Simulation of the meteorological conditions during a winter smog episode in the Inn Valley

Abstract

A state-of-the-art numerical non-hydrostatic model is applied to simulate meteorological conditions during a winter smog episode in a large Alpine valley. This case study illustrates what such models are capable of and where there are limitations. The PSU/NCAR mesoscale model known as MM5, version 3.7, is used to simulate the period 31 January 2004 until 9 February 2004, when elevated pollution levels were observed in the Inn Valley. The MM5 model was used with the modifications provided by G. Zangl and with two different boundary layer schemes. Simulation results of five different model runs are compared with wind and temperature observations in the valley, at mountain stations and outside the Alps. A comparison of the results of the runs using a resolution of 2.4 km in the innermost nest with a run with 0.8 km resolution shows that 2.4 km is insufficient for acceptable results, while with 0.8 km the characteristic features could be reproduced. This concerns mainly the temperature and stability inside the Inn Valley whereas conditions in the Alpine foreland are simulated reasonably even at the coarser resolution.