Evidence for anomalous cloud particles at the poles of Venus

Wilson, Colin; Guerlet, Sandrine; Irwin, P. G. J.; Tsang, C. C. C.; Taylor, F. W.; Carlson, R. W.; Drossart, P.; Piccioni, G.

doi:10.1029/2008je003108

Cited by 46 publications

(27 citation statements)

References 33 publications

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“…The color variations illustrate the variation of opacities at the wavelengths arising from trace species and aerosol abundances other two wavelengths, and the reverse in areas where the features appear somewhat bluish. These differences appear consistent with influences of CO contribution at 2.32 µm ), H 2 SO 4 absorption (1.74 vs. 2.2 µm (Barstow et al 2012) and cloud particle size (1.74 vs. 2.3 µm, Wilson et al (2008)) and have been identified from Venus Express data. It seems that the compositional differences do not appear to be due to local time differences.…”

Section: Ribbons or Narrow Width Wavessupporting

confidence: 69%

Venus looks different from day to night across wavelengths: morphology from Akatsuki multispectral images

Limaye

Watanabe

Yamazaki

et al. 2018

Earth Planets Space

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Since insertion into orbit on December 7, 2015, the Akatsuki orbiter has returned global images of Venus from its four imaging cameras at eleven discrete wavelengths from ultraviolet (283 and 365 nm) and near infrared (0.9-2.3 µm), to the thermal infrared (8-12 µm) from a near-equatorial orbit. The Venus Express and Pioneer Venus Orbiter missions have also monitored the planet for long periods but from polar or near-polar orbits. The wavelength coverage and views of the planet also differ for all three missions. In reflected light, the images reveal features seen near the cloud tops (~ 70 km altitude), whereas in the near-infrared images of the nightside, features seen are at mid-to lower cloud levels (~ 48-60 km altitude). The dayside cloud cover imaged at the ultraviolet wavelengths shows morphologies similar to what was observed from Mariner 10, Pioneer Venus, Galileo, Venus Express and MESSENGER. The daytime images at 0.9 and 2.02 µm also reveal some interesting features which bear similarity to the ultraviolet images. The nighttime images at 1.74, 2.26 and 2.32 µm and at 8-12 µm reveal features not seen before and show new details of the nightside including narrow wavy ribbons, curved string-like features, long-scale waves, long dark streaks, isolated bright spots, sharp boundaries and even mesoscale vortices. Some features previously seen such as circum-equatorial belts (CEBs) and occasional areal brightenings at ultraviolet (seen in Venus Express observations) of the cloud cover at ultraviolet wavelengths have not been observed thus far. Evidence for the hemispheric vortex organization of the global circulation can be seen at all wavelengths on the day-and nightsides. Akatsuki images reveal new and puzzling morphology of the complex nightside cloud cover. The cloud morphologies provide some clues to the processes occurring in the atmosphere and are thus, a key diagnostic tool when quantitative dynamical analysis is not feasible due to insufficient information.

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Section: Ribbons or Narrow Width Wavessupporting

confidence: 69%

Venus looks different from day to night across wavelengths: morphology from Akatsuki multispectral images

Limaye

Watanabe

Yamazaki

et al. 2018

Earth Planets Space

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“…Opacity inhomogeneities due to particles with radius >3 μm at or near the cloud base (48-50 km altitudes) are believed to be responsible for such silhouettes (Grinspoon et al 1993), being consistent with the fact that they move at speeds lower than those at the cloud top (Sánchez-Lavega et al 2008). Accumulated data in these NIR windows have proved their usefulness in inferring the conditions in the middle-to-lower atmosphere (Carlson et al 1993;Taylor and Crisp 1997;Grinspoon et al 1993;Satoh et al 2009;Tsang et al 2008;Wilson et al 2008).…”

Section: Introductionmentioning

confidence: 81%

“…(3). While this changes m by 1.5 %, the obtained values for many pixels are statistically analyzed in a scatter plot (Carlson et al 1993;Wilson et al 2008). As 1.5 % errors may only slightly blur individual branches in the scatter plot (Carlson et al 1993), they therefore have little effect on the identification of branches.…”

Section: Effect Of Snr On the Cloud Size Parametersmentioning

confidence: 99%

“…Based on the analysis of Galileo/NIMS data, the following empirical formula has been proposed to describe the cloud size parameters (Carlson et al 1993): (m: size parameter, I 1.74µm : radiance at 1.74 µm, I 2.3µm : radiance at 2.3 μm). This simple yet useful formula has been used as a convenient tool to classify the clouds of different particle sizes (Carlson et al 1993;Wilson et al 2008). Carlson et al identified five branches of m parameter in Galileo/NIMS data and interpreted them as variations in mixing ratio of two distinctive modes of particles (one is ∼3 µm and another is ∼7 µm in diameter).…”

Section: Aerosol Propertiesmentioning

confidence: 99%

“…that may not be understood with snapshot data. Statistical analysis is therefore essential (Carlson et al 1993;Wilson et al 2008). IR2 will provide spatially resolved 1.74-and 2.3-μm images 2) is plotted for various sub-cloud CO abundances against the opacity of underlying cloud.…”

Section: Aerosol Propertiesmentioning

confidence: 99%

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Development and in-flight calibration of IR2: 2-μm camera onboard Japan’s Venus orbiter, Akatsuki

et al. 2016

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IR2, a near-infrared camera in the 2-μm region onboard Akatsuki has been developed to primarily study the middleto-lower atmospheric dynamics of Venus as probed in the 1.74-and 2.3-μm "windows" of the CO 2 atmosphere on the night side. The spatial and temporal variability of CO below the clouds is also studied by differentiating 2.32-μm CO-band images from simultaneous 2.26-μm images. Images of the night-side disk in these wavelengths will enable us to determine the zonal and meridional winds near the cloud-base altitudes. IR2 also images at 2.02 μm, the center of a CO 2 absorption band. Such images can visualize the variation of the cloud-top altitudes as contrast features due to different absorption path lengths of the reflected sunlight. Tracking of the 2.02-μm features will also enable us to obtain wind information at the cloud-top level. Together with the other cameras and the radio science equipment on Akatsuki, IR2 will contribute to understanding of the production and maintenance mechanism of super-rotation in the Venusian atmosphere. During cruise, IR2 observed zodiacal light with a broad-band H filter (1.65 μm), imaged the Earth-moon remotely from a distance of ~30 million km, and determined Venus's phase curves at small phase angles. We have just started the early phase operation check of IR2 at Venus, as the orbit insertion in December 2015 was successful.

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Analysis of the radiative budget of the Venusian atmosphere based on infrared Net Exchange Rate formalism

Lebonnois

Eymet²,

Lee

et al. 2015

JGR Planets

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A detailed one-dimensional analysis of the energy balance in Venus atmosphere is proposed in this work, based on the Net Exchange Rate formalism that allows the identification in each altitude region of the dominant energy exchanges controlling the temperature. Well-known parameters that control the temperature profile are the solar flux deposition and the cloud particle distribution. Balance between solar heating and infrared energy exchanges is analyzed for each region: upper atmosphere (from cloud top to 100 km), upper cloud, middle cloud, cloud base, and deep atmosphere (cloud base to surface). The energy accumulated below the clouds is transferred to the cloud base through infrared windows, mostly at 3-4 μm and 5-7 μm. The continuum opacity in these spectral regions is not well known for the hot temperatures and large pressures of Venus's deep atmosphere but strongly affects the temperature profile from cloud base to surface. From cloud base, upward transport of energy goes through convection and short-range radiative exchanges up to the middle cloud where the atmosphere is thin enough in the 20-30 μm window to cool directly to space. Total opacity in this spectral window between the 15 μm CO 2 band and the CO 2 collision-induced absorption has a strong impact on the temperature in the cloud convective layer. Improving our knowledge of the gas opacities in these different windows through new laboratory measurements or ab initio computations, as well as improving the constraints on cloud opacities would help to separate gas and cloud contributions and secure a better understanding of Venus's atmosphere energy balance.

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Evidence for anomalous cloud particles at the poles of Venus

Cited by 46 publications

References 33 publications

Venus looks different from day to night across wavelengths: morphology from Akatsuki multispectral images

Venus looks different from day to night across wavelengths: morphology from Akatsuki multispectral images

Development and in-flight calibration of IR2: 2-μm camera onboard Japan’s Venus orbiter, Akatsuki

Analysis of the radiative budget of the Venusian atmosphere based on infrared Net Exchange Rate formalism

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