Stratocumulus predictions with a Large-Eddy Simulation Model

Stratocumulus predictions with a Large-Eddy Simulation Model

Heuff, F.M.G.

De Roode, S.R. (mentor)

Civil Engineering and Geosciences

Geoscience and Remote Sensing

2016-01-28

In this study the prediction of stratocumulus occurrence by the Large-Eddy Simulation model DALES was investigated. The performance of DALES was compared with that of the large-scale weather model RACMO. A method was developed which can consistently initialise the model by assimilation of observations in addition to large-scale weather model results. This method was then applied to four days in winter on which stratocumulus occurred. The results were analysed with the use of the liquid water path (LWP) budget analysis, which analyses the contributions of the relevant processes to the LWP tendency. A sensitivity study was then conducted, which investigated the effects of uncertainties in the initialisation of the model by applying variations to the initialisation parameters that effect the LWP tendency. DALES outperformed RACMO in predicting stratocumulus occurrence. The model results also showed to be robust to the applied variations, i.e. the stratocumulus did not rapidly dissolve. These variations can have a great effect on the LWP, however. A model like DALES has a spin up time in which the fields grow from having small turbulent motions to being fully turbulent. Therefore a method was developed to initialise DALES with fully turbulent motions. The method was then applied to the Cold Air Outbreak case of January 31 2010. The results showed that initialising DALES in this way is successful, and that large scale structures were present at initialisation.

DALES
stratocumulus
forecasts
LES
modelling

http://resolver.tudelft.nl/uuid:2ce21fdd-9e82-4605-8e33-16ebfc7e7655

Student theses

master thesis

(c) 2016 Heuff, F.M.G.