ALBERT

Description: A dataset obtained from wind-profile radars located along the north coast of China in summer was used to compare the characteristics of the low-level jets (LLJs) at two different sites, Tianjin and Shanghai. In this paper, the characteristics and evolutions of the low-level jets were investigated, and the inertial oscillations were analyzed by the Hilbert–Huang transform technique. The results showed that LLJs (≤14 m s −1 ) dominate at both Tianjin and Shanghai, with percentages of 76.5% and 84.8%, respectively. In terms of LLJ strength and frequency of appearance, evident diurnal changes were detected at the two sites, and nocturnal LLJs overwhelmed daytime LLJs in both strength and frequency. Influenced by the local topography and synoptic forcing, the LLJs were characterized by totally different distributions of wind directions and heights. The preferred direction at Shanghai was from the southwest and east, whereas northeast and south directions dominated at Tianjin. In the matter of jet heights, LLJs at Shanghai tended to occur at more consistent levels (56.3% of observed LLJs below 600 m) than at Tianjin. The LLJ wind-speed shear at Shanghai was also stronger than that at Tianjin. The Hilbert–Huang transform technique was applied to reveal the intrinsic mode functions with cycles of local inertial oscillation (19 h for Tianjin and 23 h for Shanghai), and the patterns of inertial oscillation power agreed with the time–height distribution of the observed LLJs.

Description: A specific question about the Himalayas is whether the orogeny grew by distributed extrusion or discrete thrusting. To place firm constraints on tectonic models for the orogeny, kinematic, thermobarometric and geochronological inverstigations have been undertaken across the Greater Himalayan Crystalline Complex (GHC) in the Nyalam region, south-central Tibet. The GHC in this section is divided into the lower, upper and uppermost GHC, with kinematically top-to-the-south, alternating with top-to-the-north shear senses, respectively. A new thrust named the Nyalam thrust is recognised between the lower and upper GHC, with a 3 kbar pressure reversion, top-to-the-south thrust sense, and was active after the exhumation of the GHC. Peak temperature reached ~749°C in the cordierite zone, and decreased southward to 633-667°C in the kyanite and sillimanite-muscovite zones, and northward to greenschist facies at the top of the South Tibetan Detachment System (STDS). Pressure at peak-temperature reached a maximum value in the kyanite zone of ~9.0-12.6 kbar and decreased northward to ~4.1 kbar in the cordierite zone. Zircon U-Pb ages of a sillimanite migmatite and an undeformed leucogranite dyke cutting the mylonitized rocks in the STDS reveal a long-lived partial melting of the GHC, which initiated at c . 39.7-34 Ma and ceased at 14.1 Ma. Synthesizing the obtained and collected results, a revised channel flow model is proposed by considering the effect of heat advection and convection by melt and magma migration. Our new model suggests that distributed processes like channel flow dominated during the growth of the Himalayan orogen, while discrete thrusting occurred in a later period as a secondary process. © 2013 Blackwell Publishing Ltd