Dataset Information

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki.

ABSTRACT: The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet's rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet's night-side escapes to space at narrow spectral windows of near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below about 57 km in altitude. Estimates of wind speeds have ranged from 50 to 70 m/s at low- to mid-latitudes, either nearly constant across latitudes or with winds peaking at mid-latitudes. Here we report the detection of winds at low latitude exceeding 80 m/s using IR2 camera images from the Akatsuki orbiter taken during July and August 2016. The angular speed around the planetary rotation axis peaks near the equator, which we suggest is consistent with an equatorial jet, a feature that has not been observed previously in the Venusian atmosphere. The mechanism producing the jet remains unclear. Our observations reveal variability in the zonal flow in the lower and middle cloud region that may provide new challenges and clues to the dynamics of Venus's atmospheric superrotation.

SUBMITTER: Horinouchi T

PROVIDER: S-EPMC5990972 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki.

Horinouchi Takeshi T Murakami Shin-Ya SY Satoh Takehiko T Peralta Javier J Ogohara Kazunori K Kouyama Toru T Imamura Takeshi T Kashimura Hiroki H Limaye Sanjay S SS McGouldrick Kevin K Nakamura Masato M Sato Takao M TM Sugiyama Ko-Ichiro KI Takagi Masahiro M Watanabe Shigeto S Yamada Manabu M Yamazaki Atsushi A Young Eliot F EF

Nature geoscience 20170828

The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet's rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet's night-side escapes to space at narrow spectral windows of near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below a ...[more]

PMID: 29887914

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Project description: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.

Project description:BackgroundThe use of severity of illness scoring systems such as the Acute Physiology and Chronic Health Evaluation in lower-middle income settings comes with important limitations, primarily due to data burden, missingness of key variables and lack of resources. To overcome these challenges, in Asia, a simplified model, designated as e-TropICS was previously developed. We sought to externally validate this model using data from a multi-centre critical care registry in India.MethodsSeven ICUs from the Indian Registry of IntenSive care(IRIS) contributed data to this study. Patients > 18 years of age with an ICU length of stay > 6 hours were included. Data including age, gender, co-morbidity, diagnostic category, type of admission, vital signs, laboratory measurements and outcomes were collected for all admissions. e-TropICS was calculated as per original methods. The area under the receiver operator characteristic curve was used to express the model's power to discriminate between survivors and non-survivors. For all tests of significance, a 2-sided P less than or equal to 0.05 was considered to be significant. AUROC values were considered poor when ≤ to 0.70, adequate between 0.71 to 0.80, good between 0.81 to 0.90, and excellent at 0.91 or higher. Calibration was assessed using Hosmer-Lemeshow C -statistic.ResultsWe included data from 2062 consecutive patient episodes. The median age of the cohort was 60 and predominantly male (n = 1350, 65.47%). Mechanical Ventilation and vasopressors were administered at admission in 504 (24.44%) and 423 (20.51%) patients respectively. Overall, mortality at ICU discharge was 10.28% (n = 212). Discrimination (AUC) for the e-TropICS model was 0.83 (95% CI 0.812-0.839) with an HL C statistic p value of < 0.05. The best sensitivity and specificity (84% and 72% respectively) were achieved with the model at an optimal cut-off for probability of 0.29.Conclusione-TropICS has utility in the care of critically unwell patients in the South Asia region with good discriminative capacity. Further refinement of calibration in larger datasets from India and across the South-East Asia region will help in improving model performance.

Dataset Information

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki.

Publications

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki.

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