Atmospheric boundary layer wind field in the HEIFE area

Simultaneous wind data collected from micrometeorological tower stations and automatic weather stations have been used to investigate the principal features and seasonal variations of the wind fields in the HEIFE experimental area. Besides wind statistics from a less modified data set, a MASCON wind model was adopted in an objective investigation of the three-dimensional atmospheric boundary layer flow during IOP-2 and IOP-3. The results have shown that synoptic scale, mesoscale and sub-mesoscale motions play different roles in different places. Under strong wind conditions, a northwesterly wind is predominant in the area with significant features of mechanical constraint by the mesoscale topography. On fair weather days, the flow patterns exhibit strong diurnal and spatial variations. In the sites adjacent to the north slope of Qilian Mountain and along the valley axis, flows featuring thermal forcing by mesoscale terrain are apparent, but daytime flows show significant seasonal shifts due to the link with the synoptic winds. Around the northern part of the experimental area, diurnal variations of the flows show a more complicated site-dependent behavior, which is caused by the simultaneous influences of synoptic-scale wind and the flows induced by small-scale topography.