The spatio-temporal distribution of thermodynamic forces at the land-atmosphere interface in China

Abstract

Correlation analysis and the complementary relationship model are used to indirectly measure and characterize the dynamic and thermodynamic properties at the land-atmosphere interface in China. Results show that thermodynamic forces driving the exchange fluxes of energy, water and carbon between the land surface and the overlying atmosphere are significantly enhanced along the mid-upper reaches of the Yangtze River basin around Sichuan Basin and the northern region of Heilongjiang. The thermodynamic forces exhibit a decreasing trend in southern Xinjiang and some regions of Yunnan. Low cloud cover was shown to be a significant factor leading to changes in thermodynamic properties at the land-atmosphere interface. Western Pacific Subtropical High (WPSH) and storm data provide strong evidence that a changing synoptic system is likely a principle factor causing the abnormal spatiotemporal distribution of thermodynamic forces over the land surface in China. This data also suggests that cyclical and quasi-cyclical fluctuations of low cloud cover in most regions of China are responsible for annual rainfall patterns. At the same time, NOAA-AVHRR satellite remote sensing data illustrates that changes to land surface characteristics may cause atypical spatiotemporal distributions of thermodynamic forces over the land surface. We show that thermodynamic forces are weakening in regions with increasing vegetation. However, where urbanization has decreased the quantity of vegetation, thermodynamic forces are rising. Finally, an increase in large-scale thermodynamic forces is associated with a reduction in low cloud cover due to changes in the synoptic system.