2026-09-21T18:28:18Zhttps://helda.helsinki.fi/server/oai/request

oai:helda.helsinki.fi:10138/6023922026-07-23T15:16:08Zcom_10138_18086com_10138_17738col_10138_18093

Zhang, Xinyi Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta University of Helsinki, Faculty of Science Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten 2025-10-09T06:48:23Z 2025-10-09T06:48:23Z 2025-10-09 2025-07-31 http://hdl.handle.net/10138/602392 URN:NBN:fi:hulib-202510094358 The objective of this study is to statistically evaluate the surface wind speed simulated over Alps by the ICON high-resolution climate model. SYNOP observation is the reference of the simulated data. The evaluation is focusing on the perspectives of wind speed and wind directions. The analysis shows the simulation of wind varies in terrains and seasons. Wind speed simulated on mountain peaks and valleys are differently simulated in the model: dynamics is the main driver for wind speed simulated on peaks, and for valley wind speed, the main driver is thermodynamics. Wind speed simulated on mountain peaks is underestimated but its inter-daily variability is well reproduced except the large underestimation of daily wind speed variation due to the smoothing effect of the limited grid resolution in resolving the real orography. Surface wind on peaks is well simulated in summer when the PBL (Planetary Boundary Layer) is thick, so that the SYNOP observation stations and the corresponding grid pixels are within the PBL more often. Wind speed and daily wind speed variation simulated in valleys are overestimated due to the stronger vertical mixing in the shallower valleys in model than reality. It is best simulated in summer and winter, when the surface temperature is constantly warm or cold. Model performance on wind direction simulation is very well, nearly unbiased on terrain average. Wind direction is better simulated in winter than summer for both peaks and valleys. However, due to the different driven mechanisms behind the wind simulation over different terrains, the reason for better model performance in wind direction simulation in winter is different for them. On peaks, wind direction is better simulated due to the stable wind directions in synoptic scale due to dominant Siberian high pressure system. While in valleys, wind direction is better simulated in winter due to the cold surface, resulting in a stratified atmosphere in the valley; turbulence and vertical mixing is suppressed in this condition. eng Helsingin yliopisto University of Helsinki Helsingfors universitet CC BY 4.0 Complex terrain Global high-resolution climate simulation ICON Surface wind Meteorologia Meteorology Meteorologi Ilmakehätieteiden maisteriohjelma Master's Programme in Atmospheric Sciences Magisterprogrammet i atmosfärsvetenskaper Assessment of High-Resolution Simulation in Reproducing Surface Wind over Alps pro gradu -tutkielma master's thesis pro gradu -avhandling open.access