西北地区东部季风摆动区大气边界层高度对夏季风活动和季风降水的响应特征

Response characteristics of atmospheric boundary layer height to summer monsoon activity and monsoon precipitation of monsoon swing region in the eastern part of northwest China

大气边界层高度影响着近地层能量、水分的发展变化,而季风摆动区边界层受夏季风活动和季风降水影响很大,变化特殊,但其边界层高度的响应特征并不清楚。应用西北地区东部5站民勤、榆中、平凉、银川和延安2006-2016年5~9月逐日19时每隔10 m高度高空加密观测资料,以及民勤2006-2016年逐日07时探空规定层和特性层资料,结合地面逐日观测资料,对比计算多种资料找到合适的边界层高度。进一步运用NCEP、EC再分析资料,分析夏季风对季风摆动区的影响,得出边界层高度与夏季风、季风期降水影响的关系。结果表明:基于每隔10 m加密压温湿风探空资料,确定了9点平均位温梯度法作为边界层高度的最佳计算方法,该区边界层高度5~6月较高,7~9月逐渐降低,5~9月平均高度由非季风影响区的2600 m、季风摆动区的1800 m逐渐降低到季风影响区的1500 m以下。边界层高度与地面相对湿度、地温和风场关系密切,湿度越大、风速越大,边界层高度越低,相反,近地面地气温差越大,气温越高,吹西北风时,边界层高度越高。在不受夏季风影响时,边界层高度较高,有夏季影响风时,边界层高度较低。夏季风持续时间越长,边界层高度越低,当夏季风持续时间为0候、1~4候和≥5候时,边界层高度分别为2000 m左右、1600~1900 m和1300~1400 m。APO季风强度指数与季风影响区边界层高度有显著的负相关,APO季风强度指数越大,季风影响区边界层高度越低。边界层高度与季风期降水性质、强度关系较为密切,从大到小为无降水、对流性降水和稳定性降水;随着降水强度增强,边界层高度降低,边界层高度中非季风影响区较高,季风摆动区次之,季风影响区最低。降水日数越多,边界层高度越低。夏季风反过来对降低边界层高度,增多增强季风期降水起着积极作用。

The atmospheric boundary layer height(BLH)affects near-grounddevelopment of energy and water.The boundary layer of the monsoon swing area in the eastern part of northwest China is significantly affected by summer monsoon activity and monsoon precipitation;however,its changes and the response characteristics of the BLH are not clear.A suitable BLH was determining by comparing calculations using many kinds of methods.These calculations used daily upper observation data collected every 10 m at 19:00 from five stations(Minqin,Yuzhong,Pingliang,Yinchuan,and Yan’an)in the summer monsoon swing areafrom May to September during 2006-2016 in addition to the prescribed and characteristic layers of daily sounding data at 07:00 in Minqin during 2006-2016 as well as daily surface observation data during the corresponding period.Then,using NCEP/EMC reanalysis data,the influence of summer monsoon on the monsoon swing area’s BLH was calculated and analyzed,and the relationships between BLH and the summer monsoon and precipitation effects during the monsoon activity period was obtained.The results showed thatthe 9-point mean temperature gradient method was the best BLH calculation methodbased on the sounding data of pressure-temperature-humidity and wind every 10 m.The BLH in this area was higher in May and June and decreased gradually from July to September.The average BLH decreased from 2600 m in the non-monsoon region and 1800 m in the monsoon swing area to less than 1500 m in the monsoon affected area.The BLH is closely related to relative humidity,temperature,and wind field at the surface,with higher humidity and wind speed yielding a lower BLH.In contrast,a greater near-ground temperature difference and higher temperature yields a higher BLH when the northwest wind blows.The BLH was higher when there was no summer monsoon and lower when there was a summer monsoon.The longer the duration of the summer monsoon was,the lower was the BLH.When the duration of the summer monsoon was 0,1-4,and≥5 pentads,the corresponding BLH values wereapproximately 2000 m,1600-1900 m,and 1300-1400 m.There was also a significant negative correlation between the APO monsoon intensity index and BLH in the monsoon affected area.The BLH was closely related to precipitation properties and intensity during the monsoon activity period,with non-precipitation,convective precipitation,and stable precipitation having effects in turn from large to small.The BLH decreased with increasingprecipitation intensity,and the BLH was higher in the non-monsoon area,lower in the monsoon swing area,and the lowest in the monsoon affected area.Additionally,more precipitation days were associated with a lower BLH.The summer monsoon played an active role in lowering BLH and increasing and strengthening precipitation during the monsoon period.