Periodic variations of oxygen EUV dayglow in the upper atmosphere of Venus: Hisaki/EXCEED observations

Masunaga, Kei; Seki, K.; Terada, Naoki; Tsuchiya, F.; Kimura, Tomoki; Yoshioka, Kazuo; Murakami, Go; Yamazaki, Atsushi; Kagitani, Masato; Tao, Chihiro; Fedorov, A.; Futaana, Yoshifumi; Zhang, T. L.; Shiota, Daikou; Leblanc, François; Chaufray, Jean‐Yves; Yoshikawa, Ichiro

doi:10.1002/2015je004849

Cited by 17 publications

(17 citation statements)

References 37 publications

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“…The data were provided by EXCEED onboard the Earthorbiting satellite Hisaki, which has produced quasi-continuous extreme ultraviolet (EUV) spectral images of solar planetary exospheres since its launch in 2013 Masunaga et al 2015). The EXCEED/ Hisaki observes a preselected target that satisfies the criterion that its elongation angle from the Sun exceeds 90° for outer planets or 25° for Venus and Mercury.…”

Section: Instrumentationmentioning

confidence: 99%

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Yoshikawa

Suzuki

Hikida

et al. 2017

Earth Planets Space

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Jupiter's moon Io, which orbits deep inside the magnetosphere, is the most geologically active object in the solar system. Kurdalagon Patera, a volcano on Io, erupted in 2015 and became a substantial source of Jovian magnetospheric plasma. Based on Earth-orbiting spacecraft observations, Io plasma torus (IPT) exhibited the peak intensity (nearly double) of ionic sulfur emissions roughly 2 month later, followed by a decay phase. This environmental change provides a unique opportunity to determine how the more heavily loaded magnetosphere behaves. Indeed, the extreme ultraviolet spectroscope for exospheric dynamics onboard the Earth-orbiting spacecraft Hisaki witnessed the whole interval via aurora and IPT observations. A simple-minded idea would be that the centrifugal force acting on fast co-rotating magnetic flux tubes loaded with heavier contents intensifies their outward transport. At the same time, there must be increased inward convection to conserve the magnetic flux. The latter could be accompanied by (1) increased inward velocity of field lines, (2) increased frequency of inward transport events, (3) increased inward flux carried per event, or (4) combinations of them. The Hisaki observations showed that the densities of major ions in the IPT increased and roughly doubled compared with pre-eruption values. The hot electron fraction, which sustains the EUV radiation from the IPT, gradually increased on a timescale of days. Pairs of intensified aurora and IPT brightening due to the enhanced supply of hot electrons from the mid-magnetosphere to the IPT upon aurora explosions observed during both quiet and active times, enabled the study of the mid-magnetosphere/IPT relationship. Hisaki observations under active Io conditions showed that: (1) the hot electron fraction in the torus gradually increased; (2) brightening pairs were more intense; (3) the energy supplied by the largest event maintained enhanced torus emission for less than a day; (4) the time delay of a torus brightening from a corresponding aurora intensification was roughly 11 h, that is, the same as during quiet times, suggesting that the inward convection speed of high-energy electrons does not change significantly.

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Section: Instrumentationmentioning

confidence: 99%

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Yoshikawa

Suzuki

Hikida

et al. 2017

Earth Planets Space

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“…The Hisaki satellite was launched in September 2013 and entered into the orbit with the altitude of 950-1150 km [Yoshikawa et al, 2014]. The main purposes of Hisaki/EXCEED are to investigate plasma dynamics in Jupiter's magnetosphere [Yoshikawa et al, 2010;Tsuchiya et al, 2010;Yoshioka et al, 2012] and interactions between the upper atmospheres of terrestrial planets (i.e., Venus and Mars) and the solar wind [e.g., Masunaga et al, 2015]. Because Hisaki is the space telescope dedicated for the solar system science and because Jupiter's magnetosphere is one of the major targets, we can perform long-term and continuous monitoring of IPT.…”

Section: Observationmentioning

confidence: 99%

Response of Jupiter's inner magnetosphere to the solar wind derived from extreme ultraviolet monitoring of the Io plasma torus

Murakami

Yoshioka

Yamazaki

et al. 2016

Geophysical Research Letters

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Because Jupiter's magnetosphere is huge and is rotationally dominated, solar wind influence on its inner part has been thought to be negligible. Meanwhile, dawn‐dusk asymmetric features of this region have been reported. Presence of dawn‐to‐dusk electric field is one of the leading explanations of the asymmetry; however, the physical process of generating such an intense electric field still remains unclear. Here we present long and continuous monitoring of the extreme ultraviolet emissions from the Io plasma torus in Jupiter's inner magnetosphere made by the Hisaki satellite between December 2013 and March 2014. We found five occasions where the dusk/dawn brightness ratio was enhanced above 2.5 in response to rapid increase of the solar wind dynamic pressure. The enhancement is achieved as the dusk region brightens and the dawn region dims. The observation indicates that dawn‐to‐dusk electric field in the inner magnetosphere is enhanced under compressed conditions.

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“…Kouyama et al (2015) showed, using a linear model for the vertical propagation of planetary-scale waves in the cloud-level atmosphere (60-80 km), that Kelvin waves cannot reach >75 km while the vertical propagation of Rossby waves highly depends on the vertical profile of the mean zonal wind. Masunaga et al (2015Masunaga et al ( , 2017 analyzed variations of the oxygen atom (O) dayglow intensity of the Venusian thermosphere on both dawnside and duskside using spectroscopic data obtained by the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on board the Hisaki spacecraft (Yoshikawa et al, 2014). They detected a periodicity of~4 Earth days in the dayglow intensity exclusively on the dawnside and pointed out that planetary-scale waves might be responsible for the periodic variations, although the existence of planetary-scale waves at thermospheric heights was not confirmed.…”

Section: Introductionmentioning

confidence: 99%

Vertical Coupling Between the Cloud‐Level Atmosphere and the Thermosphere of Venus Inferred From the Simultaneous Observations by Hisaki and Akatsuki

et al. 2020

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The vertical coupling between the cloud‐level atmosphere and the thermosphere of Venus was investigated using 365 nm images obtained by the Ultraviolet Imager on board Akatsuki and oxygen atom 135.6 nm dayglow intensities obtained by the Extreme Ultraviolet Spectroscope for Exospheric Dynamics on board the space telescope Hisaki. Simultaneous observations revealed a common periodicity of ~3.6 Earth days in the cloud‐tracked velocity, the cloud brightness, and the airglow intensity. The oscillation at the cloud level is attributed to a planetary‐scale Kelvin wave. A one‐dimensional linear wave model showed that the Kelvin wave cannot propagate from the cloud level to the thermosphere because of radiative damping. The modeling also revealed that a small‐scale gravity waves having wavelengths of <1,000 km can reach the thermosphere on the dawnside and that they are strongly attenuated on the duskside because of the difference in the background winds with vertical shears. We further developed a one‐dimensional photochemical model to investigate the response of the airglow intensity to the change of the eddy diffusion coefficient, which is expected to increase with the wave amplitude. The model showed that a 3.6‐day oscillation of the diffusion coefficient with an amplitude of ~300 m2 s−1 explains the observed airglow intensity variation. A possible cause of the 3.6‐day period is the filtering of gravity wave fluxes by the Kelvin wave‐induced wind.

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Periodic variations of oxygen EUV dayglow in the upper atmosphere of Venus: Hisaki/EXCEED observations

Cited by 17 publications

References 37 publications

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Response of Jupiter's inner magnetosphere to the solar wind derived from extreme ultraviolet monitoring of the Io plasma torus

Vertical Coupling Between the Cloud‐Level Atmosphere and the Thermosphere of Venus Inferred From the Simultaneous Observations by Hisaki and Akatsuki

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