Analysis of local wind induced by surface heterogeneity and sloping terrain near Nakdong river

Abstract

Local wind near river has been analyzed using data collected from nine automatic weather stations (AWS) and two flux stations near Gumi Weir, Nakdong River, for one year. Different onset time of river breeze at east and west river sides and spatial extension of divergent flow suggest that local wind at study area is generated by both the sloping terrain and the differential heating between the river and the land. Divergent (Convergent) flow is observed over the river during the daytime (nighttime). Wind divergence during the daytime is largest in summer and smallest in winter. Weak wind speed and large temperature difference in summer provide favorable condition for wind divergence. The strength of the divergent flow decreases rapidly with increasing wind speed for winds perpendicular to the river. The energy balance closure is evaluated by calculating the seasonal energy balance ratio (EBR), which at two flux sites ranges from 0.43 to 0.60 with the maximum in summer and the minimum in winter. To examine the influence of local circulation on EBR, we calculate the EBR in terms of divergence during the daytime in summer. The mean EBR in the large divergence case is lower than that in the small divergence case by 0.04 and 0.01 at west and east of river, respectively, indicating that local circulation is not main cause for low EBR at these sites.