Storage and transport processes in an idealized valley with a LES reference

Trace gas simulations and inverse modelling on the regional scale require an accurate representation of atmospheric boundary layer (ABL) processes. Thus, complex terrain, such as the Swiss Midlands, poses challenges like uncertainties in local turbulent transport, advection, and diffusion. Current operational numerical weather prediction models still provide limited accuracy for the simulation of vertical mixing processes over such regions. Horizontal transport and vertical mixing in the ABL induced by local circulations directly impacts the vertical profiles of trace gases emitted at the surface. A bias in these processes may introduce significant errors in the estimate of trace gas concentrations, especially for the accumulation of greenhouse gases (GHG) during nighttime stable conditions. Since the potential sources of error in representation of stable boundary layers (SBL) include the boundary layer scheme and numerical mixing, an accurate representation of vertical mixing of trace gases in all types of boundary layers is needed. Therefore, in the present work, high-resolution simulations using Cloud Model 1 (CM1) in Large Eddy Simulation (LES) configuration and with idealized topography, representative of the rolling terrain around the tall tower at Beromünster, are performed. This study contributes to an improved understanding of the relevant storage and transport processes of accumulation of passive tracer in nocturnal cold pools, and their morning depletion, along with sensitivities to initial atmospheric stratifications and upper-level wind. The model setup also includes virtual towers located at valley floor, over the slope and the mountain ridge. Together with the sensitivity experiments, along-valley, time averaged model outputs will be presented.