The June‐July Yangtze flooding in 1998 and 2020 drew incredible attention owing to the extreme precipitation events and devastating societal/economic damages. However, the quantitative estimation of the moisture transport mechanism is intensely discussed but still unresolved. Here we investigated two events from a unique perspective of Eulerian atmospheric water tracers that tries to explain the two events from model physics. The results showed that the moisture supplies from the Northwest Pacific decreased despite of different inducements, whereas the southwest summer monsoon (SWSM)‐related moisture supplies exhibited conspicuous enhancements in both events, suggesting that the SWSM‐related moisture supplies controlled the occurrence of Yangtze flooding. The physical processes of the two events were further compared. The 2020 flooding was more severe than the 1998 event, which was related to the stronger advective convergences and in‐stratus condensations of the SWSM‐related moisture.

Accurate radiometric calibration is fundamental to quantitative remote sensing. In this article, a thermal infrared radiative transfer model is first established, and then, the on-orbit radiometric calibration of the thermal infrared channels 23 (8.55 $\mu \text{m}$ ), 24 (10.8 $\mu \text{m}$ ), and 25 (12.0 $\mu \text{m}$ ) of the advanced MEdium Resolution Spectral Imager (MERSI-2) on the Chinese Fengyun 3D (FY-3D) satellite is evaluated and corrected against the channels of the Advanced Himawari Imager (AHI) on Himawari 8 satellite using the double difference (DD) method. The results indicate that the on-orbit radiometric calibrations in FY-3D MERSI-2 channels 23, 24, and 25 are slightly biased and certain variations exist between January and July 2020. In January 2020, the on-orbit calibration of MERSI-2 channel 23 is statistically consistent with that of AHI channel 11, and the calibration bias (mean ±standard deviation at the mean) is 0.04 ±0.27 K, whereas they are $0.11~\pm ~0.49$ K and $- 0.30\,\,\pm \,\,0.50$ K in MERSI-2 channels 24 and 25, respectively. In July 2020, the on-orbit calibration of MERSI-2 channel 25 is very consistent with that of the AHI channels with a calibration bias of 0.06 ±0.31 K, while they are $- 0.18\,\,\pm \,\,0.23$ K and $- 0.27\,\,\pm \,\,0.30$ K in MERSI-2 channels 23 and 24, respectively. The radiometric calibration biases are finally corrected by the linear fits on the matching observations.

Based on Global/Regional Assimilation and PrEdiction System‐Global Forecast System and actual Spectral Response Functions (SRFs) of three Selected Single‐Passband Channels (Channels 5–7) of FengYun‐3D MicroWave Temperature Sounders‐2, impacts of actual SRFs on Brightness Temperature (TB) simulation were analyzed. Compared with simulation by ideal SRFs, averaged STandard DeViation and bias of Observation minus Background by actual SRFs decrease about −5.0% and 37.3%. The reductions on Equatorial regions are more obvious than middle and high latitudes. Five types of deformations were put forward to analyze their impacts on TB simulation. Attenuation, shifting, and extending of passband have more impacts on simulated TB compared with trap on passband. The differences between TBs simulated using ideal and actual SRFs do not depend on the magnitude of the difference between ideal and actual SRFs, but on the balances of different types of deformations of actual SRF.

A special and unusual purple (magenta) haze episode was observed in Nanjing, China, at 17:00 on 22 December 2015. Many local and national news outlets reported this event. Based on an analysis of the pollution features and meteorological factors, including boundary layer characteristics, we concluded that this haze event was similar in most respects to other local haze episodes. We discuss the reasons and the possibilities about this rare color haze at the end of the paper. One way to attain a combination of blue and red light is to have the green wavelengths selectively absorbed, and this seems unlikely for typical atmospheric constituents. Another way involves pollution gases or particles together with small liquid-water drops, which need further confirmation. A third possibility is that the combination of transmitted red light from the sun and scattered blue light from above could produce a purple/magenta color in the sky. In general, further studies are required to assess the physical, chemical, and optical features of this purple haze in order to explain and predict this phenomenon in the future.

Accurate and stable radiometric calibration is a fundamental for quantitative remote sensing. This paper addresses the evaluation and correction of radiometric calibration biases in the middle infrared channel (the channel 6 centered at 3.8 μm) and the thermal infrared channels (the channels 7 and 8 centered at 10.8 μm and 12.0 μm respectively) of the MEdium Resolution Spectral Imager for the Rainfall Mission (MERSI-RM) on Fengyun-3G (FY-3G) satellite against the channels of the Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua satellite using the double difference (DD) method. First, an infrared radiative transfer model is constructed to simulate the observations in both middle infrared and thermal infrared channels, in which surface reflected solar irradiances are fully taken into account. Then, the matching samples between the MERSI-RM and MODIS observations in January, April, July and October of 2024 are collected in terms of the matching criteria. Next, the radiances at top of atmosphere (TOA) are simulated using the infrared radiative transfer model. Finally, the radiometric calibration biases in the MERSI-RM channels 6, 7 and 8 are evaluated and corrected. The results show that the impact of the simulation errors, the spectral response differences and geolocation errors on the final intercalibration results can be ignored. The radiometric calibration of the MERSI-RM channel 6 is quite consistent with that of the MODIS channel 20, while the radiometric calibrations in the MERSI-RM channels 7 and 8 are about 0.5 K underestimated. Although more or less calibration biases exist in the MERSI-RM channels, their on-orbit calibrations are generally stable in the four months of 2024.