Along-Valley Structure of Daytime Thermally Driven Flows in the Wipp Valley

High-resolution Doppler lidar observations obtained during the Mesoscale Alpine Program (MAP) 1999 field campaign are used to investigate the along-valley structure of daytime valley flows in the Wipp Valley, Austria. The observations show that under varying ambient conditions the valley flow increases in speed through a narrow section of the valley. Furthermore, the along-valley volume flux diverges along the valley segment under investigation, which suggests that the observed along-valley acceleration of the valley flow cannot be explained by the horizontal constriction of the valley sidewalls. It is hypothesized that the along-valley acceleration of the flow is caused by an intravalley change in the horizontal pressure gradient induced by differential heating rates of the valley atmosphere.