Atmospheric Heating Source Over the Tibetan Plateau and Its Regional Climate Impact

Abstract

With an average elevation of 4 kilometers, a combined area of more than 2.5 million square kilometers, and a variety of complicated landscapes, the Tibetan Plateau (TP) constitutes the highest and largest terrain on earth. The Tibetan and Iranian Plateau (TIP) form a dynamically coupled system that exerts a tremendous impact on the regional and global climate. The TIP’s geographic location in the subtropics of central and eastern Asia, along with its altitude, size, and steep terrain on the southern and eastern slopes, make this climate impact particularly unique. In winter, the TIP reacts to the impinging subtropical westerly flow, producing a strong negative mountain torque and forming a prominent stationary circulation dipole with a huge anticyclone circulation to its north and cyclone circulation to its south in the tropics. A specific winter climate pattern over Asia is thus formed. Due to its high elevation, the total mass of the air column over the TP is much smaller than over the neighboring regions, as the solar radiation heating in this region is more efficient. The atmospheric heating source (AHS) over the TP is negative in winter and strongly positive in summer. On this elevated terrain there is also a large number of intersecting isentropic surfaces in the lower troposphere. Along its sloping surfaces, the cooling in winter causes the near-surface air to slide downward and diverge toward its surroundings, whereas the surface heating of the slope in summer results in near-surface air ascent, causing the surrounding air to converge toward the plateau. More significantly, due to its huge size, the surface-sensible heating of the TIP produces a large-scale surface cyclonic circulation and works as an immense sensible-heat-driven air pump (SHAP), which transports abundant water vapor from ocean to land to support the Asian continental monsoon. In addition, the plateau’s heating produces a subtropical monsoonal meridional circulation and creates a large-scale air ascent background in subtropical Asia. Therefore, the Asian monsoon is the consequence of the seasonal change not only in land-sea thermal contrast but also in the thermal forcing of large-scale mountains. Since the 1980s, the near surface atmospheric warming amplitude over the TP has grown much larger than the global mean, and the changes in climate and AHS over the TP have already influenced the water resources, ecosystem services, mountain hazards, and livelihoods across and around the TP. Understanding the climate effect of the TP’s AHS is not only a key issue for climate dynamics, but can also help us to recognize the thermal forcing of other large-scale topographies, such as the Rockies and Andes Mountains, on the global climate in the framework of land-air-sea interaction. This article will introduce the effect of the TP’s AHS on the regional climate, with emphasis on the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM), in terms of the climatology, intra-seasonal oscillation, interannual variability, and decadal change. Controversies, challenges, and future perspectives on this topic will also be presented. Its informative content can be used as a professional reference for research scientists and professionals in the fields of meteorology, climate dynamics, environmental science, geography and geology, hydrology, and paleo-climatology. Most material presented here can also be helpful for non-specialists.