应用北京地区地面气象观测站1990-2004年1月的气温资料，分析了近15年北京冬季城市热岛的特征和变化趋势，也分析了城市热岛强度与地面气温的关系。结果表明：夜间城市热岛要强于白天，近15年夜间城市热岛具有增强趋势，而白天这样的趋势不明显。夜间月平均城市热岛强度与月平均气温正相关，气温高的年份，热岛强度相对也大，白天这种相关不明显。此外，对比分析了冬季强热岛和弱热岛的特征及其气象影响因子。结果表明：强热岛出现于夜间，白天热岛不明显；夜间强热岛出现和维持是多种因子综合作用的结果。白天日照充足的晴夜北京城郊地面风场很弱（≤2.0m/s），多个测站甚至出现静风，同时城区垂直方向近地大气层持续存在很弱（≤2.0m/s）的风场，甚至静风，城区320m高度以下持续存在大气逆温，有利于冬季强热岛的形成和维持。晴朗白天即使近地层大气风速维持在2.5m/s以下，城市热岛也会减弱消失，太阳辐射的加热作用所引起的郊区地面大气升温速率和幅度大于城区地面大气、大气稳定度的变弱以及城区大气逆温的消失是城市强热岛减弱并最终消失的重要原因。

Based on the data of 20 meteorological stations from 1990 to 2004, the characteristics of Beijing urban heat island in the last 15 years were analyzed. The results show that the UHI in the evening is stronger than that in the daytime. The UHI in the evening tends to get stronger year by year, but which is not obvious in the daytime. In the evening, higher the average monthly surface temperature is, stronger the average monthly UHI is. But in the daytime the correlativity is not so obvious. Furthermore, with the additional data got by two automatic meteorological stations and the 325m meteorological tower of LAPC, the characteristics and influencing factors of a strong UHI and a weak UHI in winter were analyzed contrastively. And the results show that the cooling rate of the suburban surface atmosphere is bigger than that of the urban surface atmosphere after sunset, which directly leads to the formation of the strong UHI. And the heating rate of the suburb surface atmosphere is bigger than that of the urban surface atmosphere after sunrise, which directly causes the weakening and disappearance of the strong UHI. In the clear night of the sunny day, the occurrence and maintenance of the weak wind (≤2.0m/s) below 100m and the inversion temperature below 320m have important effects on the formation and maintenance of the strong UHI. And in the daytime the solar radiation has most important effects on the weakening and disappearance of the strong UHI. It makes the suburban surface atmosphere temperature rise faster than the urban atmosphere temperature, and makes the inversion temperature disappear, and further makes the strong UHI weaken and disappear at about 2:00 p.m. in the end even if the wind maintains weak in the daytime.