P-wave waveforms in the distance range between 12° and 30° were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas. The waveform data from 504 earthquakes with magnitudes larger than 5.0 between 1990 and 2005 that occurred within 30° from the center of the Plateau were modelled. We divided the study area into 6 regions and modeled upper-mantle-distance P waveforms with turning points beneath each region separately. The results show that the upper-mantle P-wave velocity structures beneath India, the Himalayas, and the Lhasa Terrane are similar and contain a high-velocity lid about 250 km thick. The upper-mantle velocities down to 200 km beneath the Qiangtang Terrane, the Tarim Basin, and especially the Songpan-Garzê Terrane are lower than those in the south. The 410-km discontinuity beneath these two terranes is elevated by about 20 km. High-velocity anomalies are found in the transition zone below 500 km under the Lhasa and Qiangtang Terranes. The results suggest that the Tibetan Plateau was generated by thrusting of the Indian mantle lithosphere under the southern part of Tibet. Portions of the thickened Eurasian mantle lithosphere were delaminated; they are now sitting in the transition zone beneath southern Tibet and atop of the 410-km discontinuity underneath northern Tibet.
The unique geographical location and high altitude of the Tibetan Plateau can greatly influence regional weather and climate. In particular, the Asian summer monsoon (ASM) anticyclone circulation system over the Tibetan Plateau is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. To improve understanding of these physical processes, a multi-location joint atmospheric experiment was performed over the Tibetan Plateau from late July to August in 2018, funded by the five-year (2018–2022) STEAM (stratosphere and troposphere exchange experiment during ASM) project, during which multiple platforms/instruments—including long-duration stratospheric balloons, dropsondes, unmanned aerial vehicles, special sounding systems, and ground-based and satellite-borne instruments—will be deployed. These complementary methods of data acquisition are expected to provide comprehensive atmospheric parameters (aerosol, ozone, water vapor, CO2, CH4, CO, temperature, pressure, turbulence, radiation, lightning and wind); the richness of this approach is expected to advance our comprehension of key mechanisms associated with thermal, dynamical, radiative, and chemical transports over the Tibetan Plateau during ASM activity.