兰州近50a冬季气温变化及其可能原因分析

利用1960—2010年兰州等3站逐日观测资料，分析了兰州冬季气温变化及其可能成因。结果表明：近50 a兰州冬季气温、日较差、冷日数、冷积温及极端高、低温日数的变化速率均在1980s发生跃变。平均气温持续显著的增温，在1960s、1970s最低气温增温起主要作用，日较差、冷积温及极端低温日数显著减少，在1980s后由最低、最高气温共同增温所致，日较差减小变缓，冷积温稳定维持在较低水平，极端高温日数显著增加。大气环流异常和城市化共同影响，导致兰州冬季显著增温，二者对增温的贡献率分别约为37.24%和62.76%。1980s中期之后中高纬度欧亚上空对流层中层盛行纬向环流，两槽一脊的振幅减弱，西北地区位于中国上空异常反气旋西部偏南气流控制下，且同期城市热岛效应更加显著，这些均有利于兰州冬季增温。

Change of winter temperature and its possible causes in Lanzhou during the recent 50 years

Based on the daily observation data of observation stations including Lanzhou,Yuzhong,Gaolan during 1960-2010,the change trends and characteristics of winter air temperature and its possible causes were analyzed. The main results show that the change rate of air temperature, daily range, cold accumulated temperature and extreme temperature days of winter in Lanzhou made a abrupt change in the 1980s.The mean temperature had an overall significant increasing trend,which mainly resulted in the increasing of the minimum temperature in the 1960s and 1970s.Daily range,cold accumulated temperature and extreme minimum temperature days decrease signficantly, which were caused by minimum temperature and maximum temperature warming after the 1980s. Meanwhile,daily range reduced slowly;cold accumulated temperature maintained stable at low levels;extreme maximum temperature days increased significantly.The significant increase of winter temperature in Lanzhou was caused by urbanization and atmospheric circulation anomalies,which accounted for 62.76% and 37.24% respectively. With the prevailing of zonal circulation in the middle of troposphere in extratropics over the continent of Europe and Asia after the mid-1980s and the weakening of trough-ridge-trough,Northwest China is effected by the anomalous south airflow, which located the western anomalous anticyclonic over China. Meanwhile, the urban heat island effect is more significant over the same period.These are all conducive to winter warming in Lanzhou.