Inter-decadal variability of Tibetan spring vegetation and its associations with eastern China spring rainfall

Using the Normalized Difference Vegetation Index of NOAA/AVHRR, the European Centre for Medium-Range Weather Forecast reanalysis and the Climate Prediction Center Merged Analysis of Precipitation data for the period 1982-1999, the relationship between the inter-decadal variability of spring (April May) vegetation over the Tibetan Plateau (TP) and spring rainfall over eastern China was investigated. The results show that when the vegetation over the TP increases in spring, the spring rainfall enhances to the north of the Yangtze River and reduces to the south of the river. This relationship is well supported by the feedback of vegetation to climate and the background atmospheric circulation changes. Corresponding to more vegetation over the TP in spring, the surface sensible heating increases and local air temperature at the surface and in the troposphere also increases. The air volume expands, and the divergence becomes dominant in high-level atmosphere over the TP, with an increase in the upper-tropospheric geopotential height. This indicates an upper-tropospheric intensified ridge over the TP in spring. The intensified ridge extends toward eastern China. An anomalous anti-cyclone appears over the TP and eastern China, with anomalous divergence in the upper troposphere and anomalous convergence in the lower troposphere. Meanwhile, an anomalous cyclonic circulation appears in the lower troposphere over the northern region of eastern China, accompanying with the local anomalous upward motion. Therefore, the spring rainfall enhances over these regions. To the south of the upper-tropospheric anomalous anti-cyclonic centre, however, the upper easterlies from the western North Pacific Ocean retard while reaching the southeast coasts of China. This may result in the upper-tropospheric anomalous convergence, with anomalous divergence and an anomalous anti-cyclonic circulation in the lower troposphere over southeastern China and its coasts. Consequently, the spring rainfall weakens over these regions. Copyright (C) 2009 Royal Meteorological Society