Frost injury has great influence for tropical and subtropical crops in Fujian.Such crops possess poor ability to resist cold air,and so studying their frost injury characteristics is extremely important for disaster prevention and reduction.Firstly,based on daily meteorological observational data at 68 stations over Fujian from January to April and from October to December (1981-2011),an index of frost injury in Fujian is determined,by combining the lowest ground surface temperature,weather phenomena,and lowest temperature.Frost injury is defined by any one of these three conditions as follows:the lowest ground surface temperature is lower than or equal to 0 ℃;frost or freezing is found on the ground surface;and the lowest temperature is lower than or equal to 2 ℃.The climatic characteristics are investigated and discussed.The basic conclusions are as follows: (1)The annual average number of frost injury days,the first and last frost injury date,and the number of frost injury-free days in Fujian demonstrate obvious regional differences,with northeast-southwest-trending contours that correlate well with metrological station elevations.The whole province of Fujian is divided into three frost injury regions.The western and northern regions and high elevation mountain area belong to region I,where frost injury occurs easily,begins earlier,ends later,and there are fewer frost injury-free days.Region III encompasses hilly landscapes in coastal areas,seldom effected by frost injury.The regional averages of the first and last frost injury date in regions I and II,respectively,show delayed and advanced trends,while the number of frost injury-free days increase. (2)Frost injury over most areas of Fujian with short duration is uncommon,and its occurrence frequency becomes lower and lower. (3)By comparison of frost injury with different intensity,it shows that the stronger frost injury takes more widespread damage,occurs later,and finishes earlier,with less number of frost injury days.The circulation background leading to frost injury in Fujian is also discussed,based on NCEP/NCAR four-times-daily reanalysis data during the same period.It is found that the meridional circulation increases at the level of 500 hPa,the line of 568 dagpm goes through the south of Zhejiang Province,and the upper cold center intensity at -36 ℃ stays behind the East Asian trough,with strong cold advection.The line of 0 ℃ on the 850 hPa layer moves southwards close to Fujian Province.On the surface layer,most areas of East China are controlled by cold high pressure at 1 029 hPa.In this circulation background,the weather is relatively fine in Fujian,but then the temperature plummets owing to surface radiation at night,so frost injury occurs easily.Through analysis of the circulation characteristics at 0800 BT on the day of beginning and the next day of ending with different frost injury intensity,it is found that the position of the index lines,such as the lines of 568 dagpm (500 hPa),0 ℃ (850 hPa),1 025 hPa (surface layer) and so on,is closely related to the frost injury intensity.Frost injury strengthens gradually along with the index lines moving southward,and vice versa.The index lines move less significantly in the period from medium-strength to high-strength,as compared to during the period from low-strength to medium-strength.