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The surface energy balance of a snow cover: comparing measurements to two different simulation models
KTH, Superseded Departments, Civil and Environmental Engineering.
KTH, Superseded Departments, Civil and Environmental Engineering.
2001 (English)In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 70, no 1-4, 81-96 p.Article in journal (Refereed) Published
Abstract [en]

We compared two one-dimensional simulation models for heat and water fluxes in the soil-snow-atmosphere system with respect to their mathematical formulations of the surface heat exchange and the snow pack evolution. They were chosen as examples of a simple one-layer snow model and a more detailed multiple-layer snow model (SNTHERM). The snow models were combined with the same one-dimensional model for the heat and water balance of the underlying soil (CoupModel). Data from an arable field in central Sweden (Marsta), covering two years (1997-1999) of soil temperature, snow depth and eddy-correlation measurements were successfully compared with the models. Conditions with a snow pack deeper or shallower than 10cm and bare soil resulted in similar discrepancies. The simulated net radiation and sensible heat flux were in good agreement with that measured during snow-covered periods, except for situations with snowmelt when the downward sensible heat flux was overestimated by 10-20 WM-2. The results showed that the uncertainties in parameter values were more important than the model formulation and that both models were useful in evaluating the limitations and uncertainties of the measurements.

Place, publisher, year, edition, pages
2001. Vol. 70, no 1-4, 81-96 p.
Keyword [en]
LAND, PARAMETERIZATION, TEMPERATURE, RADIATION, WATER, SOIL
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-13341DOI: 10.1007/s007040170007ISI: 000172271800007OAI: oai:DiVA.org:kth-13341DiVA: diva2:323991
Note
QC 20100614Available from: 2010-06-14 Created: 2010-06-14 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Land surface heat exchange over snow and frozen soil
Open this publication in new window or tab >>Land surface heat exchange over snow and frozen soil
2001 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The energy exchange in the soil-snow-vegetation-atmospheresystem was studied to improve the quantitative knowledge of thegoverning processes. The lack of such knowledge contributes tothe uncertainty in the applicability of many existing modelsindependent of the temporal or spatial scale. The theoreticalbackground and available methods for measurements and numericalsimulations were reviewed. Numerical simulation models andavailable data sets representing open land and boreal forestwere evaluated in both diurnal and seasonal time-scales.Surface heat fluxes, snow depth, soil temperatures andmeteorological conditions were measured at an agriculturalfield in central Sweden over two winters, 1997-1999. Twoone-dimensional simulation models of different complexity wereused to simulate the heat and water transfer in thesoil-snow-atmosphere system and compared with the measurements.Comparison of simulated and observed heat fluxes showed thatparameter values governing the upper boundary condition weremore important than the formulation of the internal mass andheat balance of the snow cover. The models were useful toevaluate the lack of energy balance closure in the observedsurface heat fluxes, which underlined the importance ofimproved accuracy in eddy correlation measurements of latentflow during winter conditions.

The representation of boreal forest in the land surfacescheme used within a weather forecast model was tested with athree-year data set from the NOPEX forest site in centralSweden. The formulation with separate energy balances forvegetation and the soil/snow beneath tree cover improvedsimulation of the seasonal and diurnal variations of latent andsensible heat flux compared with an older model version.Further improvements of simulated surface heat fluxes could beexpected if the variation of vegetation properties within andbetween years and a new formulation of the boundary conditionsfor heat flux into the soil is included.

Keywords: Surface energy balance, Snow, Boreal forest,SVAT models, Eddy-correlation Measurements, Latent heat flux,Sensible heat flux, Net radiation, Soil temperature,Aerodynamic roughness, Surface resistance

Place, publisher, year, edition, pages
Stockholm: KTH, 2001. iv, 14 p.
Series
Trita-AMI. LIC, 2068
Keyword
Surface energy balance, Snow, Boreal forest, SVAT models, Eddy-correlation Measurements, Latent heat flux, Sensible heat flux, Net radiation, Soil temperature, Aerodynamic roughness, Surface resistance
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-1231 (URN)91-7283-061-1 (ISBN)
Note
QC 20100614Available from: 2001-06-18 Created: 2001-06-18 Last updated: 2010-06-14Bibliographically approved
2. Boreal land surface water and heat balance: Modelling soil-snow-vegetation-atmosphere behaviour
Open this publication in new window or tab >>Boreal land surface water and heat balance: Modelling soil-snow-vegetation-atmosphere behaviour
2002 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The water and heat exchange in thesoil-snow-vegetation-atmosphere system was studied in order toimprove the quantitative knowledge of land surface processes.In this study, numerical simulation models and availabledatasets representing arable land, sub-alpine snowpack, andboreal forest were evaluated at both diurnal and seasonaltimescales.

Surface heat fluxes, snow depth, soil temperatures andmeteorological conditions were measured at an agriculturalfield in central Sweden during three winters and two summersfrom 1997 to 2000 within the WINTEX project. A one-dimensionalsimulation model (COUP) was used to simulate the water and heatbalance of the field. Comparison of simulated and measured heatfluxes in winter showed that parameter values governing theupper boundary condition were more important for explainingmeasured fluxes than the formulation of the internal mass andheat balance of the snow cover. The assumption of steady stateheat exchange between the surface and the reference height wasinadequate during stable atmospheric conditions. Independentestimates of the soil heat and water balance together with thecomparison of simulated and measured surface heat fluxes showedthat the eddy-correlation estimates of latent heat fluxes fromthe arable field were on average 40 % too low.

The ability of a multi-layered snowpack model (SNTHERM) tosimulate the layered nature of a sub-alpine snowpack wasevaluated based on a dataset from Switzerland. The modelsimulated the seasonal development of snow depth and densitywith high accuracy. However, the models ability to reproducethe strong observed snowpack layering was limited by theneglection of the effect of snow microstructure on snowsettling, and a poor representation of water redistributionwithin the snowpack.

The representation of boreal forest in the land surfacescheme used within a weather forecast (ECMWF) model was testedwith a three-year dataset from the NOPEX forest site in centralSweden. The new formulation with separate energy balances forvegetation and the soil/snow beneath the tree cover improvedthe simulation of seasonal and diurnal variations in latent andsensible heat flux. Further improvements of simulated latentheat fluxes were obtained when seasonal variation in vegetationproperties was introduced. Application of the COUP model withthe same dataset showed that simulation of evaporation fromintercepted snow contributed to a better agreement with themeasured sensible heat flux above forests, but also indicatedthat the measurements might have underestimated latent heatflux. The winter sensible heat flux above the forest wasfurther improved if an upper limit of the aerodynamicresistance of 500 s m-1 was applied for stable conditions.

A comparison of the water and heat balance of arable landand forest confirmed the general knowledge of the differencesbetween these two surface types. The forest contributed withconsiderably more sensible heat flux to the atmosphere than thearable land in spring and summer due to the lower albedo andrelatively less latent heat flux. Latent heat flux from theforest was higher in winter due to the evaporation ofintercepted snow and rain. The net radiation absorbed by theforest was 60 % higher than that absorbed by the arable land,due to the lower surface albedo in winter.

Key words:soil; snow; land surface heat exchange;forest; arable land; eddy-correlation.

Place, publisher, year, edition, pages
Stockholm: KTH, 2002. xii, 26 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1002
Keyword
soil, snow, land surface heat exchange, forest, arable land, eddy-correlation
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-3406 (URN)91-7283-360-2 (ISBN)
Public defence
2002-10-04, 00:00
Note
QC 20100614Available from: 2002-09-23 Created: 2002-09-23 Last updated: 2010-06-14Bibliographically approved

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