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Hydroclimatic process in the Yarlung Tsangpo River (YTR) basin, a sensitive area to climate change, is obviously changing during recent years, but there has limited understanding about it. In this study, we investigated the spatiotemporal variation of precipitation over last four decades in the basin and the impact thereon of the changing Indian summer monsoon at interannual and decadal time scales. All the precipitation series have similar scaling behavior, reflecting similar climatic regime throughout the basin. However, the effect of the Indian monsoon strengthens from the downstream to upstream, causing spatial variability in the seasonal distribution of precipitation, and on this basis, the YTR basin is roughly divided into three regions: east, middle, and west. Both the occurrence times and magnitude of precipitation extremes, ranging 25-50mm/d, are exhibiting downward trends over the last four decades, which bodes well for water disaster controls in the basin. The Indian summer monsoon index, as an intensity indicator for the Indian summer monsoon, shows a positive relationship with the summer precipitation in the YTR basin. Periodic variability of the Indian monsoon determines the interannual nonstationary fluctuations of precipitation. Especially, the weakening effect of the Indian summer monsoon has caused an obvious decrease in precipitation over the rainy season after 1998. If the Indian summer monsoon keeps weakening, the precipitation would decrease and potentially water shortage would become more severe in the basin. Effective adaptation strategy should therefore be developed proactively to handle the unfavorable water situation, which is likely to occur in the future.

Spring snow cover variations over Eurasia consist of a same-sign component and a west-east dipole component. The same-sign component is dominant during late 1970s through 1980s, and the two components are equally important during 1990s and 2000s. Present study contrasted Eurasian spring and summer climate anomalies associated with western and eastern Eurasian spring snow cover variations and between 1975–1989 and 1993–2007 and found notable differences and obvious interdecadal changes in Eurasian climate anomalies. After 1990, spring surface temperature anomalies display an obvious west-east contrast pattern, consistent with a prominent atmospheric wave pattern over Eurasia. The temperature anomalies are larger corresponding to western than eastern Eurasian snow cover change. Snow-albedo effect plays a main role in temperature change during 1975–1989, whereas atmospheric processes also contribute largely to temperature change during 1993–2007. Large soil moisture anomalies occur corresponding to western Eurasian snow cover and during 1975–1989. The snow-hydrological effect on summer precipitation is mainly detected over the West Siberian Plain where soil moisture anomalies persist over 3 months. Over most of other Eurasian regions, atmospheric circulation pattern plays a dominant role in summer surface temperature and precipitation variations. The relationship of Indian summer rainfall to western Eurasian spring snow cover was weakened since the mid-1990s, and the correlation of Northeast China summer rainfall with local spring snow cover changed from positive to negative around 1990.

Using observational and reanalyses data, we investigated the impact of dust aerosols over the Middle East and the Arabian Sea (AS) on the Indian summer monsoon (ISM) rainfall. Satellite and aerosol reanalysis data show extremely heavy aerosol loading, mainly mineral dust, over the Middle East and AS during the ISM season. Multivariate empirical orthogonal function analyses suggest an aerosol-monsoon connection. This connection may be attributed to dust-induced atmospheric heating centered over the Iranian Plateau (IP), which enhances the meridional thermal contrast and strengthens the ISM circulation and rainfall. The enhanced circulation further transports more dust to the AS and IP, heating the atmosphere (positive feedback). The aerosols over the AS and the Arabian Peninsula have a significant correlation with rainfall over central and eastern India about 2 weeks later. This finding highlights the nonlocal radiative effect of dust on the ISM circulation and rainfall and may improve ISM rainfall forecasts.

[1] The relationship between interannual variations of the seasonal mean monsoon and intraseasonal oscillation (ISO) during boreal summer over the Indian monsoon region is investigated. The result shows a negative correlation between all-India summer monsoon rainfall and the ISO intensity. It is argued that the negative correlation is primarily attributed to the impact of the mean state of Indian summer monsoon on ISO. A strong Indian monsoon leads to the weakening of convection over the equatorial eastern Indian Ocean. The latter may further suppress the eastward and northward propagating ISO variances over the Indian Ocean and lead to a weakened intraseasonal activity over the Indian monsoon region. The ISO may feed back to the Indian summer mean monsoon through nonlinear eddy momentum transport. In addition, the ISO intensity over India increases (decreases) during the ENSO developing (decaying) summers.

Temperatures in Earth's lower stratosphere (from 14 to 22 km in altitude) were lower in September 1996 than at any other time since such temperatures were first systematically measured in 1979. Using microwave sensors aboard the TIROS-N series of polar-orbiting weather satellites, researchers from the Global Hydrology and Climate Center (GHCC) in Huntsville, Alabama, found that air in the stratosphere was 0.7°C cooler than the baseline temperature of the past 17 years. The cool month fits into what the researchers see as a 15-year cooling trend and is thought to be consistent with the depletion of ozone in the lower stratosphere.

The author's studies of the weather maps which characterize Indian Summer weather have led him to recognize a type of pressure distribution which uniformly gives several days of weather commonly called Indian Summer. This pressure distribution was described as a more or less stagnant area of high pressure over the southeastern States and a weak cyclonic area passing slowly down the Saint Lawrence Valley. The resulting winds are light, and the moderate chill of the early morning and evening resulting from a fairly well marked diurnal range of temperature is swept away by the genial warmth of the light southerly winds, and by the strong isolation of the daytime.