基于自动站观测的北京夏季降水特征

应用2007~2011年北京地区237个自动气象站资料,分析了北京夏季降水的精细化时空分布特征及城郊差异,结果表明:(1)北京大部分地区夏季平均有效降水时数约120~160 h,降水时数高值区主要位于北部怀柔、密云山前迎风坡一带。城、郊区间有效降水时数差异并不明显,城市化对局地降水强度有较明显影响。(2)北京夏季降水主要出现在傍晚到前半夜,凌晨到正午降水较少出现。夏季平均降水量极大值出现在17:00(北京时间),为3.2 mm/h。降水量存在较明显的周期变化特征,其中7 d左右的周期是主周期。(3)夏季城区平均降水量多于郊区,城、郊雨量差异主要来自较强降水过程。城市效应会导致城区弱降水事件的减少,亦会导致较强降水事件的增多。(4)城、郊区间降水持续时长的差异主要由较强降水过程决定,多数情况下城区降水持续时长大于郊区,午后到前半夜发生的降水尤甚。

Statistical Characteristics of Precipitation in Summer in Beijing Area during 2007-2011

Using hourly precipitation data from 237 automatic weather stations in Beijing area from June to August 2007-2011, the fine-scale spatiotemporal distribution of precipitation and the effect of the city on local precipitation in Beijing were studied. Based on the analysis, the major findings can be summarized as follows: Firstly, in most areas of Beijing, the average number of effective precipitation hours in summer was between 120 h and 160 h. The maximum value of effective precipitation hours was recorded in the piedmont windward area in the north of Beijing. The difference in effective precipitation hours between urban and suburban areas was not obvious, and the main impact of urbanization was on precipitation intensity. Secondly, summer precipitation in Beijing occurred mainly in the evening until midnight; from midnight to noon there was less precipitation. The average annual rainfall maximum appeared at 1700 LST reaching 3.2 mm/h. Furthermore, there was an obvious precipitation cycle, for which the main length of the period was about seven days. Thirdly, the differences in precipitation between urban and suburban areas were mainly caused by heavy rainfall, with urbanization leading to a reduction in weak precipitation events but a strong increase in precipitation events as a whole. Finally, the differences in continuous precipitation hours between urban and suburban areas was determined mainly by heavy rainfall; in most cases, the duration of precipitation was higher in the suburbs, occurring most commonly in the period from afternoon to midnight.