Abstract:

For finding out the interaction of land and atmosphere in semi － arid Loess Plateau，and taking the Dingxi of Gansu Province
as an example，the land surface characters on clear days in summer was simulated by MM5 Model． The simulated results were com-
pared with the observation data at the experimental station in Dingxi． Firstly，it was found out that the simulated temperature，soil heat
flux，radiation and sensible heat flux were similar to the observations，while the simulated moisture，ground temperature and latent heat
flux differed bigger from the observations． Secondly，the time of the highest value of ground temperature appearing in a day was 3 hours
earlier than the daily maximum air temperature in summer fine day in Dingxi，while the lowest value appeared at the same time． The air
moisture was lower，and the changes of specific humidity and dew condensing happened at the same time at night． The soil temperature
displayed obvious daily variations at the depth of 10 cm，but not at 40 cm and 80 cm． The soil heat flux showed typical daily changes
with single peak value at 13:00，and the maximum value of the solar shortwave radiation and the surface reflection radiation appeared
at the same time． The sensible heat flux was significantly greater than the latent heat flux in semi － arid area，so the primary heat flux
was mainly the sensible heat flux in semi － arid area． The highest value of the boundary layer height was up to about 2 100 m，which
was 1 000 m lower than that of Dunhuang in arid area．

Key words: MM5 model, land surface characters, clear day in summer, loess plateau, semi － arid area

摘要：

以甘肃定西为例，利用中尺度模式 MM5 模拟了黄土高原半干旱区夏季晴天的陆面特征，并与观测资料进行对比分析。结果表明，对气温、土壤热通量、辐射、感热通量的模拟结果与观测比较一致，而对比湿、地表温度、潜热通量的模拟结果与观测偏差稍大。夏季晴天，定西地区的地表温度日最高值出现时间较日最高气温出现时间早了 3 h，但两者日最低值出现时间相同;10 cm 深度处的土壤温度存在明显的日变化，而 40、80 cm 深度处无明显的日变化;空气湿度较低，夜晚比湿的变化与露水的凝结量变化时间一致;土壤热通量呈典型的单峰型日变化特征，日最大值出现在 13:00，与太阳短波辐射与地表反射辐射日最大值出现的时间相同;在半干旱区感热通量明显大于潜热通量，热通量以感热通量为主;边界层高度最高可达到 2 100 m 左右，比干旱区敦煌的低 1 000 m 左右。

关键词: MM5, 陆面特征, 夏季晴天, 黄土高原半干旱区