HAL UVSQ
Not a member yet
57319 research outputs found
Sort by
Position determination methods used to track superpressure balloons
No full textInternational audienceThe 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
Limb-Darkening Observations between 1800 and 2900 Å
No full textInternational audienceWe succeeded in several attempts at measuring the solar limb-darkening in the continuous spectrum between 1800 Å and 2900 Å. Good spectroheliograms were obtained during a rocket flight in November 1964 and during a balloon flight in October 1966 at 2190 Å, 2665 Å, 2885 Å, and 1980 Å, 2235 Å respectively. A rocket flown at the beginning of 1967 provided excellent spectra allowing the measurement of center-to-limb variation in the continuum and lines from 1800 Å to 2800 Å. The first series of pictures yielded absolute values of the central intensity leading to a minimum temperature close to 4700 °K. The continuous opacity of the photosphere layers has been deduced from the two first experiments. It seems that a non-metallic source of continuous absorption must be taken into account between 2500 Å and 3000 Å. Moreover, as the source functions for the shortest wavelengths show a very flat variation near the minimum temperature, it seems that the transition zone between the photosphere and the chromosphere must be very gradual. These results are discussed in the light of the latest results deduced from the new spectra obtained
Mise en évidence de La granulation Solaire à 2000 Å
No full textInternational audienceEight 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″
Sudden Heating of the Ionosphere in the Auroral Zone
No full textInternational audienceSODIUM 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
Sodium dayglow: Observation and interpretation of a large diurnal variation
No full textInternational audienceAnalysis of the dayglow of the sodium D lines since September 1960 and the twilight glow since 1954 at Haute Provence Observatory shows a large seasonal maximum of 30 kR for the dayglow in June. The ratio of daytime to twilight abundance then is about 7 to 1. The ratio becomes 2 to 1 in December. Evidence presented for the reality of this effect includes actual line profiles showing an emission peak above Rayleigh-scattered background, observation of the dayglow from a high-altitude airplane, and observation of the dayglow with a rocket-borne photometer. The seasonal maximum is accompanied by a seasonal decrease of 5 km in twilight layer altitude in midsummer. The effect is interpreted as being caused by a diurnal variation in atomic oxygen and ozone enhanced by turbulent diffusion of the sodium and its compounds. Other possible interpretations such as photochemical excitation are rejected. A seasonal variation is also found in the ratio of morning to evening sodium abundance in twilight. The maximum ratio is 1.4 at the equinoxes. At Tromsø, Norway, the dayglow intensity is about 15 kR and shows no seasonal variation
Upper atmospheric turbulence determined by means of rockets
No full textInternational audienceThe motion field of the upper atmosphere was studied with the aid of sodium trails brought to the 100-km level by means of a Véronique rocket. Below 102 km the trail shows globular distortions in the form of elements having an average diameter of 0.5 km; above that height the trail is completely smooth, though highly curved, showing no small irregularities. The turbulence state of the upper atmosphere was studied by investigating diffusion of the sodium atoms. Above 102 km the broadening of the trail can be completely accounted for by molecular diffusion; below that height the observed rate of increase of the globule diameters can be explained only by assuming a combination of molecular and turbulent diffusion. This information and the increasing chemical differentiation above 102 km strongly indicate that the 100-km level marks the difference between the turbulent and the nonturbulent parts of the upper atmosphere. The absence of turbulence in the upper atmosphere is bound to be due to the increasing relative importance of the friction forces there. The Reynolds number rapidly decreases with increasing atmospheric height. The absence or occurrence of turbulence cannot be due to shear effects: the Richardson number is too great in the region studied by us, which shows that shear turbulence is not to be expected in this part of the earth's atmosphere. Since the energy fed into the turbulence field is rather small, turbulence cannot be fully developed; in fact, it is predicted that the turbulent element can only have diameters smaller than about 2 km, which is not in disagreement with the observed element diameter of 0.5 km. The smallest visible wavelength of the motion field is of the order 50 to 100 meters, in agreement with ionospheric investigations (20 to 60 meters) and theoretical predictions (60 meters)
The dayglow of the sodium D lines
No full textInternational audienceObservation 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
