Spatial-temporal characteristics of tornadoes in China based on observational data of meteorological stations

Tornadoes are the most destructive meso-small-scale strong convective weather on Earth. At present, however, the temporal change of tornadoes in a subcontinental region like mainland China is still controversial. Here, we report an analysis of the spatial-temporal pattern and long-term trend of tornadoes in mainland China from 1961 to 2013 based on a dataset of the national meteorological observational network. In total, 1082 tornado days were recorded by the national meteorological stations from 1961 to 2013, with an average occurrence frequency of 20.42 d yr-1. Three high-frequency centers are concentrated in South China, East China, and Northeast China. Tornadoes mainly occur in the summer season, mostly in July and August. The annual mean tornado days in mainland China during 1961-1969 reached 43.89 d yr-1, but the period 2010-2013 saw no tornadoes based on station records. There was a highly significant decreasing trend in annual total tornado days during 1961-2013, with a rate of -10.00 d per decade. The decreasing trend in summer was the most significant. We found that the decadal decrease in several atmospheric variables, including convective available potential energy, 0-6 km vertical shear, and low-troposphere relative humidity, is closely associated with the substantial decrease in the number of tornado days.