Abstract: The late Prof. Li Xianzhi (Dr.Sjan-zsi Li) was a professor with Peking University and a famous meteorologist in China. In his youth, he took part in The Scientific Expedition to China's Northwestern Provinces during 1927-1930. He observed the movement of a strong outbreak of cold air masses in late Oct. 1928, in Qinghai Province. This event had an important influence on Li Xianzhi's life. Between 1930 and 1936, he studied and then worked in Berlin University. He published his famous papers "A Study on the Outbreak of cold air in East Asia" and "A Study on Typhoon" in 1934 and 1936 respectively. He got a Doctor's Degree in 1934 and came back to his motherland in 1936. He devoted himself to the teaching of meteorological sciences in China's famous institutions of higher learning i.e., Tsinghua and Peking universitie, and to meteorological studies. He wrote quite a number of initiative works. He discovered that cold air coming from the North Pole region can sweep across the Equator and then reach the Southern Hemisphere, and lead to precipitation and drops in temperature over there. At the same time, he pointed out that the outbreak of cold air coming from Australasia can lead to the generation of typhoon in the northwestern Pacific when the cold air crosses the Equator and reaches the lower latitude regions of the Northern Hemisphere. In the later part of his life, Li Xianzhi presented a new concept of "Microscopical System between two Hemispheres". He pointed out that the heavy rainfall and flood disasters on the Chinese mainland are closely connected with the weather systems coming from the Southern Hemisphere. This theory points a new way to the monitoring and prediction of heavy rainfall and flood disasters in China. This paper presents a comprehensive study and comment on Prof. Li Xianzhi's principal research results and his viewpoint on the study of meteorological disasters, and shows his influence and his contribution.

Key words: Expedition to Northwestern Provinces of China, outbreak of cold air in East Asia, generation of typhoon, macroscopical system between two hemispheres, monitoring and prediction of meteorological disasters

摘要： 李宪之是我国著名气象学家，北京大学教授。他年轻时（1927—1930年）参加了中国西北科学考查团，在青海亲历了一次强大寒潮的侵袭，对其一生有重要的影响。1930—1936年赴德国柏林大学学习和工作。1934年获博士学位，1936年回国。历任清华大学、西南联大及北京大学教授。李宪之先生一生从事气象高等教育及科学研究，有许多开创性的工作。1934—1936年先后发表了《东亚寒潮侵袭的研究》和《台风的研究》，发现东亚寒潮可以穿越赤道，到达南半球并在那里引发降温与降水，同时提出了南半球澳洲大陆寒潮的爆发可以越过赤道在西北太平洋引发台风的生成。晚年又提出了“宏观系统”的概念，指出中国大陆特大暴雨的发生主要与来自南半球的天气系统有着重要的联系，从而提出了对中国特大暴雨及洪涝灾害可以进行监测与预测的理论。本文综合介绍了他在气象灾害研究方面的主要观点、成果以及对气象科学研究的影响与贡献。

关键词: 中国西北科学考查团, 东亚寒潮侵袭, 台风生成, 半球间宏观系统, 气象灾害监测与预测