The annual and decadal variations, anomalous and abrupt change of the frost days are analyzed in this paper, using the daily minimum temperature of 38 stations over Tibet from 1981 to 2010 and modern statistical diagnosis methods, such as linear trend analysis, accumulative anomaly, signal noise ratio and rescaled range analysis (R/S analysis). The results showed that, (1) in recent 30 years, the frost days decreased with a rate of (3.3-14.6) d/ 10a (P<0.01, at 37 stations), and the damping of frost days increased with increasing altitude. (2) In terms of decadal variations, the frost days presented a negative anomaly in the 1980s and a positive anomaly in the 2000s, the positive anomaly range of frost days was larger than the negative anomaly in the 1990s. (3) It was found with abrupt change test that frost days at eight stations had abrupt change, which occurred in the 1990s with the year 1997 having the largest number. (4) The results of R/S analysis showed that changes of frost days had the persistence with a Hurst index larger than 0.5 at most of the stations, and indicated that it will assume a continuous decrease in future and the decreasing rate will became larger. (5) In addition, it was found that the frequency of anomalous (more than normal) frost days was 0 to 3 times and occurred mainly in the 1980s, while the anomalous (less than normal) frost days occurred in the 2000s with a frequency of 0 to 4 times. There is little correlation between altitude (or latitude, longitude) and anomalous more frost days frequency, while altitude has negative correlation with anomalous less frost days frequency.
[1] IPCC. Summary for Policymakers of Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2007.
[2] China Meteorological Administration. Climate and Environment in China. Beijing: China Meteorological Press, 2006.[中国气象局. 中国气候与环境演变. 北京: 气象出版社, 2006.]
[3] Yao Tandong, Liu Xiaodong, Wang Ninglian. Amplitude of climatic change in Qinghai-Tibetan Plateau. Chinese Science Bulletin, 2000, 45(1): 98-106. [姚檀栋, 刘晓东, 王宁练. 青藏高原地区的气候变化幅度问题. 科学通报, 2000, 45(1): 98-106.]
[4] Wei Zhigang, Huang Ronghui, Dong Wenjie. Interannual and interdecadal variations of air temperature and precipitation over the Tibetan Plateau. Chinese Journal of Atmospheric Sciences, 2003, 27(2): 157-170. [韦志刚, 黄荣辉, 董文杰. 青藏高原气温和降水的年际和年代际变化. 大气科学, 2003, 27(2):157-170.]
[5] Xu Zongxue, Zhang Ling, Huang Junxiong et al. Long term trend of temperature, precipitation and relative humidity in the Tibetan region. Meteorological Monthly, 2007, 33(7): 82-88. [徐宗学, 张玲, 黄俊雄等. 西藏地区气温、降水及相对湿度的趋势分析. 气象, 2007, 33(7): 82-88.]
[6] Wu Shaohong,Yin Yunhe, Zheng Du et al. Climate changes in the Tibetan Plateau during the last three decades. Acta Geographica Sinica, 2005, 60(1): 3-11. [吴绍洪, 尹云鹤, 郑度等. 青藏高原近30 年气候变化趋势. 地理学报, 2005, 60 (1): 3-11.]
[7] Liu Xiaodong, Hou Ping. Relationship between the climatic warming over the Qinghai-Xizang Plateau and its surrounding areas in recent 30 years and the elevation. Plateau Meteorology, 1998, 17(3): 245-249. [刘晓东, 侯萍. 青藏高原及其邻近地区近30 年气候变暖与海拔高度的关系. 高原气象, 1998, 17(3): 245-249.]
[8] Zhang Shunli. The characteristics of temperature change in Tibet in 1961-1990. Meteorological Monthly, 1997, 23(2): 21-24. [张顺利. 西藏30 年温度变化的气候特征. 气象, 1997, 23(2): 21-24.]
[9] Du Jun. Change of temperature in Tibet plateau from 1961 to 2000. Acta Geographica Sinica, 2001, 56(6): 682-690. [杜军. 西藏高原近40 年的气温变化. 地理学报, 2001, 56(6): 682-690.].
[10] Tan Chunping, Yang Jisnping, Mi Rui. Analysis of the climatic change characteristics in the southern Tibetan Plateau from 1971 to 2007. Journal of Glaciology and Geocryology, 2010, 32(6): 1111-1120. [谭春萍, 杨建平, 米睿. 1971-2007 年青藏高原南部气候变化特征分析. 冰川冻土, 2010, 32(6): 1111-1120.]
[11] Du Jun. Asymmetric change of maximum and minimum temperature in Tibetan Plateau from 1971 to 2000. Journal of Applied Meteorological Science, 2003, 14(4): 437-443. [杜军. 西藏高原最高、最低气温的非对称变化. 应用气象学报, 2003, 14(4): 437-443.]
[12] You Yuanlong, Kang Shichang, Yan Yuping et al. Trends in daily temperature and precipitation extremes over the Yarlung Zangbo River basin during 1961-2005. Acta Geographica Sinica, 2009, 64(5): 592-600. [游庆龙, 康世昌, 闫宇平等. 近45年雅鲁藏布江流域极端气候事件趋势分析. 地理学报, 2009, 64(5): 592-600.]
[13] Zhai Panmao, Ren Fumin. On changes of China's maximum and minimum temperatures in the recent 40 years. Acta Meteorologica Sinica, 1997, 55(4): 418-529. [翟盘茂, 任福民. 中国近四十年最高最低温度变化. 气象学报, 1997, 55 (4): 418-529.]
[14] Heino R, Coauthors. Progress in the study of climate extremes in northern and central Europe. Climatic Change, 1999, 42: 151-181.
[15] Bonsal B R, Zhang X, Vincent L A et al. Characteristics of daily and extreme temperature over Canada. J. Climate, 2001, 14: 1959-1976.
[16] Easterling D R. Recent changes in frost days and the frost-free season in the United States. Bull. Amer. Mete. Soc., 2002: 1327-1332.
[17] Zhai Panmao, Pan Xiaohua. Change in extreme temperature and precipitation over northern China during the second half of the 20th century. Acta Geographica Sinica, 2003, 58(9): 1-10. [翟盘茂, 潘晓华. 中国北方近50 年温度和降水极端事件变化. 地理学报, 2003, 58(9): 1-10.]
[18] Ma Guozhu. Variation of frost days and its relationship to regional warming in northern China. Acta Geographica Sinica, 2003, 9(Suppl.): 31-37. [马柱国. 中国北方地区霜冻日的变化与区域增暖相互关系. 地理学报, 2003, 9(增刊): 31-37.]
[19] Ye Dianxiu, Zhang Yong. Characteristics of frost changes from 1961 to 2007 over China. Journal of Applied Meteorological Science, 2008, 19(6): 661-665. [叶殿秀, 张勇. 1961-2007 年我国霜冻变化特征. 应用气象学报, 2008, 19(6): 661-665.]
[20] Han Rongqing, Li Weijing, Ai Wanxiu et al. The climatic variability and influence of first frost dates in northern China. Acta Geographica Sinica, 2010, 65(5): 525-532. [韩荣青, 李维京, 艾婉秀等. 中国北方初霜冻日期变化及其对农业的影响. 地理学报, 2010, 65(5): 525-532.]
[21] Li Fen, Zhang Jianxin, Wu Yongli et al. Spatial and temporal distribution and its impact factors of the last frost over Shanxi Province from 1961 to 2010. Acta Geographica Sinica, 2013, 68(11): 1472-1480. [李芬, 张建新, 武永利等. 近50 年山西终霜冻的时空分布及其影响因素. 地理学报, 2013, 68(11): 1472-1480.]
[22] Liu et al. Temporal trends and variability of daily maximum and minimum, extreme temperature events, and growing season length over the eastern and central Tibetan Plateau during 1961-2003. Journal of Geophysical Research, 2006, 111(19109), doi: 10.1029/2005JD006915.
[23] You et al. Relationship between trends in temperature extremes and elevation in the eastern and central Tibetan Plateau, 1961-2005. Geophysical Research Letters, 2008, 35(L04704), doi: 10.1029/07GL032669.
[24] You et al. Changes in daily climate extremes in the eastern and central Tibetan Plateau during 1961-2005. Journal of Geophysical Research, 2008, 113: D07101.
[25] Du Jun. Climate Characteristics and the Forecast Method Research of Frost over Tibetan Plateau. Beijing: China Meteorological Press, 2005. [杜军. 西藏高原霜冻气候特征及预报方法研究. 北京: 气象出版社, 2005.]
[26] Wei Fengying. Statistics Technology of Diagnose and Forecast of Modern Climate. Beijing: China Meteorological Press, 1999. [魏凤英. 现代气候统计诊断与预测技术. 北京: 气象出版社, 1999.]
[27] Chen Qianjin, Zhang Yongshan. Study on climatic features of unusual first and last frost in north China. Journal of Natural Disasters, 1995, 4(3): 33-39. [陈乾金, 张永山. 华北异常初终霜冻气候特征的研究. 自然灾害学报, 1995, 4 (2): 33-39.]
