The Third Pole (TP) is experiencing rapid warming and is currently in its warmest period in the past 2,000 years. This paper reviews the latest development in multidisciplinary TP research associated with this warming. The rapid warming facilitates intense and broad glacier melt over most of the TP, although some glaciers in the northwest are advancing. By heating the atmosphere and reducing snow/ice albedo, aerosols also contribute to the glaciers melting. Glacier melt is accompanied by lake expansion and intensification of the water cycle over the TP. Precipitation has increased over the eastern and northwestern TP. Meanwhile, the TP is greening and most regions are experiencing advancing phenological trends, although over the southwest there is a spring phenological delay mainly in response to the recent decline in spring precipitation. Atmospheric and terrestrial thermal and dynamical processes over the TP affect the Asian monsoon at different scales. Recent evidence indicates substantial roles that mesoscale convective systems play in the TP’s precipitation as well as an association between soil moisture anomalies in the TP and the Indian monsoon. Moreover, an increase in geohazard events has been associated with recent environmental changes, some of which have had catastrophic consequences caused by glacial lake outbursts and landslides. Active debris flows are growing in both frequency of occurrences and spatial scale. Meanwhile, new types of disasters, such as the twin ice avalanches in Ali in 2016, are now appearing in the region. Adaptation and mitigation measures should be taken to help societies’ preparation for future environmental challenges. Some key issues for future TP studies are also discussed.

[1] This study revealed the formation processes of mesoscale convective systems (MCSs) over the eastern Tibetan Plateau (TP), associated with the establishment of subplateauscale convergences affected by the longitudinal surface wetness gradient. Composites of reanalysis data and satellite infrared images showed that large MCSs occurred in the afternoon under the condition of the eastward expansion of upper tropospheric anticyclone with the enhancement of near-surface low pressure in the western plateau. The low-level convergence was systematically formed through the eastward propagation of a thermally induced cyclonic circulation formed in the north central plateau before the day of the MCS genesis. A numerical model successively simulated the MCS occurrence processes with the diurnal evolution of convergences, namely, (1) the formation of horizontal wind shear between southwesterlies and northeasterlies over the strong heated land-surface causing a thermal low in the northwest, (2) the eastward propagation of the vorticity due to intensification of upper westerlies in the night, and (3) the MCS genesis by low-level convergences behind the migrated vortex with a convective instability condition over the eastern wet land surface. Numerical sensitivity experiments confirmed that eliminating either the western surface sensible heat flux or the eastern surface latent heat flux prevented the development of MCS. Namely, the enhanced southeast-northwest gradation of the plateau-scale soil moisture distribution could effectively form the MCSs in the eastern plateau during the monsoon season.Citation: Sugimoto, S., and K. Ueno (2010), Formation of mesoscale convective systems over the eastern Tibetan Plateau affected by plateau-scale heating contrasts,

A near‐future, 2‐K warming climate simulation comprising over 3,000 years of ensemble simulations was performed using 60‐km global and 20‐km regional atmospheric models. Even in the +2‐K climate, indices of extreme precipitation and dryness increased significantly in the extratropics compared with the historical climate. Mean precipitation increases in the rainy season and decreases in the dry season, indicating that the seasonal precipitation range becomes amplified with global warming. The intensification of precipitation and dryness from +2 to +4 K was also robust in the mean for climatological wet and arid regions. Around Japan, which was classified as a wet region, the regional atmospheric model predicts that the extreme hourly precipitation in the future climate becomes more extreme on hot days, but slightly weaker on cold days. This extreme precipitation has a high sensitivity to air temperature exceeding 7%/K.

Abstract. Subseasonal-to-seasonal (S2S) prediction, especially the prediction of extreme hydroclimate events such as droughts and floods, is not only scientifically challenging, but also has substantial societal impacts. Motivated by preliminary studies, the Global Energy and Water Exchanges (GEWEX)/Global Atmospheric System Study (GASS) has launched a new initiative called “Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction” (LS4P) as the first international grass-roots effort to introduce spring land surface temperature (LST)/subsurface temperature (SUBT) anomalies over high mountain areas as a crucial factor that can lead to significant improvement in precipitation prediction through the remote effects of land–atmosphere interactions. LS4P focuses on process understanding and predictability, and hence it is different from, and complements, other international projects that focus on the operational S2S prediction. More than 40 groups worldwide have participated in this effort, including 21 Earth system models, 9 regional climate models, and 7 data groups. This paper provides an overview of the history and objectives of LS4P, provides the first-phase experimental protocol (LS4P-I) which focuses on the remote effect of the Tibetan Plateau, discusses the LST/SUBT initialization, and presents the preliminary results. Multi-model ensemble experiments and analyses of observational data have revealed that the hydroclimatic effect of the spring LST on the Tibetan Plateau is not limited to the Yangtze River basin but may have a significant large-scale impact on summer precipitation beyond East Asia and its S2S prediction. Preliminary studies and analysis have also shown that LS4P models are unable to preserve the initialized LST anomalies in producing the observed anomalies largely for two main reasons: (i) inadequacies in the land models arising from total soil depths which are too shallow and the use of simplified parameterizations, which both tend to limit the soil memory; (ii) reanalysis data, which are used for initial conditions, have large discrepancies from the observed mean state and anomalies of LST over the Tibetan Plateau. Innovative approaches have been developed to largely overcome these problems.

The summer western Pacific subtropical high (WPSH) has intensified during the past three decades. However, the underlying mechanism is not yet well understood. Here, it is shown that baiu rainband activity in midsummer, which is part of the East Asian summer monsoon, plays an important role in recent intensification in the WPSH along the baiu rainband. In contrast with the WPSH, the summer Okhotsk high, which is located to the north of the baiu rainband, has weakened during the past three decades. The north–south contrasting changes between the two highs reflect a response to northward-moved and enhanced baiu heating, which intensifies the upper-tropospheric ridge, resulting in the baroclinic intensification of the WPSH. Regional climate model experiments also support the observational analysis. Therefore, baiu convective activity in midsummer can act as a major driver for the WPSH intensification. The results here suggest that the mechanism intensifying the summer North Pacific subtropical high clearly differs between the western and eastern Pacific.