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Atmospheric gravity waves (AGWs) and medium‐scale traveling ionospheric disturbances (MSTIDs) in the upper atmosphere affect atmospheric circulation and radio‐wave transmission including satellite positioning and communications, and high‐frequency radio. The 3‐dimensional (3‐D) spectral analysis of airglow images makes it possible to extract wave parameters of AGWs and MSTIDs. Such spectral analysis of long‐term airglow images has not been performed in the southern part of Japan, which is a unique transition latitude from middle to equatorial region. In this study, we calculated the horizontal phase velocity distribution of AGWs in the mesosphere‐lower‐thermosphere (MLT), and MSTIDs in the F‐region ionosphere by applying the 3‐D spectral analysis method to the 557.7 and 630.0‐nm airglow images obtained at Sata (31.0°N, 130.7°E) in Japan over 20 years from 2000 to 2020. The spectra of AGWs in the MLT region in the 557.7‐nm airglow images show that the poleward (northward) power spectral density (PSD) is stronger in summer, suggesting that the tropospheric convection is a possible source of AGWs and the wave ducting propagation occurred. Westward propagation is also observed in winter, suggesting that wind filtering effect by mesospheric jets plays an important role. The PSD of MSTIDs in the 630‐nm airglow images increases during low solar activity periods, suggesting that MSTIDs are produced by ionospheric plasma instability. The westward PSD of MSTIDs is stronger in summer. These results are an important achievement in clarifying the statistical characteristics of AGWs and MSTIDs over Sata, Japan, based on long‐term airglow observations and 3‐D spectral analysis. Plain Language Summary: Atmospheric gravity waves (AGWs) and medium‐scale traveling ionospheric disturbances (MSTIDs) are important variabilities in the upper atmosphere because they affect the atmospheric circulation and the radio‐wave transmission including satellite positioning, respectively. AGWs and MSTIDs can be observed through airglow imaging, because airglow emission comes from mesopause region at altitudes of 80–100 km (AGW) and from the lower ionosphere at altitudes of 200–300 km (MSTID). The 3‐dimensional (3‐D) spectral analysis of airglow images makes it possible to extract parameters of AGWs and MSTIDs. Such spectral analysis over long‐term airglow images has not been done in the southern part of Japan which is a unique transition latitude from middle to equatorial region. In this study, we calculated the horizontal phase velocity distribution of AGWs in the mesopause region, and MSTIDs in the lower ionosphere by applying the 3‐D spectral analysis method to the 557.7 and 630.0‐nm airglow images, respectively, obtained at Sata (31.0°N, 130.7°E) in Japan over 20 years from 2000 to 2020. We report statistical characteristics of AGWs and MSTIDs over Sata, that is, seasonal, local time, and yearly variation of wave power and propagation direction, based on these long‐term airglow observations and 3‐D spectral analysis. Key Points: We obtained the horizontal phase velocity distribution of waves in 557.7 and 630.0‐nm airglow images at Sata, Japan, over 20 yearsTropospheric convection and mesospheric jet play an important role in atmospheric gravity waves in the mesopause regionPower spectrum density of medium‐scale traveling ionospheric disturbances in 630.0‐nm images increases during low solar activity period [ABSTRACT FROM AUTHOR]

Summer precipitation (June–August) increased markedly during the 2000s in Siberia, particularly in eastern Siberia. However, the nature of the mechanism that controlled this increase in precipitation remains under discussion. This study investigated the impacts of global warming on the trend of summer precipitation over northeastern Eurasia using large‐ensemble data from historical warming and nonwarming simulations for 1990–2010. Positive summer precipitation trends across Siberia reproduced in the ensemble mean of the historical simulation were similar to the observed data; however, negative trends observed over northeast China and Mongolia were not found in the ensemble mean. To extract members with a pattern of precipitation trend similar to that of the observations, empirical orthogonal function analysis was applied to the summer precipitation trend over Siberia for each simulation. The first leading mode in each simulation showed increase (decrease) in precipitation over eastern Siberia (northeast China), consistent with the spatial features of the observations. In the extracted members, the spatial pattern of the cyclonic (anticyclonic) circulation trend over northern parts of eastern Siberia (northeast China), associated with decadal and multidecadal variation, was amplified by global warming and resulted in an increasing trend of westerly moisture flux into eastern Siberia from western Siberia. Additionally, surface heating in northeast China, enhanced by global warming, might concurrently have intensified the cyclonic circulation over eastern Siberia. Furthermore, the results suggested that the reduced extent of Arctic sea ice coverage played a role in strengthening the cyclonic circulation over eastern Siberia and enhancing water vapour transport from the Arctic Ocean, which contributed to the strength of the westerly moisture flux over eastern Siberia. Although notable impacts of global warming on the precipitation trend in northeastern Eurasia were found, internal variation in the model experiments was also likely to have affected the precipitation trend, particularly in mid‐latitude regions. [ABSTRACT FROM AUTHOR]

The structure of mesoscale precipitation within monsoon depressions is still not as well‐known as the synoptic‐scale composite cloud and precipitation structure. Here, using observational data from multi‐satellite sensors and a cloud‐resolving regional model, we investigate the three‐dimensional structure of mesoscale precipitation systems in the different stages of the life cycle of a monsoon depression. Effects of latent heating from the precipitation systems and the Bay of Bengal (BoB) on the development of the monsoon depression are also evaluated in sensitivity experiments with the model. A typical monsoon depression developed on 17 August 2016 over the BoB. In the rapid development phase, satellite observations reveal mesoscale convective systems with deep convective precipitation cells and stratiform precipitation near the head of the BoB. Extremely deep and intense convective cells appear along a ring‐like rain band when a closed cyclonic circulation becomes obvious around the northernmost part of the BoB. The deep convection appears frequently, particularly along the western‐to‐southwestern side of the low, a convergence‐prone area between northerlies with air masses of large convective available potential energy (CAPE) that makes up the western–southwestern part of the closed cyclonic circulation, and strong monsoon westerlies with relatively stable air masses to the south of the low. Sensitivity experiments reveal that both cloud/precipitation processes and evaporation from the BoB are essential for the rapid development of the monsoon depression over the BoB. Evaporation from the BoB adds a large amount of moisture to the atmospheric boundary layer near the low. Southwesterlies and southerlies on the eastern side of the low draw in warm, humid boundary‐layer air to the closed cyclonic circulation, which maintains a large‐CAPE environment in the low and enhances deep convection. A possible positive feedback process including moist convection that leads to the rapid intensification of monsoon depressions over the BoB is discussed. [ABSTRACT FROM AUTHOR]

We analysed the long-term trend and interannual variability in summer (JJA) precipitation over eastern Siberia (90°-140°E, 50°-70°N) for the period 1979-2007. An increasing trend in summer precipitation was observed over large areas (Yenisei and Lena river basins) of eastern Siberia. Summer mean 850-hPa geopotential height decreased from Siberia to the marginal seas north of Siberia, with the largest decreases occurring over the northern part of eastern Siberia, while increasing trends were found around Mongolia, inducing a significant increase in westerly moisture flux and its convergence over eastern Siberia. Empirical orthogonal function (EOF) analysis of detrended summer precipitation revealed the leading modes of the interannual variability. The first leading mode (EOF1) represents interannual variation around the central Siberian Plateau and the middle reaches of the Lena river basin, related to the enhancement of a low-level cyclonic circulation centred on 65°N, 100°E around eastern Siberia. The circulation pattern of EOF1 closely matches the trend pattern over Siberia, indicating that a deeper quasi-stationary trough appears with increasing frequency in recent decades. The second leading mode (EOF2) shows a dipole pattern between the middle reaches of the Lena river basin and the western part of the Central Siberian Plateau. Wet summers in the Lena river basin are related to a stationary trough centred at around 60°N, 130°E. These leading patterns are related to the change in position of the stationary trough and the ridge of the wave train structure along the Arctic polar jet across the northern Eurasian continent. [ABSTRACT FROM AUTHOR]