Observation and modelling of variability in flow over complex terrain

Barkwith, AKAP

Abstract

This thesis examines the way in which remote sensing instrumentation can be used to
advance our understanding of the interactions between complex terrain and the
atmospheric boundary layer (ABL). When mean flow speed is of moderate strength and
the ABL is stable, mechanical effects will dominate thermal effects in modifying flow
speed and direction. Boundary layer measurements were made using the scanning
Salford 10 micron pulsed CO2 Doppler lidar during the 2005 Convective Storm Initiation
Project (CSIP), above the heterogeneous orography that surrounds Faccombe,
Hampshire, UK. A new method of detecting boundary layer flow perturbations was
developed, and successfully applied to the lidar data, giving a clearer insight into flow
modification that occurs above complex terrain.
The observations are compared to the output from a simple one dimensional boundary
layer flow prediction numerical model, and the three dimensional Computational Fluid
Dynamics model (CFD), WRF (Weather Research and Forecasting). Reasonable
correlation was found between the lidar data and the simple model output; however, the
model results are spatially limited and have many associated assumptions, which are
discussed. The WRF model was found to be adequate at predicting flow differences at
lower altitudes, outputting well defined structures consisting of perturbed flow.
However, this model tended to under predict the details of flow difference at higher
altitudes in comparison to the CSIP lidar observations. The inability of WRF and similar
CFD models to predict the detailed effects of orographically induced variation on upper
level ABL flow is of concern, as the inaccuracies affect the performance of such models
in reproducing flows on scales of importance in forecasting local weather and pollutant
dispersion.

Citation

Barkwith, A. Observation and modelling of variability in flow over complex terrain. (Thesis). Salford : University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2009