Sodium in the Upper Atmosphere.

Cabannes, Jean; Dufay, Jean; Gauzit, J.

doi:10.1086/143967

Cited by 25 publications

(6 citation statements)

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“…Fluorescence from a meteoritic metallic vapor layer, like that detected by Schneider et al (2015) on Mars following the C/ 2013 A1 encounter, may also be observable near the terminator -particularly near the northern limb, where the apparent column density is elevated by foreshortening. One appealing candidate is Na I, whose D lines are readily observable from the ground and for which a persistent meteoritic layer of 10 13 -10 14 atoms m −2 is well observed over Earth (e.g., Cabannes et al 1938;Chapman 1939;Chamberlain 1956). As on Earth, Venus's low heliocentric radial velocity of −0.2 km s −1 during the encounter, combined with the deep Na I D Fraunhofer absorption lines in the solar spectrum, strongly suppresses the intensity of the resonance emission, with a fluorescence efficiency of ∼1 photon s −1 atom −1 for the D2 (589.0 nm) line.…”

Section: Meteor Observabilitymentioning

confidence: 99%

Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus

Zhang

Vissapragada

et al. 2021

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Long-period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au on 2021 December 18 and may subsequently graze the planet with its dust trail less than 2 days later. We observed C/2021 A1 with the Lowell Discovery Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale Telescope on 2021 March 20, while the comet was inbound at heliocentric distances of r = 4.97, 4.46, and 4.28 au, respectively. Tail morphology suggests that the dust is optically dominated by ∼0.1-1 mm radius grains produced in the prior year. Neither narrowband imaging photometry nor spectrophotometry reveal any definitive gas emission, placing 3σ upper bounds on CN production of 10 23 molec −1 at both of the latter two epochs. Trajectory analysis indicates that large (1 mm) grains ejected at extremely large heliocentric distances (r  30 au) are most strongly favored to reach Venus. The flux of such meteors on Venus, and thus their potential direct or indirect observability, is highly uncertain, as the comet's dust production history is poorly constrained at these distances but will likely fall well below the meteor flux from comet C/2013 A1 (Siding Spring)ʼs closer encounter to Mars in 2014 and thus poses a negligible risk to any spacecraft in orbit around Venus. Dust produced in previous apparitions will not likely contribute substantially to the meteor flux, nor will dust from any future activity apart from an unlikely high-speed (0.5 km s −1 ) dust outburst prior to the comet reaching r ≈ 2 au in 2021 September.Unified Astronomy Thesaurus concepts: Comet tails (274); Long period comets (933); Meteor trails (1036); Venus (1763)

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Section: Meteor Observabilitymentioning

confidence: 99%

Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus

Zhang

Vissapragada

et al. 2021

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“…During the 35 years or so following Babcock's measurement, other observations were attempted [6][7][8][9][10] using instruments with photographic plates as detectors, but only limited quantitative information on the upper atmosphere was derived [11][12][13][14][15][16][17][18][19]. Although the most obvious drawback to these measurements was the low quantum efficiency and non-linear behaviour of photographic emulsions, the Fabry-Perot silver mirror coatings employed were also significantly inferior to the multilayer dielectric coatings used today.…”

Section: Historical Development Of Optical Remote Sensingmentioning

confidence: 99%

Optical measurements of winds and kinetic temperatures in the upper atmosphere

Hernández

Killeen

1988

Advances in Space Research

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was used to determine the thermospheric neutral motions in the auroral zone. These measurements were compared with simultaneously measured ion drifts, obtained with the Chatanika incoherent backscatter radar [73], see Figure 3. This comparison showed that the neutral wind in the evening sector flowed in a generally sunward direction, in correspondence with the direction of ion convection, but opposite to that which would be expected from a consideration of solar heating alone. Further analysis of the 1972-73 data set [74] was presented, together with a modelling study of the auroral momentum equation, to suggest that ion drag was playing an important role in establishing the sunward neutral wind. This work was in accord with independent experimental results using rocket chemical release vapour trail analysis [75-77]. A more recent paper [78] has compared the optical meridional wind measurements made in Alaska during 1972 with determinations of the same parameter made using the Chatanika incoherent scatter radar. Reasonable agreement was found between the two (optical and radar) techniques, both for averaged wind patterns and for simultaneously observed winds from individual nights; this is illustrated in Figure 4. The experimental results from this study were also compared with the predictions of the NCAR-TGCM; the comparison indicated reasonable agreement and was suggestive of a possible heat source poleward of Chatanika.

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“…(0) NaO + 0 = Na + 02 • CHAPMAN (11) suggested that there was no necessary contra diction between BERNA.RD'S (9) height estimate or 60laa and the estimate by CABANNES, DUFAY & GAUZIT (10) ot l30km.…”

Section: Generalmentioning

confidence: 99%

“…BERNARD'S (9) estimate was based on observations or the enhanced twilight emission and therefore the emission at the lower levels where the sodium density was great est, whereas the night sky emission on which the measure ments of CABANNES, DUFlY & GAUZIT (10) were based doubt less occurred at a much higher level. On the basis of the ehemical reactions described above, having regard to the vertical distribution or 0 and ° CHAPMAN (11) 3 , suggested an exponential distribution for the free sodium with an abrupt decrease in density at the lower edge.…”

Section: Generalmentioning

confidence: 99%

Absorption of Sunlight by Atmospheric Sodium

Scrimger¹,

Hunten²

1957

Can. J. Phys.

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A photometer has been built which is sensitive to light only in a very narrow spectral region near the sodium D-lines. The light is scattered by sodium vapor at low density and the scattered light recorded by a photoelectric spectrometer. The latter resolves the two lines and allows the effect of stray light to be eliminated. With sunlight as the source, the radiation detected is at the bottom of the Fraunhofer lines and the residual intensity there may be measured. It is found that this intensity decreases slightly (relative to the continuum) as the sun approaches the horizon. This effect is attributed to atmospheric sodium; the amount found by this method agrees well with that deduced from twilight measurements. The thickness of the sodium layer in atoms/cm.2 varies between 3 and 9 × 109 in winter and is about 1 × 109 in April. The measurements also give the residual intensities of the Fraunhofer lines in the incident sunlight, averaged over the whole of the sun's disk. These are (5.90 ± 0.46)% for D1 and (5.06 ± 0.24)% for D2.

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Sodium in the Upper Atmosphere.

Cited by 25 publications

References 0 publications

Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus

Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus

Optical measurements of winds and kinetic temperatures in the upper atmosphere

Absorption of Sunlight by Atmospheric Sodium

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