An investigation of the surface fluxes and other parameters in the regional climate model RCA1 during ice conditions

In this study data from the regional climate model RCA1 is compared to measured data to investigate how good the model is during ice conditions and mainly how well the turbulent surface fluxes are described by the model. Comparisons of the sensible heat flux and the momentum flux as well as mean par...

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Bibliographic Details
Main Author: Tisell, Camilla
Format: Bachelor Thesis
Language:English
Published: Uppsala universitet, Luft-, vatten- och landskapslära 2004
Subjects:
RCA
Online Access:http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303758
Description
Summary:In this study data from the regional climate model RCA1 is compared to measured data to investigate how good the model is during ice conditions and mainly how well the turbulent surface fluxes are described by the model. Comparisons of the sensible heat flux and the momentum flux as well as mean parameters are included. The measured data used are from the Bothnian Bay measured during the BASIS field experiment in February to March 1998. RCA1 (Rossby Centre regional Atmospheric model) is a regional climate model for Northern Europe based on HIRLAM and forced by ERA-40 data. Two different grid points of the RCA1 44 km grid have been chosen with geographical coordinates as close as possible to the two measuring sites. The first site is a small peninsula south of the town Umeå at the east coast of Sweden and the second one is the ship R/V Aranda anchored in the sea ice outside the Finnish west coast. The model presents generally too large negative (downward) sensible heat fluxes and too large momentum fluxes over ice. The largest difference between modelled and measured sensible heat fluxes are seen after warm front passages due to melting conditions. There are some uncertainties in the comparison of modelled fluxes and measured fluxes at Umeå due to a complex and varying ice cover around this measuring site. The vertical structure in the atmosphere has also been studied and modelled temperature, wind and humidity profiles were compared to radiosondes at the Umeå site. Two periods with on-ice flow and off-ice flow was analysed and one of the main differences was that for the on-ice situation an internal boundary layer was built up over the ice. Modelled profiles are generally smoother then measured profiles and inversions and other small-scale phenomena like low-level jets are almost never described correctly by the model but there are tendencies of the phenomena to occur. Sammanfattning av ”En undersökning i hur bra den regionala klimatmodellen RCA1 beskriver olika parametrar över is, i huvudsak de turbulenta ...