ACINN Graduate Seminar - SS 2023

2023-06-07 at 12:00 (on-line and on-site)

Valley floor inclination affecting valley winds and transport of passive tracers in idealised simulations

Johannes Mikkola

Institute for Atmospheric and Earth System Research, University of Helsinki


The effect of the valley shape on the valley winds has been studied by numerous measurement campaigns and modelling studies, using both real and idealised topographies. In this work we further investigate the effect of the valley floor inclination on the daytime valley wind strength and transport of passive tracers out from the valley by means of idealised WRF-simulations (Weather Research and Forecasting model).

The analysis consists of four idealised valley topographies with a sinusoidal shape in the cross-valley direction and the along-valley inclination is constant throughout the valley. Four valleys, each 100km long and 2km deep, are simulated. One of the valleys has a flat valley floor and in three of the valleys the floors are inclined to reach 1km (0.57 degrees), 2km (1.14 degrees) and 4km (2.28 degrees) height along the 100km valley length. Passive tracers are released near the surface at different locations in along-valley and cross-valley direction and at different times of the day to simulate the effect of different emission sources.

The daytime up-slope winds are mostly responsible for the ventilation of the tracers whereas the along-valley winds transport the tracers towards the valley top within the valley atmosphere. For the inclined cases, the total amount of tracers transported out of the valley is smaller compared to the flat floor valley but the ventilation occurs at higher altitudes with increasing inclination.




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