Model representation of a downslope windstorm in north-west Iceland

Hodder, Wilhelm (2023) Model representation of a downslope windstorm in north-west Iceland. Doctoral thesis, University of East Anglia.

Preview

PDF Download (33MB) | Preview

Abstract

The role of turbulent exchange of heat and moisture in the lee of mountains is not well understood, and these processes are generally not resolved or parametrised in numerical weather prediction (NWP) models.
High resolution Met Office Unified Model (MetUM) simulations are run and compared to in-situ observations from 12th and 19th March 2018 over Snæsfellsnes peninsula and the Westfjords, in north-western Iceland. With sub-kilometre horizontal grid-scales flow features – such as a downslope windstorm coupled with a hydraulic jump and a wave-breaking region directly aloft – are well resolved and provide suitable cases for testing different MetUM science configurations. The model simulations have been evaluated against aircraft observations, as well as radiosonde and ground-based observations and the 0.5-km horizontal grid-spacing simulation is found to reproduce the resolved features with reasonable fidelity. As a result, the 0.5-km simulation has been established a suitable truth for model sensitivity studies.
A detailed case study analysis of a downslope windstorm over a meso-scale ridge on the 19th March 2018 is conducted and shows that the reproduction of the event is highly sensitive to resolution and is not represented in the global driving model. Analysis of the downstream impacts of the 0.5-km simulation compared to the 4.4-km and global simulations shows large lee-side differences nearest to the slope, but these differences generally attenuated to background levels within 140 km. Changing the default boundary layer turbulence parametrisation for one employing a long-tailed stability function produced similar differences seen in the resolution-sensitivity.
An 11-year climatology using the Copernicus Arctic Reanalysis (CARRA) is conducted to place the case study event into climatological context and to investigate the downstream impacts of these events on the large-scale flow. The event is found to be a moderate event for the region and time-averaged composites revealed weak, but consistent wake signatures.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Nicola Veasy
Date Deposited:	25 Oct 2023 10:12
Last Modified:	25 Oct 2023 10:12
URI:	https://ueaeprints.uea.ac.uk/id/eprint/93467
DOI:

Downloads

Actions (login required)

View Item