Betelgeuse, one of the most studied red supergiant stars1,2, dimmed in the optical range by ~1.2 mag between late 2019 and early 2020, reaching a historical minimum3–5 called ‘the Great Dimming’. Thanks to enormous observational effort to date, two hypotheses remain that can explain the Dimming1: a decrease in the effective temperature6,7 and an enhancement of the extinction caused by newly produced circumstellar dust8,9. However, the lack of multiwavelength monitoring observations, especially in the mid-infrared, where emission from circumstellar dust can be detected, has prevented us from closely examining these hypotheses. Here we present 4.5 yr, 16-band photometry of Betelgeuse between 2017 and 2021 in the 0.45–13.5 μm wavelength range making use of images taken by the Himawari-810 geostationary meteorological satellite. By examining the optical and near-infrared light curves, we show that both a decreased effective temperature and increased dust extinction may have contributed by almost equal amounts to the Great Dimming. Moreover, using the mid-infrared light curves, we find that the enhanced circumstellar extinction actually contributed to the Dimming. Thus, the Dimming event of Betelgeuse provides us with an opportunity to examine the mechanism responsible for the mass loss of red supergiants, which affects the fate of massive stars as supernovae11.

The structures and formation mechanisms of cirrus banding are investigated by analyzing radiosonde observations, conducting high-resolution numerical experiments, and performing linear stability analyses. In all 29 cases of cirrus bands that were analyzed, radiosonde observational data indicate that statically unstable layers exist. The detected banding clouds were aligned nearly parallel to the vertical shear vector in the unstable layer. In high-resolution numerical experiments using the cloud-resolving model SCALE-RM, cirrus bands forming in the outflow layer of a tropical cyclone are explicitly simulated. The existence of statically unstable layers and band-parallel background vertical wind shear are commonly identified in the simulations. Sensitivity experiments and heat budget analyses demonstrated that the unstable stratification within the cirrus clouds was maintained by the cloud-radiation interactions. To reveal the behavior of fluid instabilities in the cirrus bands, linear stability analyses in a basic state constructed from the radiosonde observations were performed. The fastest-growing disturbance is highly similar to that of the previously known thermal-shear instability in a uniform and isolated unstable layer and the results obtained by radiosonde observations and numerical simulations. All of the results consistently indicate that thermal-shear instability is responsible for the formation of cirrus banding. Our results not only follow previous modeling studies but also provide observational support, quantification of the destabilization by the cloud-radiation interactions, as well as a theoretical basis of the thermal-shear instability in a complex environment near cirrus bands.

A novel lightweight and high-accuracy variant of the image pan-sharpening tech-2 nique is designed for Himawari-8 multispectral images. This method, named 3 Additive Template Sharpening, injects higher-wavenumber components of the 4 highest-resolution Band 3 images into lower-resolution visible or shortwave in-5 frared images, thereby providing multispectral high-resolution images. This in-6 jection is realized by adding inter-band differential field to the high-resolution 7 band, making use of the specific pixel arrangement of the Himawari-8 imager for 8 2 K. Yamazaki, Image sharpening method suitable for Himawari-8 images simple and accurate coordinate transformations. Both subjective inspection of RGB composite images and objective evaluation of the upsampling indicate thatAdditive Template Sharpening exhibits higher accuracy than existing methods for Bands 1-6 of Himawari-8. This technique not only enables operational forecasters to diagnose atmospheric conditions in more details using higher-resolution RGB composites, but also provides higher-quality true-color imagery for the public.