The first assimilation of Akatsuki single-layer winds and its validation with Venusian atmospheric waves excited by solar heating.

The planetary missions including the Venus Climate Orbiter 'Akatsuki' provide new information on various atmospheric phenomena. Nevertheless, it is difficult to elucidate their three-dimensional structures globally and continuously only from observations because satellite observations are considerably limited in time and space. We constructed the first 'objective analysis' of Venus' atmosphere by assimilating cloud-top horizontal winds on the dayside from the equator to mid-latitudes, which is frequently obtained from Akatsuki's Ultraviolet Imager (UVI).

The nightside cloud-top circulation of the atmosphere of Venus.

Although Venus is a terrestrial planet similar to Earth, its atmospheric circulation is much different and poorly characterized. Winds at the cloud top have been measured predominantly on the dayside. Prominent poleward drifts have been observed with dayside cloud tracking and interpreted to be caused by thermal tides and a Hadley circulation; however, the lack of nightside measurements over broad latitudes has prevented the unambiguous characterization of these components.

How waves and turbulence maintain the super-rotation of Venus' atmosphere.

Venus has a thick atmosphere that rotates 60 times as fast as the surface, a phenomenon known as super-rotation. We use data obtained from the orbiting Akatsuki spacecraft to investigate how the super-rotation is maintained in the cloud layer, where the rotation speed is highest. A thermally induced latitudinal-vertical circulation acts to homogenize the distribution of the angular momentum around the rotational axis.

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

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.

Ultraviolet imager on Venus orbiter and its initial results.

The ultraviolet imager (UVI) has been developed for the spacecraft (Venus Climate Orbiter mission). The UVI takes ultraviolet (UV) images of the solar radiation reflected by the Venusian clouds with narrow bandpass filters centered at the 283 and 365 nm wavelengths. There are absorption bands of SO and unknown absorbers in these wavelength regions.

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

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.

Pacific Ocean decadal forcing of long-term changes in the western Pacific subtropical high.

The western Pacific subtropical high (WPSH) has a significant effect on droughts, heat waves, and tropical cyclone tracks over East Asia and the northwest Pacific. The WPSH has intensified during the past three decades, but its causes are not yet well understood. Here we show that the Pacific Decadal Oscillation (PDO) is responsible for the long-term changes in the WPSH through the meridional shift of the subtropical jet, based on comprehensive data analysis and model results.