A numerical study of mountain waves in the upper troposphere and lower stratosphere 1School of Mathematical and Statistical Sciences, Center for Environmental Fluid Dynamics, Arizona State University, Tempe, USA
01 Jun 2011
2Department of Meteorology and Geophysics, University of Vienna, Vienna, Austria
Received: 21 December 2010 – Published in Atmos. Chem. Phys. Discuss.: 08 February 2011 Abstract. A numerical study of mountain waves in the Upper Troposphere and Lower
Stratosphere (UTLS) is presented for two Intensive Observational Periods
(IOPs) of the Terrain-induced Rotor Experiment (T-REX). The simulations use
the Weather Research and Forecasting (WRF) model and a microscale model that
is driven by the finest WRF nest. During IOP8, the simulation results reveal
presence of perturbations with short wavelengths in zones of strong vertical
wind shear in the UTLS that cause a reversal of momentum fluxes. The spectral
properties of these perturbations and the attendant vertical profiles of heat
and momentum fluxes show strong divergence near the tropopause indicating
that they are generated by shear instability along shear lines locally
induced by the primary mountain wave originating from the lower troposphere.
This is further confirmed by results of an idealized simulation initialized
with the temperature and wind profiles obtained from the microscale model.
For IOP6, we analyze distributions of O3 and CO observed in aircraft
measurements. They show small scale fluctuations with amplitudes and phases
that vary along the path of the flight. Detailed comparisons between these
fluctuations and the observed vertical velocity show that the behavior of
these short fluctuations is due not only to the vertical motion, but also to
the local mean vertical gradients where the waves evolve, which are modulated
by larger variations. The microscale model simulation results show favorable
agreement with in situ radiosonde and aircraft observations. The high
vertical resolution offered by the microscale model is found to be critical
for resolution of smaller scale processes such as formation of inversion
layer associated with trapped lee waves in the troposphere, and propagating
mountain waves in the lower stratosphere.
Revised: 18 May 2011 – Accepted: 20 May 2011 – Published: 01 June 2011
Citation: Mahalov, A., Moustaoui, M., and Grubišić, V.: A numerical study of mountain waves in the upper troposphere and lower stratosphere, Atmos. Chem. Phys., 11, 5123-5139, doi:10.5194/acp-11-5123-2011, 2011.