Observation of a blue sun over new Mexico, U.S.A., on 19 April 1991

Horváth, H.; Metzig, G.; Preining, O.; Pueschel, R. F.

doi:10.1016/1352-2310(94)90039-6

Cited by 11 publications

(8 citation statements)

References 6 publications

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“…Particles with an average size of about 1-1.5 gm will create a relative increase in red-to-blue absorption, causing sunlight passing through to appear bluish. If, however, the particles are slightly smaller than this, with an average size of about 0.5 I.tm, the Sun will appear red as more blue light is scattered away from the viewer [Horvath et al, 1994]. In either case, relatively narrow size distributions are required as a broad distribution of particles will contribute all across the extinction curve and effectively wash out any color discrimination.…”

Section: Model Descriptionmentioning

confidence: 99%

Cloud formation under Mars Pathfinder conditions

Colaprete¹,

Toon²,

Magalhães³

1999

J. Geophys. Res.

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Section: Model Descriptionmentioning

confidence: 99%

Cloud formation under Mars Pathfinder conditions

Colaprete¹,

Toon²,

Magalhães³

1999

J. Geophys. Res.

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“…Radius (r) 0.5 μm Assuming a particle refractive index m = 1.5, the above range of parameter P from 4.1 to 7.7 corresponds to a range of aerosol particle radius from r = 0.36 μm (a purple sun) to r = 0.48 μm (a blue sun) and r = 0.67 μm (a green sun). Nonideal aerosols produced by natural sources likewise produce the observation of a purple, blue or green sun if their size distribution is dominated by particles in this narrow range (Penndorf, 1953;Horvath et al, 1994), although somewhat broader particle distributions may do so too (Horvath et al, 1994;Wullenweber et al, 2021).…”

Section: Aerosol Optical Depth and Massmentioning

confidence: 99%

“…At Earth's surface, however, its observed colour varies due to scattering and absorption by atmospheric gases and aerosols (Bohren & Huffman, 2004). A sufficiently dense aerosol of solid particles or liquid droplets with a radius of about 0.5 μm, and a refractive index of about 1.5 may alter the observed colour of the sun to a pronounced blue, purple or green (La Mer & Kerker, 1953;Penndorf, 1953;Van de Hulst, 1981;Porch, 1989;Horvath et al, 1994;Ehlers et al, 2014;Wullenweber et al, 2021). Such an aerosol is occasionally produced by a volcanic eruption, for example, the 1880 eruption of Cotopaxi, in Ecuador (Whymper, 1884) or the 1883 eruption of Krakatau, in Indonesia (Symons et al, 1888), or a forest fire, for example, the 1950 Chinchaga fire, in Canada (Bull, 1951;Wilson, 1951).…”

Section: Introductionmentioning

confidence: 99%

The blue suns of 1831: was the eruption of Ferdinandea, near Sicily, one of the largest volcanic climate forcing events of the nineteenth century?

Garrison

Kilburn

Smart

et al. 2021

Preprint

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Abstract. One of the largest climate forcing eruptions of the nineteenth century was, until recently, believed to have taken place at Babuyan Claro volcano, in the Philippines, in 1831. However, a recent investigation found no reliable evidence of such an eruption, suggesting that the 1831 eruption must have taken place elsewhere. A newly compiled dataset of reported observations of a blue, purple and green sun in August 1831 is here used to reconstruct the transport of a stratospheric aerosol plume from that eruption. The source of the aerosol plume is identified as the eruption of Ferdinandea, which took place about 50 km off the south-west coast of Sicily (lat. 37.1° N., long. 12.7° E.), in July and August 1831. The modest magnitude of this eruption, assigned a Volcanic Explosivity Index (VEI) of 3, has commonly caused it to be discounted or overlooked when identifying the likely source of the stratospheric sulphate aerosol in 1831. It is proposed, however, that convective instability in the troposphere contributed to aerosol reaching the stratosphere and that the aerosol load was enhanced by addition of a sedimentary sulphur component to the volcanic plume. One of the largest climate forcing volcanic eruptions of the nineteenth century would thus effectively have been hiding in plain sight, arguably ‘lowering the bar’ for the types of eruptions capable of having a substantial climate forcing impact. Prior estimates of the mass of stratospheric sulphate aerosol responsible for the 1831 Greenland ice-core sulphate deposition peaks which have assumed a source eruption at a low-latitude site will therefore have been overstated. The example presented in this paper serves as a useful reminder that VEI values were not intended to be reliably correlated with eruption sulphur yields unless supplemented with compositional analyses. It also underlines that eye-witness accounts of historical geophysical events should not be neglected as a source of valuable scientific data.

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“…At Earth's surface, however, its observed colour varies due to scattering and absorption by atmospheric gases and aerosols (Bohren and Huffman, 2004). A sufficiently dense aerosol of solid particles or liquid droplets with a radius of about 0.5 µm, and a refractive index of about 1.5 may alter the observed colour of the sun to a pronounced blue, purple or green (La Mer and Kerker, 1953;Penndorf, 1953;Van de Hulst, 1981;Porch, 1989;Horvath et al, 1994;Ehlers et al, 2014;Wullenweber et al, 2021). Such an aerosol is occasionally produced by a volcanic eruption, such as the 1880 eruption of Cotopaxi in Ecuador (Whymper, 1884) or the 1883 eruption of Krakatau in Indonesia (Symons et al, 1888), or by a forest fire, such as the 1950 Chinchaga fire in Canada (Bull, 1951;Wilson, 1951).…”

Section: Introductionmentioning

confidence: 99%

The blue suns of 1831: was the eruption of Ferdinandea, near Sicily, one of the largest volcanic climate forcing events of the nineteenth century?

et al. 2021

View full text Add to dashboard Cite

Abstract. One of the largest climate forcing eruptions of the nineteenth century was, until recently, believed to have taken place at the Babuyan Claro volcano, in the Philippines, in 1831. However, a recent investigation found no reliable evidence of such an eruption, suggesting that the 1831 eruption must have taken place elsewhere. We here present our newly compiled dataset of reported observations of a blue, purple and green sun in August 1831, which we use to reconstruct the transport of a stratospheric aerosol plume from that eruption. The source of the aerosol plume is identified as the eruption of Ferdinandea, which took place about 50 km off the south-west coast of Sicily (37.1∘ N, 12.7∘ E), in July and August 1831. The modest magnitude of this eruption, assigned a volcanic explosivity index (VEI) of 3, has commonly caused it to be discounted or overlooked when identifying the likely source of the stratospheric sulfate aerosol in 1831. It is proposed, however, that convective instability in the troposphere contributed to aerosol reaching the stratosphere and that the aerosol load was enhanced by addition of a sedimentary sulfur component to the volcanic plume. Thus, one of the largest climate forcing volcanic eruptions of the nineteenth century would effectively have been hiding in plain sight, arguably “lowering the bar” for the types of eruptions capable of having a substantial climate forcing impact. Prior estimates of the mass of stratospheric sulfate aerosol responsible for the 1831 Greenland ice core sulfate deposition peaks which have assumed a source eruption at a low-latitude site will, therefore, have been overstated. The example presented in this paper serves as a useful reminder that VEI values were not intended to be reliably correlated with eruption sulfur yields unless supplemented with compositional analyses. It also underlines that eye-witness accounts of historical geophysical events should not be neglected as a source of valuable scientific data.

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Observation of a blue sun over new Mexico, U.S.A., on 19 April 1991

Cited by 11 publications

References 6 publications

Cloud formation under Mars Pathfinder conditions

Cloud formation under Mars Pathfinder conditions

The blue suns of 1831: was the eruption of Ferdinandea, near Sicily, one of the largest volcanic climate forcing events of the nineteenth century?

The blue suns of 1831: was the eruption of Ferdinandea, near Sicily, one of the largest volcanic climate forcing events of the nineteenth century?

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