Abstract: Based on the meteorological data at 52 weather stations in Liaoning province from 1960 to 2009, the number of winter wind chill temperature days for the different levels was calculated using a winter wind chill temperature formula and its optimal classification standard for Liaoning province. Based on the winter wind chill temperature days, the study area was divided by a rotated experience orthogonal function (REOF) method, and its spatial distribution and trend were analyzed. The results show that it could be divided into four levels based on winter wind chill temperature in Liaoning province, and each level has different sub-regions. The study area could be divided into four regions for cold to slight wind chill level, while it is three regions for the other three levels, i.e. mild, moderate and severe levels. There is less number of winter wind chill temperature days in five cities around Liaodong peninsula, while there is more in the north and northeast of Liaoning province. The variation trends of winter wind chill temperature days for four levels are similar. The number of annual mean winter wind chill temperature days is higher during 1960-1985, while it is less during 1986-2009. There is an abrupt change in 1986 for winter wind chill temperature days.

Key words: Wind chill temperature, Rotated experience orthogonal function (EOF), Rotated experience orthogonal function (REOF), Variance contribution, Regionalization