kilometers to the surface are compared, and similarities and differences are noted. Tentative results from attempting to use the data from the nephelometer and cloud particle size spectrometer on the sounder probe to identify the indices of refraction of cloud particles in various regions of the Venus clouds are reported. Finally the nephelometer readings for the day probe during impact on the surface of Venus are presented.

The lidar should not be considered for routine observations, which can be better made with passive remote sensing devices operated on board smaller spacecraft, but should be devoted to specific tasks.

Mass spectra of cometary dust particles measured by the PIA dust particle analyzer aboard the Giotto spacecraft show some unexpected and striking features. First, small particles below 10 to the -14th g are much more abundant than anticipated by models. Second, most of the particles are rich in light elements such as H, C, N, and O, suggesting the validity of models that describe the cometary dust as including organic material. Third, the light elements specifically seem to have a low ratio of mass to volume. Three examples of original mass spectra showing typical compositions are given; these have been measured, and are compared with a computer-simulated mass spectrum.

Two airglow experiments were carried by the OGO 4 and OGO 6 satellites launched on 27 July, 1967, and 5 June, 1969, respectively. The observations cover a period of maximum solar activity and show latitude and longitude effects in the low latitude nightglow 6300 A emission. The purpose of this paper is to present an interpretation of the main features of the nightglow 6300 A morphology in tropical regions in terms of the thermospheric dynamics.

International audience; Eight ultra-violet monochromatic pictures at the limb of the sun are analyzed for evidence of granulation in this spectral range (λ = 2000 Å). The spectral window (125 Å) is defined by two interference filters. These high-resolution pictures were obtained with a 20 cm Cassegrain telescope carried at 30 500 m of altitude by a stratospheric balloon. The resolution of the telescope is 1″. The instrument is mounted on a sunpointing control of excellent short time stability (2″). The pictures were taken at intervals of 210 seconds with a 0.25 second exposure. Large brilliant irregularities 10″ to 20″ in diameter are interpreted as chromospheric microfaculae with a half-hour lifetime. On the other hand, the smaller irregularities are interpreted as ultra-violet granulation. Using the correlation and structure functions, the analysis of the density distribution shows that spatial correlation of these irregularities is limited to a 4″ range.; Huit photographies monochromatiques (λ=2000 Å) au bord du soleil sont analysées en vue de mettre en évidence la granulation dans le domaine ultra-violet lointain. La fenêtre spectrale est définie par deux filtres interférentiels qui donnent une bande passante à mi-hauteur de 125 Å. Ces clichés de haute résolution ont été obtenus en ballon stratosphérique à une altitude de 30 500 m en profitant d'une fenêtre de transparence atmosphérique et en utilisant un télescope Cassegrain de 20 cm d'ouverture dont la résolution atteint 1″. Ce télescope était porté par un dispositif pointeur de soleil dont la stabilité à court terme était meilleure que 2″. Les clichés ont été pris à intervalles de 210 secondes avec un temps de pose de 0.25 seconde. On observe d'une part des variations de brillance grossières de largeur comprise entre 10″ et 20″ qui sont interprétées comme microfacules chromosphériques de durée de vie supérieure à 1/2 heure. On observe d'autre part une granulation dont la distribution densitométrique pour laquelle on a calculé les fonctions de corrélation et de structure présente une corrélation limitée à une distance angulaire de 4″.

International audience; Observation of the sodium dayglow in the scattered sunlight observed on the surface of the earth with a magnetic scanning photometer is reported. The intensity (September to November 1960) is unexpectedly strong—30 kilorayleighs toward the zenith—and evidence is that during the period studied the amount of sodium is 4 times as large in the daytime as at twilight. However, a strong correlation is found between the dayglow and twilight intensities. The abundance can be as high as 40×109 atoms/cm2. The possible role of water vapor absorption in the results is discussed.

International audience; The method that has been used in the past to determine the position of superpressure balloons employed in long- term meteorological and technological experiments-projects GHOST (Global Horizontal Sounding Technique), EOLE (French, God of the Winds), SOMEX (Solar Monitoring Experiment), ctc.-was to measure the solar elevation during the daylight hours and then compute the balloon position at local noon: latitude by the noon solar altitude and longitude by the time of balloon noon. This method has disadvantages: it requires a lengthy series of measure ments during the day and has degraded accuracy when the maximum solar angle approaches 90’. Another method was therefore devised in which the solar angle data are complemented by data that indicate the local geomagnetic rigidity; the correlation of the two data yields an improved position determination algorithm. This method was applied to the trajectory determination of the SOMEX balloons with considerable success.

Balmer alpha emissions of intensity larger than three times the nominal value have been recorded during five different nights at geomagnetic latitudes inferior to plus or minus 22 deg . They are correlated with sudden impulses in magnetograms. (auth)

International audience; OBSERVATIONS of the intensity of the zodiacal light at 6530 Å have been made with a photometer on board the satellite D2A ‘Tournesol’. This satellite was launched on April 15, 1971, from Kourou (French Guiana) into an orbit of inclination 46° with a perigee of 456 km and an apogee of 700 km. The spin axis was oriented towards the Sun with an accuracy of ∼15 arc min and a spin period of 60 s (Fig. 1). The line of sight of the photometer is perpendicular to the spin axis and therefore scans the celestial sphere in a plane orthogonal to the ecliptic plane and to the direction of the Sun. Observations in a plane perpendicular to the Earth-Sun line (that is, at elongation ε=90° or ε=−90°) were carried out during the night phase, when the solar depression angle was >25° and the altitude of the lowest observed points was >135 km. Because of this, the signal contained no contribution from the night-glow, but was only due to zodiacal light and starlight. The data cover, without interruption, the period from April 19, 1971, to June 1973.

Results from the occultation of the sun by Neptune imply a temperature of 750 + or - 150 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane, acetylene, and ethane at lower levels. The ultraviolet spectrum of the sunlit atmosphere of Neptune resembles the spectra of the Jupiter, Saturn, and Uranus atmospheres in that it is dominated by the emissions of H Lyman alpha (340 + or - 20 rayleighs) and molecular hydrogen. The extreme ultraviolet emission in the range from 800 to 1100 angstroms at the four planets visited by Voyager scale approximately as the inverse square of their heliocentric distances. Weak auroral emissions have been tentatively identified on the night side of Neptune. Airglow and occultation observations of Triton's atmosphere show that it is composed mainly of molecular nitrogen, with a trace of methane near the surface. The temperature of Triton's upper atmosphere is 95 + or - 5 kelvins, and the surface pressure is roughly 14 microbars.

International audience; WE present solar occultation measurements, taken from Phobos 2, of the H2O and CO2 bands at 1.9 μm and of the dust absorption at 1.9 and 3.7 μin. From these, we have calculated vertical profiles of water vapour, dust and atmosphere temperature in the range of 10–70 km. The water-vapour mixing-ratio profile demonstrates oscillations from 10-5 to 10-3 with a period of 25 km. We explain this behaviour by the condensation and evaporation of water at minima and maxima of the temperature oscillations.

We are deeply disturbed by the recent escalation of political assaults on scientists in general and on climate scientists in particular. All citizens should understand some basic scientific facts. There is always some uncertainty associated with scientific conclusions; science never absolutely proves anything. When someone says that society should wait until scientists are absolutely certain before taking any action, it is the same as saying society should never take action. For a problem as potentially catastrophic as climate change, taking no action poses a dangerous risk for our planet.

Stable subauroral red arcs (SAR arcs) were observed in both the northern and southern hemispheres on Sept. 28 to 30, 1967. For each pass the universal time and the longitude of the spacecraft as it crossed the magnetic equator are given. The SAR arc was noted to be worldwide in its extent and located on the same L shell in the northern and southern hemispheres. It appeared near L equals 3, moved equatorward to L equals 2.4, and later moved to, or reformed, near L equals 2.9. Its intensities were variable over the nearly two days of observations and, apparently influenced by the composition of the lower thermosphere, averaged 60 per cent greater in the northern hemisphere.

A global array of 20 radio observatories was used to measure the three-dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the Venus atmosphere by the VEGA spacecraft.

In June 1985, two instrumented balloons were placed in the atmosphere of Venus as part of the VEGA mission. Each balloon traveled about 30 percent of the way around the planet at a float altitude near 54 kilometers. In situ sensors measured pressure, temperature, vertical wind velocity, cloud particle backscatter, ambient light level, and frequency of lightning. A ground-based network of 20 radio antennas tracked the balloons by very long baseline interferometry (VLBI) techniques to monitor the Venus winds. The history, organization, and principal characteristics of this international balloon experiment are described.

International audience

The nephelometer measurements by the four Pioneer Venus probes reveal an upper haze area in the vertical cloud structure with several less clearly delineated layers in the main cloud bank. Concentrated sulfuric acid is the main component of the majority of the particulate matter in the clouds; the near UV radiation is absorbed by the clouds. The particles ejected from the planet surface are in the 10 to 100 micron range.